WorldWideScience

Sample records for band structure superconductivity

  1. Relativistic Model for two-band Superconductivity

    OpenAIRE

    Ohsaku, Tadafumi

    2003-01-01

    To understand the superconductivity in MgB2, several two-band models of superconductivity were proposed. In this paper, by using the relativistic fermion model, we clearize the effect of the lower band in the superconductivity.

  2. Pushing the Gradient Limitations of Superconducting Photonic Band Gap Structure Cells

    Energy Technology Data Exchange (ETDEWEB)

    Simakov, Evgenya I. [Los Alamos National Laboratory; Haynes, William B. [Los Alamos National Laboratory; Kurennoy, Sergey S. [Los Alamos National Laboratory; Shchegolkov, Dmitry [Los Alamos National Laboratory; O' Hara, James F. [Los Alamos National Laboratory; Olivas, Eric R. [Los Alamos National Laboratory

    2012-06-07

    Superconducting photonic band gap resonators present us with unique means to place higher order mode couples in an accelerating cavity and efficiently extract HOMs. An SRF PBG resonator with round rods was successfully tested at LANL demonstrating operation at 15 MV/m. Gradient in the SRF PBG resonator was limited by magnetic quench. To increase the quench threshold in PBG resonators one must design the new geometry with lower surface magnetic fields and preserve the resonator's effectiveness for HOM suppression. The main objective of this research is to push the limits for the high-gradient operation of SRF PBG cavities. A NCRF PBG cavity technology is established. The proof-of-principle operation of SRF PBG cavities is demonstrated. SRF PBG resonators are effective for outcoupling HOMs. PBG technology can significantly reduce the size of SRF accelerators and increase brightness for future FELs.

  3. The electronic structure of Nb3Al/Nb3Sn, a new test case for flat/steep band model of superconductivity

    Institute of Scientific and Technical Information of China (English)

    Yanlong Ding; Shuiquan Deng; Yong Zhao

    2014-01-01

    In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly flat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the ‘‘Flat/steep’’ band model than to the van-Hove singularity scenario. The flat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.

  4. Chiral CP2 skyrmions in three-band superconductors and layered superconducting structures

    Science.gov (United States)

    Garaud, Julien; Carlstrom, Johan; Babaev, Egor; Speight, Martin

    2013-03-01

    Recently discovered iron-based superconductors and well as multilayer structures involving s+/- superconductors can exhibit a spontaneous breaking of the time reversal symmetry. This raises the question of experimental manifestations of this additional broken symmetry. We demonstrate that it can result in formation of experimentally detectable nontrivial flux-carrying excitations which are topologically different conventional vortices. This new kind of solitons can provide an experimental signature of the breaking of time reversal symmetry. Supported by NSF CAREER Award DMR-0955902, Knut and Alice Wallenberg Foundation through the Royal Swedish Academy of Sciences and Swedish Research Council. And Swedish National Infrastructure for Computing (SNIC) at National Supercomputer Center.

  5. Revisiting orbital-fluctuation-mediated superconductivity in LiFeAs: Nontrivial spin-orbit interaction effects on the band structure and superconducting gap function

    Science.gov (United States)

    Saito, Tetsuro; Yamakawa, Youichi; Onari, Seiichiro; Kontani, Hiroshi

    2015-10-01

    The precise gap structure in LiFeAs (Tc=18 K) given by ARPES studies offers significant information that helps us understand the pairing mechanism in iron-based superconductors. The most remarkable characteristic in the LiFeAs gap structure would be that "the largest gap emerges on the tiny hole-pockets around the Z point." This result has been naturally explained in terms of the orbital-fluctuation scenario [T. Saito et al., Phys. Rev. B 90, 035104 (2014)], 10.1103/PhysRevB.90.035104, whereas the opposite result is obtained by the spin-fluctuation scenario. In this paper, we study the gap structure in LiFeAs by taking the spin-orbit interaction (SOI) into account, motivated by the recent ARPES studies that revealed a significant SOI-induced modification of the Fermi surface topology. For this purpose, we construct two possible tight-binding models with finite SOI by referring the band structures given by different ARPES groups. In addition, we extend the gap equation for multiorbital systems with finite SOI, and calculate the gap functions by applying the orbital-spin fluctuation theory. On the basis of both SOI-induced band structures, the main characteristics of the gap structure in LiFeAs are naturally reproduced only in the presence of strong interorbital interactions between (dx z /y z-dx y) orbitals. Thus the experimental gap structure in LiFeAs is a strong evidence for the orbital-fluctuation pairing mechanism.

  6. Superconducting Dome in a Gate-Tuned Band Insulator

    NARCIS (Netherlands)

    Ye, J. T.; Zhang, Y. J.; Akashi, R.; Bahramy, M. S.; Arita, R.; Iwasa, Y.

    2012-01-01

    A dome-shaped superconducting region appears in the phase diagrams of many unconventional superconductors. In doped band insulators, however, reaching optimal superconductivity by the fine-tuning of carriers has seldom been seen. We report the observation of a superconducting dome in the temperature

  7. Superconducting gap structure of FeSe.

    Science.gov (United States)

    Jiao, Lin; Huang, Chien-Lung; Rößler, Sahana; Koz, Cevriye; Rößler, Ulrich K; Schwarz, Ulrich; Wirth, Steffen

    2017-03-07

    The microscopic mechanism governing the zero-resistance flow of current in some iron-based, high-temperature superconducting materials is not well understood up to now. A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure. Here we present a combined study of low-temperature specific heat and scanning tunnelling microscopy measurements on single crystalline FeSe. The results reveal the existence of at least two superconducting gaps which can be represented by a phenomenological two-band model. The analysis of the specific heat suggests significant anisotropy in the gap magnitude with deep gap minima. The tunneling spectra display an overall "U"-shaped gap close to the Fermi level away as well as on top of twin boundaries. These results are compatible with the anisotropic nodeless models describing superconductivity in FeSe.

  8. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

    Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

  9. Tunneling in superconducting structures

    Science.gov (United States)

    Shukrinov, Yu. M.

    2010-12-01

    Here we review our results on the breakpoint features in the coupled system of IJJ obtained in the framework of the capacitively coupled Josephson junction model with diffusion current. A correspondence between the features in the current voltage characteristics (CVC) and the character of the charge oscillations in superconducting layers is demonstrated. Investigation of the correlations of superconducting currents in neighboring Josephson junctions and the charge correlations in neighboring superconducting layers reproduces the features in the CVC and gives a powerful method for the analysis of the CVC of coupled Josephson junctions. A new method for determination of the dissipation parameter is suggested.

  10. Physics of electrons in solids: Volume 1 - Solid state physics, band structure, superconductivity and magnetism; Volume 2 - Solid state physics, exercises and problems with keys; Physique des electrons dans les solides: Tome 1, structure de bandes, supraconductivite et magnetisme. Physique des electrons dans les solides: Tome 2, recueil d'exercices et de problemes

    Energy Technology Data Exchange (ETDEWEB)

    Alloul, H. [Paris-11 Univ., 91 - Orsay (France). Lab. de Physique des Solides

    2007-07-01

    The diversity of the macroscopic properties of solids like magnetism or superconductivity stems from the quantum states of electrons. Today only the experimental approach reveals the spectacular effects of these properties but basic concepts of quantum mechanics and of statistical physics are necessary to give an account of the link between the microscopic scale and the macroscopic world. The simple approach involving independent electrons gives a description of the electronic structure as energy bands that explains the existence of metals, isolators and semi-conductors. Magnetism and superconductivity can be understood only by taking into account the existence of correlations between the electrons in the solids. The first tome presents the formalism of quantum mechanics applied to the system formed by nuclei and the electrons in solids. Different issues like electronic structures in solids, electron transport, the microscopic origin of superconductivity, the magnetism of isolators, the dynamics of spin and magnetic resonance are explained. The second volume can be divided into 2 parts, the first part giving the keys of the questions arisen in the first volume while the second part propose a series of problems (with keys). These problems illustrate the topics presented in the first volume and deal with issues like optical properties of solids, electron bands, Peierls transition, phonons in solids, isolator-metal transition, cyclotron resonance, superconductivity of NbSe{sub 2}, electronic properties of La{sub 2}CuO{sub 4}, or the magnetism of thin films. (A.C.)

  11. Superconducting Electronic Film Structures

    Science.gov (United States)

    1991-02-14

    cubic, yttria stabilized, zirconia (YSZ) single crystals with (100) orientation and ao = 0.512 to 0.516 nm. Films were magnetron-sputtered... Crown by Solid-State and Vapor-Phase Epitaxy," IEEE Trans. Uagn. 25(2), 2538 (1989). 6. J. H. Kang, R. T. Kampwirth, and K. E. Gray, "Superconductivity...summarized in Fig. 1, are too high for SrTiO3 or yttria- stabilized zirconia (YSZ) to be used in rf applications. MgO, LaAIO 3 , and LaGaO3 have a tan 6

  12. Analysis of Photonic Band Gaps in a Two-Dimensional Triangular Lattice with Superconducting Hollow Rods

    Science.gov (United States)

    Diaz-Valencia, B. F.; Calero, J. M.

    2017-02-01

    In this work, we use the plane wave expansion method to calculate photonic band structures in two-dimensional photonic crystals which consist of high-temperature superconducting hollow rods arranged in a triangular lattice. The variation of the photonic band structure with respect to both, the inner radius and the system temperature, is studied, taking into account temperatures below the critical temperature of the superconductor in the low frequencies regime and assuming E polarization of the incident light. Permittivity contrast and nontrivial geometry of the hollow rods lead to the appearance of new band gaps as compared with the case of solid cylinders. Such band gaps can be modulated by means of the inner radius and system temperature.

  13. Superconductivity

    CERN Document Server

    Thomas, D B

    1974-01-01

    A short general review is presented of the progress made in applied superconductivity as a result of work performed in connection with the high-energy physics program in Europe. The phenomenon of superconductivity and properties of superconductors of Types I and II are outlined. The main body of the paper deals with the development of niobium-titanium superconducting magnets and of radio-frequency superconducting cavities and accelerating structures. Examples of applications in and for high-energy physics experiments are given, including the large superconducting magnet for the Big European Bubble Chamber, prototype synchrotron magnets for the Super Proton Synchrotron, superconducting d.c. beam line magnets, and superconducting RF cavities for use in various laboratories. (0 refs).

  14. Superconductivity in an electron band just above the Fermi level: possible route to BCS-BEC superconductivity.

    Science.gov (United States)

    Okazaki, K; Ito, Y; Ota, Y; Kotani, Y; Shimojima, T; Kiss, T; Watanabe, S; Chen, C-T; Niitaka, S; Hanaguri, T; Takagi, H; Chainani, A; Shin, S

    2014-02-28

    Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe(0.6)Se(0.4)(Tc = 14.5 K ~ 1.2 meV) in an accessible range below and above the Fermi level(EF) using ultra-high resolution laser angle-resolved photoemission spectroscopy. We uncover an electron band lying just 0.7 meV (~8 K) above EF at the Γ-point, which shows a sharp superconducting coherence peak with gap formation below Tc. The estimated superconducting gap Δ and Fermi energy [Symbol: see text]F indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-coupling BCS-like superconductivity in the hole band. The study identifies the possible route to BCS-BEC superconductivity.

  15. Electronic Structure of New Superconducting Perovskite MgCNi3

    Institute of Scientific and Technical Information of China (English)

    Li CHEN; Hua LI; Liangmo MEI

    2004-01-01

    The electronic structures of new superconducting perovskite MgCNis and related compounds MgCNi2T (T=Co, Fe,and Cu) have been studied using MS-Xα method. In MgCNi3, the main peak of density of states is located below the Fermi level and dominated by Ni d. From the results of total energy calculations, it was found that the number of Ni valence electron decreases faster for the Fe-doped case than that for the Co-doped case. The valence state of Ni changes from +1.43 in MgCNi2Co to +3.02 in MgCNi2Fe. It was confirmed that Co and Fe dopants in MgCNi3 behave as a source of d-band holes and the suppression of superconductivity occurs faster for the Fe-doped case than that for the Co-doped case. In order to explain the fact that Co and Fe dopants in MgCNi3 behave as a source of d-band holes rather than magnetic scattering centers that quench superconductivity, we have also investigated the effects of electron (Cu) doping on the superconductivity and found that both electron (Cu) doping and hole (Co, Fe)doping quench superconductivity exist. Comparing with the hole (Co) doping, there was no much difference between Cu and Co doping. This suggests that Co and Fe doping do not actas magnetic impurity.

  16. Strongly correlated impurity band superconductivity in diamond: X-ray spectroscopic evidence

    Directory of Open Access Journals (Sweden)

    G. Baskaran

    2006-01-01

    Full Text Available In a recent X-ray absorption study in boron doped diamond, Nakamura et al. have seen a well isolated narrow boron impurity band in non-superconducting samples and an additional narrow band at the chemical potential in a superconducting sample. We interpret the beautiful spectra as evidence for upper Hubbard band of a Mott insulating impurity band and an additional metallic 'mid-gap band' of a conducting 'self-doped' Mott insulator. This supports the basic framework of a recent theory of the present author of strongly correlated impurity band superconductivity (impurity band resonating valence bond, IBRVB theory in a template of a wide-gap insulator, with no direct involvement of valence band states.

  17. Microstrip microwave band gap structures

    Indian Academy of Sciences (India)

    V Subramanian

    2008-04-01

    Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available finite element methodology for comparison.

  18. Raising gradient limitations in 2.1 GHz superconducting photonic band gap accelerator cavities

    Energy Technology Data Exchange (ETDEWEB)

    Simakov, Evgenya I., E-mail: smirnova@lanl.gov; Arsenyev, Sergey A.; Haynes, W. Brian; Shchegolkov, Dmitry Yu.; Suvorova, Natalya A.; Tajima, Tsuyoshi [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States); Boulware, Chase H.; Grimm, Terry L. [Niowave, Inc., 1012 North Walnut Street, Lansing, Michigan 48906 (United States)

    2014-06-16

    We report results from recent 2.1 GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1 GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4 K and below 2 K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.

  19. Definitive experimental evidence for two-band superconductivity in MgB2.

    Science.gov (United States)

    Tsuda, S; Yokoya, T; Takano, Y; Kito, H; Matsushita, A; Yin, F; Itoh, J; Harima, H; Shin, S

    2003-09-19

    The superconducting-gap of MgB2 has been studied by high-resolution angle-resolved photoemission spectroscopy. The results show that superconducting gaps with values of 5.5 and 2.2 meV open on the sigma band and the pi band, respectively, but both the gaps close at the bulk transition temperature, providing a definitive experimental evidence for the two-band superconductivity with strong interband pairing interaction in MgB2. The experiments validate the role of k-dependent electron-phonon coupling as the origin of multiple-gap superconductivity as well as the high transition temperature of MgB2.

  20. Subgap transport in silicene-based superconducting hybrid structures

    Science.gov (United States)

    Li, Hai

    2016-08-01

    We investigate the influences of exchange field and perpendicular electric field on the subgap transport in silicene-based ferromagnetic/superconducting (FS) and ferromagnetic/superconducting/ferromagnetic (FSF) junctions. Owing to the unique buckling structure of silicene, the Andreev reflection and subgap conductance can be effectively modulated by a perpendicular electric field. It is revealed that the subgap conductance in the FS junction can be distinctly enhanced by an exchange field. Remarkably, resorting to the tunable band gap of silicene, an exclusive crossed Andreev reflection (CAR) process in the FSF junction can be realized within a wide range of related parameters. Moreover, in the FSF junction the exclusive CAR and exclusive elastic cotunneling processes can be switched by reversing the magnetization direction in one of the ferromagnetic regions.

  1. Optimizing the configuration of a superconducting photonic band gap accelerator cavity to increase the maximum achievable gradients

    Science.gov (United States)

    Simakov, Evgenya I.; Kurennoy, Sergey S.; O'Hara, James F.; Olivas, Eric R.; Shchegolkov, Dmitry Yu.

    2014-02-01

    We present a design of a superconducting rf photonic band gap (SRF PBG) accelerator cell with specially shaped rods in order to reduce peak surface magnetic fields and improve the effectiveness of the PBG structure for suppression of higher order modes (HOMs). The ability of PBG structures to suppress long-range wakefields is especially beneficial for superconducting electron accelerators for high power free-electron lasers (FELs), which are designed to provide high current continuous duty electron beams. Using PBG structures to reduce the prominent beam-breakup phenomena due to HOMs will allow significantly increased beam-breakup thresholds. As a result, there will be possibilities for increasing the operation frequency of SRF accelerators and for the development of novel compact high-current accelerator modules for the FELs.

  2. Two-band superconductivity in MgB2.

    Science.gov (United States)

    Iavarone, M; Karapetrov, G; Koshelev, A E; Kwok, W K; Crabtree, G W; Hinks, D G; Kang, W N; Choi, Eun-Mi; Kim, Hyun Jung; Kim, Hyeong-Jin; Lee, S I

    2002-10-28

    The study of the anisotropic superconductor MgB2 using a combination of scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps at Delta(1)=2.3 meV and Delta(2)=7.1 meV at 4.2 K. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multiband system. Temperature evolution of the tunneling spectra follows the BCS scenario [Phys. Rev. Lett. 3, 552 (1959)

  3. Superconductivity between standard types: Multiband versus single-band materials

    Energy Technology Data Exchange (ETDEWEB)

    Vagov, A.; Shanenko, A. A.; Milošević, M. V.; Axt, V. M.; Vinokur, V. M.; Aguiar, J. Albino; Peeters, F. M.

    2016-05-06

    In the nearest vicinity of the critical temperature, types I and II of conventional single-band superconductors interchange at the Ginzburg-Landau parameter κ = 1/√2. At lower temperatures this point unfolds into a narrow but finite interval of κ’s, shaping an intertype (transitional) domain in the (κ,T ) plane. In the present work, based on the extended Ginzburg-Landau formalism, we show that the same picture of the two standard types with the transitional domain in between applies also to multiband superconductors. However, the intertype domain notably widens in the presence of multiple bands and can become extremely large when the system has a significant disparity between the band parameters. It is concluded that many multiband superconductors, such as recently discovered borides and iron-based materials, can belong to the intertype regime.

  4. Design for a superconducting niobium RFQ structure

    Energy Technology Data Exchange (ETDEWEB)

    Shepard, K.W.; Kennedy, W.L.; Sagalovsky, L.

    1992-01-01

    This paper reports a design for a niobium superconducting RFQ operating at 192 Mhz. The structure is of the rod and post type, novel in that each of four rods is supported by two posts oriented radially with respect to the beam axis. Although the geometry has four-fold rotation symmetry, the dipole-quadrupole mode splitting is large, giving good mechanical tolerances. The simplicity of the geometry enables designing for good mechanical stability while minimizing tooling cost for fabrication with niobium. Results of MAFIA numerical modeling, measurements on a copper model, and plans for a beam test are discussed.

  5. Design for a superconducting niobium RFQ structure

    Energy Technology Data Exchange (ETDEWEB)

    Shepard, K.W.; Kennedy, W.L.; Sagalovsky, L.

    1992-09-01

    This paper reports a design for a niobium superconducting RFQ operating at 192 Mhz. The structure is of the rod and post type, novel in that each of four rods is supported by two posts oriented radially with respect to the beam axis. Although the geometry has four-fold rotation symmetry, the dipole-quadrupole mode splitting is large, giving good mechanical tolerances. The simplicity of the geometry enables designing for good mechanical stability while minimizing tooling cost for fabrication with niobium. Results of MAFIA numerical modeling, measurements on a copper model, and plans for a beam test are discussed.

  6. Construction of a superconducting RFQ structure

    Energy Technology Data Exchange (ETDEWEB)

    Shepard, K.W.; Kennedy, W.L. [Argonne National Lab., IL (United States); Crandall, K.R. [AccSys Technology, Inc., Pleasanton, CA (United States)

    1993-07-01

    This paper reports the design and construction status of a niobium superconducting RFQ operating at 194 MHz. The structure is of the rod and post type, novel in that each of four rods is supported by two posts oriented radially with respect to the beam axis. Although the geometry has four-fold rotation symmetry, the dipole-quadrupole mode splitting is large, giving good mechanical tolerances. The simplicity of the geometry enables designing for good mechanical stability while minimizing tooling costs for fabrication with niobium. Design details of a prototype niobium resonator, results of measurements on room temperature models, and construction status are discussed.

  7. Surface superconductivity of dirty two-band superconductors: applications to MgB2.

    Science.gov (United States)

    Gorokhov, Denis A

    2005-02-25

    The minimal magnetic field H(c2) destroying superconductivity in the bulk of a superconductor is smaller than the magnetic field H(c3) needed to destroy surface superconductivity if the surface of a superconductor coincides with one of the crystallographic planes and is parallel to the external magnetic field. While for a dirty single-band superconductor the ratio of H(c3) to H(c2) is a universal temperature-independent constant 1.6946, for dirty two-band superconductors this is not the case. I show that in the latter case the interaction of the two bands leads to a novel scenario with the ratio H(c3)/H(c2) varying with temperature and taking values larger and smaller than 1.6946. The results are applied to MgB(2) and compared with recent experiments (A. Rydh, cond-mat/0307445).

  8. Electronic structure and superconductivity of MgB2

    Indian Academy of Sciences (India)

    D M Gaitonde; P Modak; R S Rao; B K Godwal

    2003-01-01

    Results of ab initio electronic structure calculations on the compound, MgB2, using the FPLAPW method employing GGA for the exchange–correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated, $D(E_F)$ and the experimental specific heat data. The $T_c$ is found to be 37 K. We use a parametrized description of the calculated band structure to obtain the = 0 K values of the London penetration depth and the superconducting coherence length. The penetration depth calculated by us is too small and the coherence length too large as compared to the experimentally determined values of these quantities. This indicates the limitations of a theory that relies only on electronic structure calculations in describing the superconducting state in this material and implies that impurity effects as well as mass renormalization effects need to be included.

  9. Multi-band Eilenberger Theory of Superconductivity: Systematic Low-Energy Projection

    Science.gov (United States)

    Nagai, Yuki; Nakamura, Hiroki

    2016-07-01

    We propose the general multi-band quasiclassical Eilenberger theory of superconductivity to describe quasiparticle excitations in inhomogeneous systems. With the use of low-energy projection matrix, the M-band quasiclassical Eilenberger equations are systematically obtained from N-band Gor'kov equations. Here M is the internal degrees of freedom in the bands crossing the Fermi energy and N is the degree of freedom in a model. Our framework naturally includes inter-band off-diagonal elements of Green's functions, which have usually been neglected in previous multi-band quasiclassical frameworks. The resultant multi-band Eilenberger and Andreev equations are similar to the single-band ones, except for multi-band effects. The multi-band effects can exhibit the non-locality and the anisotropy in the mapped systems. Our framework can be applied to an arbitrary Hamiltonian (e.g., a tight-binding Hamiltonian derived by the first-principle calculation). As examples, we use our framework in various kinds of systems, such as noncentrosymmetric superconductor CePt3Si, three-orbital model for Sr2RuO4, heavy fermion CeCoIn5/YbCoIn5 superlattice, a topological superconductor with the strong spin-orbit coupling CuxBi2Se3, and a surface system on a topological insulator.

  10. Superconductivity in the A15 structure

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, G.R.

    2015-07-15

    Highlights: • Review of A-15 structure superconductors. • Comparison of A-15 superconductors with other superconducting classes. • Characteristic physical properties of A-15 superconductors. - Abstract: The cubic A15 structure metals, with over 60 distinct member compounds, held the crown of highest T{sub c} superconductor starting in 1954 with the discovery of T{sub c} = 18 K in Nb{sub 3}Sn. T{sub c} increased over the next 20 years until the discovery in 1973 of T{sub c} = 22.3 K (optimized to ≈23 K a year later) in sputtered films of Nb{sub 3}Ge. Attempts were made to produce – via explosive compression – higher (theorized to be 31–35 K) transition temperatures in not-stable-at-ambient-conditions A15 Nb{sub 3}Si. However, the effort to continue the march to higher T{sub c}’s in A15 Nb{sub 3}Si only resulted in a defect-suppressed T{sub c} of 19 K by 1981. Focus in superconductivity research partially shifted with the advent of heavy Fermion superconductors (CeCu{sub 2}Si{sub 2}, UBe{sub 13}, and UPt{sub 3} discovered in 1979, 1983 and 1984 respectively) and further shifted away from A15’s with the discovery of the perovskite structure cuprate superconductors in 1986 with T{sub c} = 35 K. However, the A15 superconductors – and specifically doped Nb{sub 3}Sn – are still the material of choice today for most applications where high critical currents (e.g. magnets with dc persistent fields up to 21 T) are required. Thus, this article discusses superconductivity, and the important physical properties and theories for the understanding thereof, in the A15’s which held the record T{sub c} for the longest time (32 years) of any known class of superconductor since the discovery of T{sub c} = 4.2 K in Hg in 1911. The discovery in 2008 of T{sub c} = 38 K at 7 kbar in A15 Cs{sub 3}C{sub 60} (properly a member of the fullerene superconductor class), which is an insulator at 1 atm pressure and otherwise also atypical of the A15 class of superconductors

  11. Evidence for two-band superconductivity from break-junction tunneling on MgB2.

    Science.gov (United States)

    Schmidt, H; Zasadzinski, J F; Gray, K E; Hinks, D G

    2002-03-25

    Superconductor-insulator-superconductor tunnel junctions have been fabricated on MgB2 that display Josephson and quasiparticle currents. These junctions exhibit a gap magnitude, Delta approximately 2.5 meV, that is considerably smaller than the BCS value, but which clearly and reproducibly closes near the bulk T(c). In conjunction with fits of the conductance spectra, these results are interpreted as direct evidence of two-band superconductivity.

  12. Crystal structure of the superconducting phase of sulfur hydride

    Science.gov (United States)

    Einaga, Mari; Sakata, Masafumi; Ishikawa, Takahiro; Shimizu, Katsuya; Eremets, Mikhail I.; Drozdov, Alexander P.; Troyan, Ivan A.; Hirao, Naohisa; Ohishi, Yasuo

    2016-09-01

    A superconducting critical temperature above 200 K has recently been discovered in H2S (or D2S) under high hydrostatic pressure. These measurements were interpreted in terms of a decomposition of these materials into elemental sulfur and a hydrogen-rich hydride that is responsible for the superconductivity, although direct experimental evidence for this mechanism has so far been lacking. Here we report the crystal structure of the superconducting phase of hydrogen sulfide (and deuterium sulfide) in the normal and superconducting states obtained by means of synchrotron X-ray diffraction measurements, combined with electrical resistance measurements at both room and low temperatures. We find that the superconducting phase is mostly in good agreement with the theoretically predicted body-centred cubic (bcc) structure for H3S. The presence of elemental sulfur is also manifest in the X-ray diffraction patterns, thus proving the decomposition mechanism of H2S to H3S + S under pressure.

  13. Gradient limitations in room temperature and superconducting acceleration structures

    Energy Technology Data Exchange (ETDEWEB)

    Solyak, N.A.; /Fermilab

    2008-10-01

    Accelerating gradient is a key parameter of the accelerating structure in large linac facilities, like future Linear Collider. In room temperature accelerating structures the gradient is limited mostly by breakdown phenomena, caused by high surface electric fields or pulse surface heating. High power processing is a necessary procedure to clean surface and improve the gradient. In the best tested X-band structures the achieved gradient is exceed 100 MV/m in of {approx}200 ns pulses for breakdown rate of {approx} 10{sup -7}. Gradient limit depends on number of factors and no one theory which can explain all sets of experimental results and predict gradient in new accelerating structure. In paper we briefly overview the recent experimental results of breakdown studies, progress in understanding of gradient limitations and scaling laws. Although superconducting rf technology has been adopted throughout the world for ILC, it has frequently been difficult to reach the predicted performance in these structures due to a number of factors: multipactoring, field emission, Q-slope, thermal breakdown. In paper we are discussing all these phenomena and the ways to increase accelerating gradient in SC cavity, which are a part of worldwide R&D program.

  14. Electronic structure and superconductivity of FeSe-related superconductors.

    Science.gov (United States)

    Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J

    2015-05-13

    FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films.

  15. s- and d-wave superconductivity in a two-band model

    Science.gov (United States)

    Reyes, Daniel; Continentino, Mucio A.; Thomas, Christopher; Lacroix, Claudine

    2016-10-01

    Superconductivity in strongly correlated systems is a remarkable phenomenon that attracts a huge interest. The study of this problem is relevant for materials such as the high Tc oxides, pnictides and heavy fermions. In this work we study a realistic model that includes the relevant physics of superconductivity in the presence of strong Coulomb correlations. We consider a two-band model, since most of these correlated systems have electrons from at least two different atomic orbitals coexisting at their Fermi surface. The Coulomb repulsion is taken into account through a local repulsive interaction. Pairing is considered among quasi-particles in neighboring sites and we allow for different symmetries of the order parameter. In order to deal with the strong local correlations, we use the well known slave boson approach that has proved very successful for this problem. Here we are interested in obtaining the zero temperature properties of the model, specifically its phase diagram and the existence and nature of superconducting quantum critical points. We show that these can arise by increasing the mixing between the two bands. Since this can be controlled by external pressure or doping, our results have a direct relation with experiments. We show that the superconductor-to-normal transition can be either to a metal, a correlated metal or to an insulator. Also we compare the relative stability of s and d-wave paired states for different regions of parameter space and investigate the BCS-BEC crossover in the two-band lattice model as function of the strength of the pairing interaction.

  16. Odd triplet superconductivity in superconductor ferromagnet structures: a survey

    Energy Technology Data Exchange (ETDEWEB)

    Bergeret, F.S. [Universidad Autonoma de Madrid, Departamento de Fisica Teorica de la Materia Condensada C-V, Madrid (Spain); Volkov, A.F. [Ruhr-Universitaet Bochum, Theoretische Physik III, Bochum (Germany); Russian Academy of Sciences, Institute for Radioengineering and Electronics, Moscow (Russian Federation); Efetov, K.B. [Ruhr-Universitaet Bochum, Theoretische Physik III, Bochum (Germany); L.D. Landau Institute for Theoretical Physics RAS, Moscow (Russian Federation)

    2007-11-15

    We review the main features of odd triplet superconductivity in superconductor-ferromagnet (S/F) structures. We discuss the different types of superconducting condensate that can be experimentally observed and pay special attention to the triplet component induced in a ferromagnet which is in contact with a superconductor. The triplet component is an even function of the momentum and an odd function of the frequency and leads to novel phenomena. (orig.)

  17. Microwave dependence of subharmonic gap structure in superconducting junctions

    DEFF Research Database (Denmark)

    Sørensen, O. Hoffman; Kofoed, Bent; Pedersen, Niels Falsig

    1974-01-01

    with the superconducting energy gap itself. The location in voltage of all these structures is given by eV=(2Δ±nh ν) / m, where 2Δ is the superconducting energy gap, ν is the applied frequency, h is Planck's constant, e is the magnitude of the electronic charge, V is the dc voltage drop across the junction, and m and n...

  18. Superconductivity

    Science.gov (United States)

    1989-07-01

    SUPERCONDUCTIVITY HIGH-POWER APPLICATIONS Electric power generation/transmission Energy storage Acoustic projectors Weapon launchers Catapult Ship propulsion • • • Stabilized...temperature superconductive shields could be substantially enhanced by use of high-Tc materials. 27 28 NRAC SUPERCONDUCTIVITY SHIP PROPULSION APPLICATIONS...motor shown in the photograph. As a next step in the evolution of electric-drive ship propulsion technology, DTRC has proposed to scale up the design

  19. Varactor-tuned superconducting filter with constant absolute bandwidth at VHF-band

    Energy Technology Data Exchange (ETDEWEB)

    Li, Bo [Department of Physics, Tsinghua University, Beijing 100084 (China); Cao, Bisong, E-mail: bscao@tsinghua.edu.cn [Department of Physics, Tsinghua University, Beijing 100084 (China); Guo, Xubo; Zhang, Xiaoping [Department of Physics, Tsinghua University, Beijing 100084 (China); Chen, Yidong [Superconductor Technology Co., Ltd, Beijing 100085 (China); Wei, Bin; Jiang, Linan [Department of Physics, Tsinghua University, Beijing 100084 (China)

    2015-09-15

    Highlights: • A four-pole superconducting tunable filter at VHF-band with constant absolute bandwidth is proposed. • The novel resonator consists of a spiral-in-spiral-out (SISO) microstrip line with one end shorted to ground and the other loaded with a varactor diode. • Both combline and interdigital constructions for coupling are introduced, and tuned to meet the constant bandwidth requirements. • The measurements show bandwidth variation is less than 1.3% while tuning from 247.28 to 266.58 MHz, and a high Q{sub u} of 1600–5500 is archived. - Abstract: A four-pole superconducting tunable filter at VHF-band with constant absolute bandwidth is proposed. The resonator consists of a spiral-in-spiral-out (SISO) resonator with one end shorted to ground and the other end loaded with a varactor diode. Both combline and interdigital constructions for coupling are introduced, and tuned to meet the constant bandwidth requirement. The fabricated device has a compact size, a tuning range of 7.3% from 247.28 to 266.58, a 3-dB bandwidth of 2.32 ± 0.03 MHz. The insertion loss ranges from 0.5 to 1.6 dB, yielding a high unloaded Q of 1600–5500. The simulated and measured results show an excellent agreement.

  20. Effective band structure of random alloys.

    Science.gov (United States)

    Popescu, Voicu; Zunger, Alex

    2010-06-11

    Random substitutional A(x)B(1-x) alloys lack formal translational symmetry and thus cannot be described by the language of band-structure dispersion E(k(→)). Yet, many alloy experiments are interpreted phenomenologically precisely by constructs derived from wave vector k(→), e.g., effective masses or van Hove singularities. Here we use large supercells with randomly distributed A and B atoms, whereby many different local environments are allowed to coexist, and transform the eigenstates into an effective band structure (EBS) in the primitive cell using a spectral decomposition. The resulting EBS reveals the extent to which band characteristics are preserved or lost at different compositions, band indices, and k(→) points, showing in (In,Ga)N the rapid disintegration of the valence band Bloch character and in Ga(N,P) the appearance of a pinned impurity band.

  1. Strain and High Temperature Superconductivity: Unexpected Results from Direct Electronic Structure Measurements in Thin Films

    Science.gov (United States)

    Abrecht, M.; Ariosa, D.; Cloetta, D.; Mitrovic, S.; Onellion, M.; Xi, X.; Margaritondo, G.; Pavuna, D.

    2003-07-01

    Angle-resolved photoemission spectroscopy reveals very surprising strain-induced effects on the electronic band dispersion of epitaxial La2-xSrxCuO4-δ thin films. In strained films we measure a band that crosses the Fermi level (EF) well before the Brillouin zone boundary. This is in contrast to the flat band reported in unstrained single crystals and in our unstrained films, as well as in contrast to the band flattening predicted by band structure calculations for in-plane compressive strain. In spite of the density of states reduction near EF, the critical temperature increases in strained films with respect to unstrained samples. These results require a radical departure from commonly accepted notions about strain effects on high temperature superconductors, with possible general repercussions on superconductivity theory.

  2. Pressure dependence of structural phase transition and superconducting transition in CsI

    CERN Document Server

    Nirmala-Louis, C

    2003-01-01

    The self-consistent band structure calculation for CsI performed both in CsCl and HCP structures using the TB-LMTO method is reported. The equilibrium lattice constant, bulk modulus and the phase-transition pressure at which the compound undergoes structural phase transition from CsCl to HCP are predicted from the total-energy calculations. The band structure, density of states (DOS), electronic charge distributions, metallization and superconducting transition temperature (T sub c) of CsI are obtained as a function of pressure for both the CsCl and HCP structures. It is found that the charge transfer from s and p states to d state causes metallization and superconductivity in CsI. The highest T sub c estimated is 2.11 K and the corresponding pressure is 1.8 Mbar. This value is in agreement with the recent experimental observation. The experimental trend - ''metallization and superconductivity is rather insensitive to the crystal structure of CsI'' - is also confirmed in our work. (Abstract Copyright [2003], ...

  3. Structural analysis of superconducting dipole prototype for HIAF

    CERN Document Server

    Zhang, Xiaoying; Ni, Dongsheng; Chen, Yuquan; Wu, Wei; Ma, Lizhen

    2015-01-01

    The High Intensity Heavy-Ion Accelerator Facility is a new project in the Institute of Modern Physics. The dipole magnets of all rings are conceived as fast cycled superconducting magnet with high magnetic field and large gap, the warm iron and superconducting coil structure (superferric) is adopted. The reasonable structure design of coil and cryostat is very important for reliable operation. Based on the finite element software ANSYS, the mechanical analysis of electromagnetic stress, the thermal stress in the cooling down and the stress in the pumping are showed in detail. According to the analysis result, the supporter structure is the key problem of coil system. With reasonable support's structure design, the stress and the deformation of coil structure can be reduced effectively, which ensure the stable operation of superconducting coil system.

  4. Local Electronic Structure and High Temperature Superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Emery, V. J.; Kivelson, S. A.

    1999-02-08

    It is argued that a new mechanism and many-body theory of superconductivity are required for doped correlated insulators. Here they review the essential features of and the experimental support for such a theory, in which the physics is driven by the kinetic energy.

  5. One-Dimensional Anisotropic Band Gap Structure

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The band gap structure of one-dimensional anisotropic photonic crystal has been studied by means of the transfer matrix formalism. From the analytic expressions and numeric calculations we see some general characteristics of the band gap structure of anisotropic photonic crystals, each band separates into two branches and the two branches react to polarization sensitively. In the practical case of oblique incidence, gaps move towards high frequency when the angle of incidence increases. Under some special conditions, the two branches become degenerate again.

  6. Prediction of Superconductivity for Oxides Based on Structural Parameters and Artificial Neural Network Method

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Superconductive properties for oxides were predicted by artificial neural network (ANN) method with structural and chemical parameters as inputs. The predicted properties include superconductivity for oxides, distributed ranges of the superconductive transition temperature (Tc) for complex oxides, and Tc values for cuprate superconductors. The calculated results indicated that the adjusted ANN can be used to predict superconductive properties for unknown oxides.

  7. Complex band structure and superlattice electronic states

    Science.gov (United States)

    Schulman, J. N.; McGill, T. C.

    1981-04-01

    The complex band structures of the bulk materials which constitute the alternating layer (001) semiconductor-semiconductor superlattice are investigated. The complex bands near the center of the Brillouin zone in the [001] direction are studied in detail. The decay lengths of superlattice states whose energies lie in the bulk band gaps of one of the semiconductors are determined from the dispersion curves of these bands for imaginary k-->. This method is applied using a tight-binding band-structure calculation to two superlattices: the AlAs-GaAs superlattice and the CdTe-HgTe superlattice. The decay lengths of AlAs-GaAs superlattice conduction-band minimum states are found to be substantially shorter than those for the CdTe-HgTe superlattice. These differences in the decay of the states in the two superlattices result in differences in the variation of the conduction-band effective masses with the thickness of the AlAs and CdTe layers. The conduction-band effective masses increase more rapidly with AlAs thickness in the AlAs-GaAs superlattice than with CdTe thickness in the CdTe-HgTe superlattice.

  8. Quasiparticle Band Structure of BaS

    Institute of Scientific and Technical Information of China (English)

    LU Tie-Yu; CHEN De-Yan; HUANG Mei-Chun

    2006-01-01

    @@ We calculate the band structure of BaS using the local density approximation and the GW approximation (GWA),i.e. in combination of the Green function G and the screened Coulomb interaction W. The Ba 4d states are treated as valence states. We find that BaS is a direct band-gap semiconductor. The result shows that the GWA band gap (Eg-Gw = 3.921 eV) agrees excellently with the experimental result (Eg-EXPT = 3.88 eV or 3.9eV).

  9. Triplet superconductivity in oxide ferromagnetic interlayer of mesa-structure

    Science.gov (United States)

    Ovsyannikov, G. A.; Y Constantinian, K.; Sheerman, A. E.; Shadrin, A. V.; Kislinski, Yu V.; Khaydukov, Yu N.; Mustafa, L.; Kalabukhov, A.; Winkler, D.

    2015-03-01

    We present experimental data on Nb-Au/La0.7Sr0.3MnO3/SrRuO3/YBa2Cu3O7-δ mesa- structure with in plane linear size 10÷50 μm. The mesa-structures were patterned from the epitaxial heterostructures fabricated by pulsed laser ablation and magnetron sputtering. Superconducting critical current was observed for mesa-structures with the interlayer thicknesses up to 50 nm. In the mesa-structures with just one, either La0.7Sr0.3MnO3 or SrRuO3 interlayer with a thickness larger than 10 nm no superconducting current was observed. The registered superconducting current for the mesa-structures with a thinner interlayer is attributed to pinholes. Obtained results are discussed in terms of superconducting long-range triplet generation at interfaces of superconductor and a composite ferromagnet consisting of ferromagnetic materials with non-collinear magnetization.

  10. Superconductivity, the Structure Scale of the Universe

    CERN Document Server

    Saam, R D

    1997-01-01

    A lattice and associated superconducting theory is postulated whereby electromagnetic and gravitational forces are mediated by a particle of mass (110.39 x electron mass) such that the established electron/proton mass is maintained, electron and proton charge is maintained and the universe radius is 1.5E28 cm, the universe mass is 2.00E56 gram, the universe density is 1.45E-29 g/cm3, the universe time or age is 1.57E10 years and the universe Hubble constant is 2.47E-18/sec (76 km/sec-million parsec). The calculated universe mass and density are based on an isotropic homogeneous media filling the vacuum of space analogous to the 'ether' referred to in the 19th century and could be considered a candidate for the 'dark matter' in present universe theories. In this context the COBE satellite universe background microwave black body radiation temperature is linked to universe dark matter superconducting temperature. Also, a reasonable value for the cosmological constant is derived having dimensions of the known un...

  11. Possible Two-band Superconductivity In PuRhGa5 And CeRhIn5

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, E D [Los Alamos National Laboratory; Park, T [Los Alamos National Laboratory; Mcdonald, R D [Los Alamos National Laboratory; Graf, M J [Los Alamos National Laboratory; Boulaevskii, L N [Los Alamos National Laboratory; Mitchell, J N [Los Alamos National Laboratory; Thompson, J D [Los Alamos National Laboratory; Sarrao, J L [Los Alamos National Laboratory

    2008-01-01

    Measurements of the upper critical field H{sub c2} of the Pu-based heavy-fermion superconductor PuRhGa{sub 5} have been made using a torque magnetometer at temperatures down to 0.6 K and magnetic fields up to 17 T along the principal axes of the tetragonal structure. A linear temperature dependence of H{sub c2} down to T{sub c}/10 for H {parallel} c and to T{sub c}/2 for H {parallel} ab is observed. While the data appear to be inconsistent with both purely Pauli limiting or orbital effects governing the upper critical field, the linear T-dependence of H{sub c2} is well described by a two-band model of superconductivity involving coupled bands of heavy and light electrons. A close similarity between PuRhGa{sub 5} and the pressure-induced antiferromagnetic isostructural superconductor CeRhIn{sub 5} is also found.

  12. Line nodes and surface Majorana flat bands in static and kicked p -wave superconducting Harper model

    Science.gov (United States)

    Wang, Huai-Qiang; Chen, M. N.; Bomantara, Raditya Weda; Gong, Jiangbin; Xing, D. Y.

    2017-02-01

    We investigate the effect of introducing nearest-neighbor p -wave superconducting pairing to both the static and kicked extended Harper model with two periodic phase parameters acting as artificial dimensions to simulate three-dimensional systems. It is found that in both the static model and the kicked model, by varying the p -wave pairing order parameter, the system can switch between a fully gapped phase and a gapless phase with point nodes or line nodes. The topological property of both the static and kicked model is revealed by calculating corresponding topological invariants defined in the one-dimensional lattice dimension. Under open boundary conditions along the physical dimension, Majorana flat bands at energy zero (quasienergy zero and π ) emerge in the static (kicked) model at the two-dimensional surface Brillouin zone. For certain values of pairing order parameter, (Floquet) Su-Schrieffer-Heeger-like edge modes appear in the form of arcs connecting different (Floquet) Majorana flat bands. Finally, we find that in the kicked model, it is possible to generate two controllable Floquet Majorana modes, one at quasienergy zero and the other at quasienergy π , at the same parameter values.

  13. Maximizing band gaps in plate structures

    DEFF Research Database (Denmark)

    Halkjær, Søren; Sigmund, Ole; Jensen, Jakob Søndergaard

    2006-01-01

    Band gaps, i.e., frequency ranges in which waves cannot propagate, can be found in elastic structures for which there is a certain periodic modulation of the material properties or structure. In this paper, we maximize the band gap size for bending waves in a Mindlin plate. We analyze an infinite...... periodic plate using Bloch theory, which conveniently reduces the maximization problem to that of a single base cell. Secondly, we construct a finite periodic plate using a number of the optimized base cells in a postprocessed version. The dynamic properties of the finite plate are investigated...

  14. Band structure engineering in organic semiconductors

    Science.gov (United States)

    Schwarze, Martin; Tress, Wolfgang; Beyer, Beatrice; Gao, Feng; Scholz, Reinhard; Poelking, Carl; Ortstein, Katrin; Günther, Alrun A.; Kasemann, Daniel; Andrienko, Denis; Leo, Karl

    2016-06-01

    A key breakthrough in modern electronics was the introduction of band structure engineering, the design of almost arbitrary electronic potential structures by alloying different semiconductors to continuously tune the band gap and band-edge energies. Implementation of this approach in organic semiconductors has been hindered by strong localization of the electronic states in these materials. We show that the influence of so far largely ignored long-range Coulomb interactions provides a workaround. Photoelectron spectroscopy confirms that the ionization energies of crystalline organic semiconductors can be continuously tuned over a wide range by blending them with their halogenated derivatives. Correspondingly, the photovoltaic gap and open-circuit voltage of organic solar cells can be continuously tuned by the blending ratio of these donors.

  15. Structural materials for large superconducting magnets for tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Long, C.J.

    1976-12-01

    The selection of structural materials for large superconducting magnets for tokamak-type fusion reactors is considered. The important criteria are working stress, radiation resistance, electromagnetic interaction, and general feasibility. The most advantageous materials appear to be face-centered-cubic alloys in the Fe-Ni-Cr system, but high-modulus composites may be necessary where severe pulsed magnetic fields are present. Special-purpose structural materials are considered briefly.

  16. Production of S-band Accelerating Structures

    CERN Document Server

    Piel, C; Vogel, H; Vom Stein, P

    2004-01-01

    ACCEL currently produces accelerating structures for several scientific laboratories. Multi-cell cavities at S-band frequencies are required for the projects CLIC-driver-linac, DLS and ASP pre-injector linac and the MAMI-C microtron. Based on those projects differences and similarities in design, production technologies and requirements will be addressed.

  17. The crystal structure and superconducting properties of monatomic bromine.

    Science.gov (United States)

    Duan, Defang; Meng, Xing; Tian, Fubo; Chen, Changbo; Wang, Liancheng; Ma, Yanming; Cui, Tian; Liu, Bingbing; He, Zhi; Zou, Guangtian

    2010-01-13

    The crystal structure and superconducting properties of monatomic bromine under high pressure have been studied by first-principles calculations. We have found the following phase transition sequence with increasing pressure: from body-centered orthorhombic (bco, phase II) to body-centered tetragonal structure (bct, phase III) at 126 GPa, then to face-centered cubic structure (fcc, phase IV) at 157 GPa, which is stable at least up to 300 GPa. The calculated superconducting critical temperature T(c) = 1.46 K at 100 GPa is consistent with the experimental value of 1.5 K. In addition, our results of T(c) decrease with increasing pressure in all the monatomic phases of bromine, similar to monatomic iodine. Further calculations show that the decrease of λ with pressure in phase IV is mainly attributed to the weakening of the 'soft' vibrational mode caused by pressure.

  18. Vacuum impregnation with epoxy of large superconducting magnet structures

    Energy Technology Data Exchange (ETDEWEB)

    Green, M.A.; Coyle, D.E.; Miller, P.B.; Wenzel, W.F.

    1978-06-01

    The Lawrence Berkeley Laboratory (LBL) has been developing a new generation of superconducting magnets which have the helium cooling system as an integral part of the magnet structure. The LBL technique calls for large sections of the magnet structure to be vacuum impregnated with epoxy. The epoxy was chosen for its impregnation properties. Epoxies which have good impregnation characteristics are often subject to cracking when they are cooled to cryogenic temperatures. The cracking of such an epoxy can be controlled by: (1) minimizing the amount of epoxy in the structure; (2) reducing the size of unfilled epoxy spaces; and (3) keeping the epoxy in compression. The technique for using the epoxy is often more important than the formulation of the epoxy. The LBL vacuum impregnation and curing technique is described. Experimental measurements on small samples of coil sections are presented. Practical experience with large vacuum impregnation superconducting coils (up to two meters in dia) is also discussed.

  19. The role of engineered materials in superconducting tunnel junction X-ray detectors - Suppression of quasiparticle recombination losses via a phononic band gap

    Science.gov (United States)

    Rippert, Edward D.; Ketterson, John B.; Chen, Jun; Song, Shenian; Lomatch, Susanne; Maglic, Stevan R.; Thomas, Christopher; Cheida, M. A.; Ulmer, Melville P.

    1992-01-01

    An engineered structure is proposed that can alleviate quasi-particle recombination losses via the existence of a phononic band gap that overlaps the 2-Delta energy of phonons produced during recombination of quasi-particles. Attention is given to a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example. A device with a high density of Bragg resonances is identified as desirable; both Nb/Si and NbN/SiN superlattices have been produced, with the latter having generally superior performance.

  20. Quasiparticle band structure of antiferromagnetic Eu Te

    Energy Technology Data Exchange (ETDEWEB)

    Mathi Jaya, S.; Nolting, W. [Humboldt-Universitaet zu Berlin, Institut fuer Physik, Lehrstuhl Festkoerpertheorie, Invalidenstrasse 110, D-10115 Berlin (Germany)

    1997-11-24

    The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor Eu Te is derived by use of a combination of a many-body model procedure with a tight-binding-'linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d-f model for a single band electron ('test electron') being exchange coupled to the anti ferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d-f model are taken from a TB-LMTO calculation for paramagnetic Eu Te. The d-f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice-quasiparticle band structure (S-QBS) and sublattice-quasiparticle density of states (S-QDOS) of the unoccupied 5 d-6 s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles ('magnetic polarons') are worked out in detail. The temperature dependence of the S-QDOS and S-QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from T{sub N} to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5 d-6 s) conduction band electrons and localized 4 f moments. (author)

  1. Midfrequency band dynamics of large space structures

    Science.gov (United States)

    Coppolino, Robert N.; Adams, Douglas S.; Levine, Marie B.

    2004-09-01

    High and low intensity dynamic environments experienced by a spacecraft during launch and on-orbit operations, respectively, induce structural loads and motions, which are difficult to reliably predict. Structural dynamics in low- and mid-frequency bands are sensitive to component interface uncertainty and non-linearity as evidenced in laboratory testing and flight operations. Analytical tools for prediction of linear system response are not necessarily adequate for reliable prediction of mid-frequency band dynamics and analysis of measured laboratory and flight data. A new MATLAB toolbox, designed to address the key challenges of mid-frequency band dynamics, is introduced in this paper. Finite-element models of major subassemblies are defined following rational frequency-wavelength guidelines. For computational efficiency, these subassemblies are described as linear, component mode models. The complete structural system model is composed of component mode subassemblies and linear or non-linear joint descriptions. Computation and display of structural dynamic responses are accomplished employing well-established, stable numerical methods, modern signal processing procedures and descriptive graphical tools. Parametric sensitivity and Monte-Carlo based system identification tools are used to reconcile models with experimental data and investigate the effects of uncertainties. Models and dynamic responses are exported for employment in applications, such as detailed structural integrity and mechanical-optical-control performance analyses.

  2. Complex banded structures in directional solidification processes.

    Science.gov (United States)

    Korzhenevskii, A L; Rozas, R E; Horbach, J

    2016-01-27

    A combination of theory and numerical simulation is used to investigate impurity superstructures that form in rapid directional solidification (RDS) processes in the presence of a temperature gradient and a pulling velocity with an oscillatory component. Based on a capillary wave model, we show that the RDS processes are associated with a rich morphology of banded structures, including frequency locking and the transition to chaos.

  3. Banded electron structures in the plasmasphere

    Energy Technology Data Exchange (ETDEWEB)

    Burke, W.J.; Rubin, A.G.; Hardy, D.A.; Holeman, E.G.

    1995-05-01

    The low-energy plasma analyzer on CRRES has detected significant fluxes of 10-eV to 30-keV electrons trapped on plasmaspheric field lines. On energy versus time spectrograms these electrons appear as banded structures that can span the 2 < L < 6 range of magnetic shells. The authors present an example of banded electron structures, encountered in the nightside plasmasphere during the magnetically quiet January 30, 1991. Empirical analysis suggests that two clouds of low energy electrons were injected from the plasma sheet to L < 4 on January 26 and 27 while the convective electric field was elevated. The energies of electrons in the first cloud were greater than those in the second. DMSP F8 measurements show that after the second injection, the polar cap potential rapidly decreased from >50 to <20 kY. Subsequent encounters with the lower energy cloud on alternating CRRES orbits over the next 2 days showed a progressive, earthward movement of the electrons, inner boundary. Whistler and electron cyclotron harmonic emissions accompanied the most intense manifestations of cloud electrons. The simplest explanation of these measurements is that after initial injection, the AIfven boundary moved Outward, leaving the cloud electrons on closed drift paths. Subsequent fluctuations of the convective electric field penetrated the plasmasphere, transporting cloud elements inward. The magnetic shell distribution of electron temperatures in one of the banded structures suggests that radiative energy losses may be comparable in magnitude to gains due to adiabatic compression.

  4. Theories of subharmonic gap structures in superconducting junctions

    DEFF Research Database (Denmark)

    Hasselberg, L.E.; Levinsen, M. T.; Samuelsen, Mogens Rugholm

    1974-01-01

    The two theories of subharmonic gap structures in superconducting junctions, multiparticle tunneling and self-coupling due to an electromagnetic field set up by the ac Josephson current, are analyzed when microwaves are applied. Both theories give the same location in voltage for the microwave......-induced satellites and the same microwave-power dependence for the subharmonic gap structure and the satellites. Therefore other properties than these are to be considered in order to distinguish between the two theories. We suggest that self-coupling is the main cause of the subharmonic gap structure....

  5. The band-gap enhanced photovoltaic structure

    Science.gov (United States)

    Tessler, Nir

    2016-05-01

    We critically examine the recently suggested structure that was postulated to potentially add 50% to the photo-conversion efficiency of organic solar cells. We find that the structure could be realized using stepwise increase in the gap as long as the steps are not above 0.1 eV. We also show that the charge extraction is not compromised due to an interplay between the contact's space charge and the energy level modification, which result in a flat energy band at the extracting contact.

  6. Structure and superconductivity of isotope-enriched boron-doped diamond

    Directory of Open Access Journals (Sweden)

    Evgeny A Ekimov, Vladimir A Sidorov, Andrey V Zoteev, Yury B Lebed, Joe D Thompson and Sergey M Stishov

    2008-01-01

    Full Text Available Superconducting boron-doped diamond samples were synthesized with isotopes of 10B, 11B, 13C and 12C. We claim the presence of a carbon isotope effect on the superconducting transition temperature, which supports the 'diamond-carbon'-related nature of superconductivity and the importance of the electron–phonon interaction as the mechanism of superconductivity in diamond. Isotope substitution permits us to relate almost all bands in the Raman spectra of heavily boron-doped diamond to the vibrations of carbon atoms. The 500 cm−1 Raman band shifts with either carbon or boron isotope substitution and may be associated with vibrations of paired or clustered boron. The absence of a superconducting transition (down to 1.6 K in diamonds synthesized in the Co–C–B system at 1900 K correlates with the small boron concentration deduced from lattice parameters.

  7. Optimal RF Systems for Lightly Loaded Superconducting Structures

    CERN Document Server

    Zwart, Townsend; Graves, William S; Wang, D; Zolfaghari, Abbi

    2004-01-01

    Recent developments in the field of RF accelerators have created a demand for power amplifiers that can support very high accelerating gradients, 15-25 MV/m, in superconducting structures with extremely low losses. Free electron lasers (FEL’s) with modest beam current, I< 10 uA, or based on energy recovery linacs (ERL’s) may have intrinsic power demands of less than 1 kW/m. We present the design of an amplifier and external tuner system that will efficiently meet this requirement. The RF amplifier, an Inductive Output Tube (IOT), offers high AC/RF efficiency, flexible power output and switching capability without the need for external modulation. The tuner circuit makes use of low loss ferrite phase shifters to create a moderate quality standing wave (Q~100-1000) between the amplifier and the superconducting cavity. An alternative design based on a shorter cavity structure and employing solid state amplifiers is also presented. The expected performance characteristics of both systems are described.

  8. Band structure of superdeformed bands in odd-A Hg nuclei

    Institute of Scientific and Technical Information of China (English)

    陈星渠; 邢正

    1997-01-01

    Through particle-rotor model, band structure of superdeformed bands in odd-A Hg nuclei is analysed. An overall and excellent agreement between the calculated and observed kinematic and dynamic moments of inertia is obtained. The electromagnetic transition properties of SD bands can be used to identify the configuration with certainty.

  9. Structure of haloform intercalated C60 and its influence on superconductive properties.

    Science.gov (United States)

    Dinnebier, Robert E; Gunnarsson, Olle; Brumm, Holger; Koch, Erik; Stephens, Peter W; Huq, Ashfia; Jansen, Martin

    2002-04-05

    CHCl3 and CHBr3 intercalated C60 have attracted particular interest after a superconductivity transition temperature (Tc) of up to 117 K was discovered. We have determined the structure using synchrotron x-ray powder-diffraction and found that the expansion of the lattice mainly takes place in one dimension (triclinic b axis), leaving planes of C60 molecules on an approximately hexagonal, slightly expanded lattice. We have performed tight-binding band structure calculations for the surface layer. In spite of the slight expansion of the layers, for the range of dopings where a large Tc has been observed, the density of states at the Fermi energy is smaller for C60.2CHCl3 and C60.2CHBr3 than for C60. This suggests that the lattice expansion alone cannot explain the increase of Tc.

  10. Crystal structure, magnetic susceptibility and thermopower of superconducting and non-superconducting Nd1.85Ce0.15CuO4+#upsilone#

    DEFF Research Database (Denmark)

    Mangelschots, I.; Andersen, N.H.; Lebech, B.;

    1992-01-01

    patterns from samples prepared on-line at the spectrometer show that the structures of superconducting and non-superconducting samples are identical within the limits set by the statistical errors of our data. Simultaneous gas volumetric measurements reveal that DELTAyoxidized......An experimental study of superconducting and non-superconducting Nd1.85Ce0.15CuO4+y, including structure determination by neutron powder diffraction, recording of oxygen changes by gas volumetry, and susceptibility and thermoelectric measurements, is reported. Difference neutron diffraction...... from the superconducting to the non-superconducting state. Structural refinements confirm that Nd1.85Ce0.15CuO4+y has the T'-type tetragonal structure reported in the literature, but additional oxygen may be located on the apical O(3) oxygen site of the T-type structure, with a total oxygen content...

  11. Analysis and characterizations of planar transmission structures and components for superconducting and monolithic integrated circuits

    Science.gov (United States)

    Itoh, Tatsuo

    1992-01-01

    The research effort was continued to design and characterize superconducting transmission line structures. The research during this period was concentrated on the implementation of a superconductor into coplanar waveguide structures. First, the superconducting coplanar waveguide was examined, and compared with a superconducting microstrip line in terms of loss characteristics and their design aspects. Then, the research was carried on the design and characterization of the coplanar waveguide family in the packaging environment. The transition between the coaxial line to the conductor backed coplanar waveguide was also designed for the measurement of the superconducting conductor backed coplanar waveguide.

  12. A Theoretical Structure of High School Concert Band Performance

    Science.gov (United States)

    Bergee, Martin J.

    2015-01-01

    This study used exploratory (EFA) and confirmatory factor analysis (CFA) to verify a theoretical structure for high school concert band performance and to test that structure for viability, generality, and invariance. A total of 101 university students enrolled in two different bands rated two high school band performances (a "first"…

  13. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor.

    Science.gov (United States)

    Sahakyan, M; Tran, V H

    2016-05-25

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with [Formula: see text] K, [Formula: see text] and moderate electron-phonon coupling [Formula: see text]. Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump ([Formula: see text]) at T c, diminished superconducting energy gap ([Formula: see text]) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ([Formula: see text]), and a concave curvature of the [Formula: see text] line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter [Formula: see text]. The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, [Formula: see text] meV is observed and a sizeable ratio [Formula: see text] could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

  14. Fabrication of Silicon Backshorts with Improved Out-of-Band Rejection for Waveguide-Coupled Superconducting Detectors

    Science.gov (United States)

    Crowe, Erik J.; Bennett, Charles L.; Chuss, David T.; Denis, Kevin L.; Eimer, Joseph; Lourie, Nathan; Marriage, Tobias; Moseley, Samuel H.; Rostem, Karwan; Stevenson, Thomas R.; Towner, Deborah; U-yen, Kongpop; Wollack, Edward J.

    2012-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is a ground-based instrument that will measure the polarization of the cosmic microqave background to search for gravitational waves form a posited epoch of inflation early in the universe's history. This measurement will require integration of superconducting transition-edge sensors with microwave waveguide inputs with good conrol of systematic errors, such as unwanted coupling to stray signals at frequencies outside of a precisely defined microwave band. To address these needs we will present work on the fabrication of silicon quarter-wave backshorts for the CLASS 40GHz focal plane. The 40GHz backshort consists of three degeneratively doped silicon wafers. Two spacer wafers are micromachined with through wafer vins to provide a 2.0mm long square waveguide. The third wafer acts as the backshort cap. The three wafers are bonded at the wafer level by Au-Au thermal compression bonding then aligned and flip chip bonded to the CLASS detector at the chip level. The micromachining techniques used have been optimized to create high aspect ratio waveguides, silicon pillars, and relief trenches with the goal of providing improved out of band signal rejection. We will discuss the fabrication of integrated CLASS superconducting detectors with silicon quarter wave backshorts and present current measurement results.

  15. Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3.

    Science.gov (United States)

    Biscaras, J; Bergeal, N; Kushwaha, A; Wolf, T; Rastogi, A; Budhani, R C; Lesueur, J

    2010-10-05

    Transition metal oxides show a great variety of quantum electronic behaviours where correlations often have an important role. The achievement of high-quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial structures where new electronic orders take place. One of the most striking result in this area is the recent observation of a two-dimensional electron gas at the interface between a strongly correlated Mott insulator LaTiO(3) and a band insulator SrTiO(3). The mechanism responsible for such a behaviour is still under debate. In particular, the influence of the nature of the insulator has to be clarified. In this article, we show that despite the expected electronic correlations, LaTiO(3)/SrTiO(3) heterostructures undergo a superconducting transition at a critical temperature T(c)(onset)~300 mK. We have found that the superconducting electron gas is confined over a typical thickness of 12 nm and is located mostly on the SrTiO(3) substrate.

  16. Elucidating the stop bands of structurally colored systems through recursion

    CERN Document Server

    Amir, Ariel

    2012-01-01

    Interference phenomena are the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics; namely, specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer and solve it using recursion relations. We present experimental data for various beetles, whose optical structure resembles the proposed model. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursive relations. In order for these to converge, an infinitesimal amount of absorption needs to be present, reminiscent of the regularization procedures commonly used in physics calculations. Thus, using only the phenomenon of...

  17. Electronic structure of a superconducting topological insulator Sr-doped Bi{sub 2}Se{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Han, C. Q.; Chen, W. J.; Zhu, Fengfeng; Yao, Meng-Yu [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Li, H.; Li, Z. J.; Wang, M.; Gao, Bo F., E-mail: bo-f-gao@mail.sim.ac.cn [Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, Shanghai 200050 (China); Guan, D. D.; Liu, Canhua; Qian, Dong, E-mail: dqian@sjtu.edu.cn; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093 (China); Gao, C. L. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093 (China); Department of Physics, Fudan University, Shanghai 200433 (China)

    2015-10-26

    Using high-resolution angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy, the atomic and low energy electronic structure of the Sr-doped superconducting topological insulators (Sr{sub x}Bi{sub 2}Se{sub 3}) was studied. Scanning tunneling microscopy shows that most of the Sr atoms are not in the van der Waals gap. After Sr doping, the Fermi level was found to move further upwards when compared with the parent compound Bi{sub 2}Se{sub 3}, which is consistent with the low carrier density in this system. The topological surface state was clearly observed, and the position of the Dirac point was determined in all doped samples. The surface state is well separated from the bulk conduction bands in the momentum space. The persistence of separated topological surface state combined with small Fermi energy makes this superconducting material a very promising candidate for the time reversal invariant topological superconductor.

  18. Pauli Limiting and Multi-Band Superconductivity in KFe2As2 Studied by Small-Angle Neutron Scattering

    Science.gov (United States)

    Eskildsen, M. R.; Kuhn, S. J.; Kawano-Furukawa, H.; Ono, M.; Forgan, E. M.; Jellyman, E.; Riyat, R.; Lee, C. H.; Kihou, K.; Hardy, F.; Wolf, Th.; Meingast, C.; Gavilano, J. L.

    We have studied the intrinsic anisotropy of the superconducting state in KFe2As2, using used small-angle neutron scattering to image the vortex lattice (VL) as the applied magnetic field is rotated towards the FeAs planes. The anisotropy is found to be strongly field dependent, indicating multi-band superconductivity. Furthermore, the high field anisotropy significantly exceeds that of the upper critical field, providing further support for Pauli limiting in KFe2As2 for field applied along the basal plane. Finally, we are able determine the contribution to the field modulation in the mixed state due to Pauli Paramagnetic Effects by measuring both the non-spin flip and spin flip VL scattered intensity. This represents the first instance where all the effects listed above have been obtained simultaneously and in a comprehensive manner by a single experimental technique. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.

  19. Bi-directional evolutionary optimization for photonic band gap structures

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Fei [Centre for Innovative Structures and Materials, School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne, VIC 3001 (Australia); School of Civil Engineering, Central South University, Changsha 410075 (China); Huang, Xiaodong, E-mail: huang.xiaodong@rmit.edu.au [Centre for Innovative Structures and Materials, School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne, VIC 3001 (Australia); Key Laboratory of Advanced Technology for Vehicle Body Design & Manufacture, Hunan University, Changsha, 410082 (China); Jia, Baohua [Centre for Micro-Photonics, Faculty of Engineering & Industrial Science, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122 (Australia)

    2015-12-01

    Toward an efficient and easy-implement optimization for photonic band gap structures, this paper extends the bi-directional evolutionary structural optimization (BESO) method for maximizing photonic band gaps. Photonic crystals are assumed to be periodically composed of two dielectric materials with the different permittivity. Based on the finite element analysis and sensitivity analysis, BESO starts from a simple initial design without any band gap and gradually re-distributes dielectric materials within the unit cell so that the resulting photonic crystal possesses a maximum band gap between two specified adjacent bands. Numerical examples demonstrated the proposed optimization algorithm can successfully obtain the band gaps from the first to the tenth band for both transverse magnetic and electric polarizations. Some optimized photonic crystals exhibit novel patterns markedly different from traditional designs of photonic crystals.

  20. The complex band structure for armchair graphene nanoribbons

    Institute of Scientific and Technical Information of China (English)

    Zhang Liu-Jun; Xia Tong-Sheng

    2010-01-01

    Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N= 3M-1. The band gap is almost unchanged for N = 3M + 1, but decreased for N = 3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nmaoribbons, and is also classified into three classes.

  1. Introduction to Superconducting RF Structures and the Effect of High Pressure Rinsing

    Energy Technology Data Exchange (ETDEWEB)

    Tajima, Tsuyoshi [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-06-30

    This presentation begins by describing RF superconductivity and SRF accelerating structures. Then the use of superconducting RF structures in a number of accelerators around the world is reviewed; for example, the International Linear Collider (ILC) will use ~16,000 SRF cavities with ~2,000 cryomodules to get 500 GeV e⁺/e⁻ colliding energy. Field emission control was (and still is) a very important practical issue for SRF cavity development. It has been found that high-pressure ultrapure water rinsing as a final cleaning step after chemical surface treatment resulted in consistent performance of single- and multicell superconducting cavities.

  2. Superconducting properties in tantalum decorated three-dimensional graphene and carbon structures

    Energy Technology Data Exchange (ETDEWEB)

    Cobaleda, Cayetano S. F., E-mail: ccobaleda@usal.es, E-mail: wpan@sandia.gov [Sandia National Laboratories, P.O. Box 5800, MS 1086, Albuquerque, New Mexico 87185 (United States); Laboratorio de Bajas Temperaturas, Universidad de Salamanca, E-37008 Salamanca (Spain); Xiao, Xiaoyin; Burckel, D. Bruce; Polsky, Ronen; Pan, W., E-mail: ccobaleda@usal.es, E-mail: wpan@sandia.gov [Sandia National Laboratories, P.O. Box 5800, MS 1086, Albuquerque, New Mexico 87185 (United States); Huang, Duanni [Sandia National Laboratories, P.O. Box 5800, MS 1086, Albuquerque, New Mexico 87185 (United States); Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States); Diez, Enrique [Laboratorio de Bajas Temperaturas, Universidad de Salamanca, E-37008 Salamanca (Spain)

    2014-08-04

    We present here the results on superconducting properties in tantalum thin films (100 nm thick) deposited on three-dimensional graphene (3DG) and carbon structures. A superconducting transition is observed in both composite thin films with a superconducting transition temperature of 1.2 K and 1.0 K, respectively. We have further measured the magnetoresistance at various temperatures and differential resistance dV/dI at different magnetic fields in these two composite thin films. In both samples, a much large critical magnetic field (∼2 T) is observed and this critical magnetic field shows linear temperature dependence. Finally, an anomalously large cooling effect was observed in the differential resistance measurements in our 3DG-tantalum device when the sample turns superconducting. Our results may have important implications in flexible superconducting electronic device applications.

  3. Pressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride.

    Science.gov (United States)

    Pan, Xing-Chen; Chen, Xuliang; Liu, Huimei; Feng, Yanqing; Wei, Zhongxia; Zhou, Yonghui; Chi, Zhenhua; Pi, Li; Yen, Fei; Song, Fengqi; Wan, Xiangang; Yang, Zhaorong; Wang, Baigeng; Wang, Guanghou; Zhang, Yuheng

    2015-07-23

    Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 T. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we boost the electronic properties by applying a high pressure, and introduce superconductivity successfully. Superconductivity sharply appears at a pressure of 2.5 GPa, rapidly reaching a maximum critical temperature (Tc) of 7 K at around 16.8 GPa, followed by a monotonic decrease in Tc with increasing pressure, thereby exhibiting the typical dome-shaped superconducting phase. From theoretical calculations, we interpret the low-pressure region of the superconducting dome to an enrichment of the density of states at the Fermi level and attribute the high-pressure decrease in Tc to possible structural instability. Thus, tungsten ditelluride may provide a new platform for our understanding of superconductivity phenomena in transition metal dichalcogenides.

  4. Band structures in the nematic elastomers phononic crystals

    Science.gov (United States)

    Yang, Shuai; Liu, Ying; Liang, Tianshu

    2017-02-01

    As one kind of new intelligent materials, nematic elastomers (NEs) represent an exciting physical system that combines the local orientational symmetry breaking and the entropic rubber elasticity, producing a number of unique physical phenomena. In this paper, the potential application of NEs in the band tuning is explored. The band structures in two kinds of NE phononic crystals (PCs) are investigated. Through changing NE intrinsic parameters, the influence of the porosity, director rotation and relaxation on the band structures in NE PCs are analyzed. This work is a meaningful try for application of NEs in acoustic field and proposes a new intelligent strategy in band turning.

  5. Cryogenic deformation of high temperature superconductive composite structures

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, Peter R. (Groton, MA); Michels, William (Brookline, MA); Bingert, John F. (Jemez Springs, NM)

    2001-01-01

    An improvement in a process of preparing a composite high temperature oxide superconductive wire is provided and involves conducting at least one cross-sectional reduction step in the processing preparation of the wire at sub-ambient temperatures.

  6. Broadening of effective photonic band gaps in biological chiral structures: From intrinsic narrow band gaps to broad band reflection spectra

    Science.gov (United States)

    Vargas, W. E.; Hernández-Jiménez, M.; Libby, E.; Azofeifa, D. E.; Solis, Á.; Barboza-Aguilar, C.

    2015-09-01

    Under normal illumination with non-polarized light, reflection spectra of the cuticle of golden-like and red Chrysina aurigans scarabs show a structured broad band of left-handed circularly polarized light. The polarization of the reflected light is attributed to a Bouligand-type left-handed chiral structure found through the scarab's cuticle. By considering these twisted structures as one-dimensional photonic crystals, a novel approach is developed from the dispersion relation of circularly polarized electromagnetic waves traveling through chiral media, to show how the broad band characterizing these spectra arises from an intrinsic narrow photonic band gap whose spectral position moves through visible and near-infrared wavelengths.

  7. Band structures in Sierpinski triangle fractal porous phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Kai; Liu, Ying, E-mail: yliu5@bjtu.edu.cn; Liang, Tianshu

    2016-10-01

    In this paper, the band structures in Sierpinski triangle fractal porous phononic crystals (FPPCs) are studied with the aim to clarify the effect of fractal hierarchy on the band structures. Firstly, one kind of FPPCs based on Sierpinski triangle routine is proposed. Then the influence of the porosity on the elastic wave dispersion in Sierpinski triangle FPPCs is investigated. The sensitivity of the band structures to the fractal hierarchy is discussed in detail. The results show that the increase of the hierarchy increases the sensitivity of ABG (Absolute band gap) central frequency to the porosity. But further increase of the fractal hierarchy weakens this sensitivity. On the same hierarchy, wider ABGs could be opened in Sierpinski equilateral triangle FPPC; whilst, a lower ABG could be opened at lower porosity in Sierpinski right-angled isosceles FPPCs. These results will provide a meaningful guidance in tuning band structures in porous phononic crystals by fractal design.

  8. Atomic structure of amorphous shear bands in boron carbide.

    Science.gov (United States)

    Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

    2013-01-01

    Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

  9. Band structure approach to the resonant x-ray scattering

    OpenAIRE

    Elfimov, I. S.; Skorikov, N. A.; Anisimov, V. I.; Sawatzky, G.A.

    2001-01-01

    We study the resonance behaviour of the forbidden 600 and 222 x-ray Bragg peaks in Ge using LDA band structure methods. These Bragg peaks remain forbidden in the resonant dipole scattering approximation even taking into account the non local nature of the band states. However they become allowed at resonance if the eigenstates of the unoccupied conduction band involve a hybridization of p like and d like atomic states. We show that the energy dependence of the resonant behaviour, including th...

  10. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon.

    Science.gov (United States)

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-05-27

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing.

  11. Electronic structure of heavy fermions: narrow temperature-independent bands

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Joyce, J.J.; Andrews, A.B.; Thompson, J.D.; Smith, J.L. [Los Alamos National Lab., NM (United States); Moshopoulou, E.; Fisk, Z. [NHMFL, Florida State Univ., Tallahassee, FL (United States); Menovsky, A.A. [Amsterdam Univ. (Netherlands). Natuurkundig Lab.; Canfield, P.C.; Olson, C.G. [Iowa State Univ., Ames, IA (United States). Ames Lab.

    1997-02-01

    The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from ARPES data reported here for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable. (orig.).

  12. The electronic structure of heavy fermions: Narrow temperature independent bands

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B. [and others

    1996-08-01

    The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.

  13. Inter-band phase fluctuations in macroscopic quantum tunneling of multi-gap superconducting Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Asai, Hidehiro, E-mail: hd-asai@aist.go.jp [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ota, Yukihiro [CCSE, Japan Atomic Energy Agency, Kashiwa, Chiba 277-8587 (Japan); Kawabata, Shiro [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Nori, Franco [CEMS, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, MI 48109-1040 (United States)

    2014-09-15

    Highlights: • We study MQT in Josephson junctions composed of multi-gap superconductors. • We derive a formula of the MQT escape rate for multiple phase differences. • We investigate the effect of inter-band phase fluctuation on MQT. • The MQT escape rate is significantly enhanced by the inter-band phase fluctuation. - Abstract: We theoretically investigate macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multi-gap superconductor. In such Josephson junctions, phase differences for each tunneling channel are defined, and the fluctuation of the relative phase differences appear which is referred to as Josephson–Leggett’s mode. We take into account the effect of the fluctuation in the tunneling process and calculate the MQT escape rate for various junction parameters. We show that the fluctuation of relative phase differences drastically enhances the escape rate.

  14. STRUCTURE AND SUPERCONDUCTIVITY OF Mg(B1-xCx)2 COMPOUNDS

    Institute of Scientific and Technical Information of China (English)

    ZHANG SHAO-YING; CHENG ZHAO-HUA; SHEN BAO-GEN; RONG CHUAN-BING; ZHAO TONG-YUN; ZHANG JIAN

    2001-01-01

    In this paper, we report on the structural properties and superconductivity of Mg(B1-xCx)2 compounds. Powder X-ray diffraction results indicate that the samples crystallize in a hexagonal AlB2-type structure. Due to the chemical activity of Mg powders, a small amount of MgO impurity phase is detected by X-ray diffraction. The lattice parameters decrease slightly with the increasing carbon content. Magnetization measurements indicate that the non-stoichiometry of MgB2 has no influence on the superconducting transition temperature and the transition temperature width. The addition of carbon results in a decrease of Tc and an increase of the superconducting transition width, implying the loss of superconductivity.

  15. Structure of nearly degenerate dipole bands in {sup 108}Ag

    Energy Technology Data Exchange (ETDEWEB)

    Sethi, J. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Palit, R., E-mail: palit@tifr.res.in [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Saha, S.; Trivedi, T. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Bhat, G.H.; Sheikh, J.A. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Datta, P. [Ananda Mohan College, Kolkata 700009 (India); Carroll, J.J. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Chattopadhyay, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Donthi, R. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Garg, U. [University of Notre Dame, Notre Dame, IN 46556 (United States); Jadhav, S.; Jain, H.C. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Karamian, S. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Kumar, S. [University of Delhi, Delhi 110007 (India); Litz, M.S. [US Army Research Laboratory, Adelphi, MD 20783 (United States); Mehta, D. [Panjab University, Chandigarh 160014 (India); Naidu, B.S. [Tata Institute of Fundamental Research, Colaba, Mumbai 400 005 (India); Naik, Z. [Sambalpur University, Sambalpur 143005 (India); Sihotra, S. [Panjab University, Chandigarh 160014 (India); and others

    2013-08-09

    The high spin negative parity states of {sup 108}Ag have been investigated with the {sup 11}B + {sup 100}Mo reaction at 39 MeV beam energy using the INGA facility at TIFR, Mumbai. From the γ–γ coincidence analysis, an excited negative parity band has been established and found to be nearly degenerate with the ground state band. The spin and parity of the levels are assigned using angular correlation and polarization measurements. This pair of degenerate bands in {sup 108}Ag is studied using the recently developed microscopic triaxial projected shell model approach. The observed energy levels and the ratio of the electromagnetic transition probabilities of these bands in this isotope are well reproduced by the present model. Further, it is shown that the partner band has a different quasiparticle structure as compared to the yrast band.

  16. Unfolding the band structure of non-crystalline photonic band gap materials.

    Science.gov (United States)

    Tsitrin, Samuel; Williamson, Eric Paul; Amoah, Timothy; Nahal, Geev; Chan, Ho Leung; Florescu, Marian; Man, Weining

    2015-08-20

    Non-crystalline photonic band gap (PBG) materials have received increasing attention, and sizeable PBGs have been reported in quasi-crystalline structures and, more recently, in disordered structures. Band structure calculations for periodic structures produce accurate dispersion relations, which determine group velocities, dispersion, density of states and iso-frequency surfaces, and are used to predict a wide-range of optical phenomena including light propagation, excited-state decay rates, temporal broadening or compression of ultrashort pulses and complex refraction phenomena. However, band calculations for non-periodic structures employ large super-cells of hundreds to thousands building blocks, and provide little useful information other than the PBG central frequency and width. Using stereolithography, we construct cm-scale disordered PBG materials and perform microwave transmission measurements, as well as finite-difference time-domain (FDTD) simulations. The photonic dispersion relations are reconstructed from the measured and simulated phase data. Our results demonstrate the existence of sizeable PBGs in these disordered structures and provide detailed information of the effective band diagrams, dispersion relation, iso-frequency contours, and their angular dependence. Slow light phenomena are also observed in these structures near gap frequencies. This study introduces a powerful tool to investigate photonic properties of non-crystalline structures and provides important effective dispersion information, otherwise difficult to obtain.

  17. Electronic structure of NiO: Correlation and band effects

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Z. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); List, R.S. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Dessau, D.S.; Wells, B.O. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); Jepsen, O. (Max-Planck-Institute for Solid State Research, D-7000 Stuttgart 80 (Federal Republic of Germany)); Arko, A.J.; Barttlet, R. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Shih, C.K. (Department of Physics, University of Texas, Austin, Texas (USA)); Parmigiani, F. (IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California (USA)); Huang, J.C.; Lindberg, P.A.P. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA))

    1991-08-15

    We have performed angle-resolved-photoemission experiments and local-density-functional (LDA) band calculations on NiO to study correlation and band effects of this conceptually important compound. Our experimental result suggests a dual nature of the electronic structure of NiO. On the one hand, the LDA band calculation has some relevance to the electronic structure of NiO, and the inclusion of the antiferromagnetic order is essential. For the lower O 2{ital p} bands, the LDA calculation agrees almost perfectly with experimental energy positions and dispersion relations. On the other hand, discrepancies between the experiment and the LDA calculation do exist, especially for the Ni 3{ital d} bands and the O 2{ital p} bands that are heavily mixed with the Ni 3{ital d} bands. It appears that the main discrepancies between the experimental results and the LDA calculation are concentrated in the regions of the insulating gap and the valence-band satellite. In addition to these results, we also report the interesting angle and photon-energy dependence of the satellite emission. The above results show that the angle-resolved-photoemission studies can provide much additional information about the electronic structure of correlated materials like NiO.

  18. Band Structure in Yang-Mills Theories

    CERN Document Server

    Bachas, Constantin

    2016-01-01

    We show how Yang-Mills theory on $S^3\\times R$ can exhibit a spectrum with continuous bands if coupled either to a topological 3-form gauge field, or to a dynamical axion with heavy Peccei-Quinn scale. The basic mechanism consists in associating winding histories to a bosonic zero mode whose role is to convert a circle in configuration space into a helix. The zero mode is, respectively, the holonomy of the 3-form field or the axion momentum. In these models different theta sectors coexist but are not mixed by local operators. Our analysis sheds light on, and extends Seiberg's proposal for modifying the topological sums in quantum field theories. It refutes a recent claim that $B+L$ violation at LHC is unsuppressed.

  19. Physical properties and electronic band structure of noncentrosymmetric Th7Co3 superconductor

    Science.gov (United States)

    Sahakyan, M.; Tran, V. H.

    2016-05-01

    The physical properties of the noncentrosymmetric superconductor Th7Co3 have been investigated by means of ac-magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance and Hall effect measurements. From these data it is established that Th7Co3 is a dirty type-II superconductor with {{T}\\text{c}}=1.8+/- 0.02 K, Hc2\\text{orb}text{kOe}c2p and moderate electron-phonon coupling {λ\\text{el-\\text{ph}}}=0.56 . Some evidences for anisotropic superconducting gap are found, including e.g. reduced specific heat jump (Δ {{C}p}/γ {{T}\\text{c}}=1.01 ) at T c, diminished superconducting energy gap ({{Δ }0}/{{k}\\text{B}}{{T}\\text{c}}=2.17 ) as compared to the BCS values, power law field dependence of the Sommerfeld coefficient at 0.4 K ({{C}p}/T\\propto {{H}0.6} ), and a concave curvature of the {{H}c2}≤ft({{T}\\text{c}}\\right) line. The magnitudes of the thermodynamic critical field and the energy gap are consistent with mean-squared anisotropy parameter ˜ 0.23 . The electronic specific heat in the superconducting state is reasonably fitted to an oblate spheroidal gap model. Calculations of scalar relativistic and fully relativistic electronic band structures reveal considerable differences in the degenerate structure, resulting from asymmetric spin-orbit coupling (ASOC). A large splitting energy of spin-up spin-down bands at the Fermi level E F, Δ {{E}\\text{ASOC}}˜ 100 meV is observed and a sizeable ratio Δ {{E}\\text{ASOC}}/{{k}\\text{B}}{{T}\\text{c}}˜ 640 could classify the studied compound into the class of noncentrosymmetric superconductors with strong ASOC. The noncentrosymmetry of the crystal structure and the atomic relativistic effects are both responsible for an importance of ASOC in Th7Co3. The calculated results for the density of states show a Van Hove singularity just below E F and dominant role of the 6d electrons of Th to the superconductivity.

  20. Unfolding the band structure of GaAsBi

    Science.gov (United States)

    Maspero, R.; Sweeney, S. J.; Florescu, Marian

    2017-02-01

    Typical supercell approaches used to investigate the electronic properties of GaAs(1-x)Bi(x) produce highly accurate, but folded, band structures. Using a highly optimized algorithm, we unfold the band structure to an approximate E≤ft(\\mathbf{k}\\right) relation associated with an effective Brillouin zone. The dispersion relations we generate correlate strongly with experimental results, confirming that a regime of band gap energy greater than the spin-orbit-splitting energy is reached at around 10% bismuth fraction. We also demonstrate the effectiveness of the unfolding algorithm throughout the Brillouin zone (BZ), which is key to enabling transition rate calculations, such as Auger recombination rates. Finally, we show the effect of disorder on the effective masses and identify approximate values for the effective mass of the conduction band and valence bands for bismuth concentrations from 0-12%.

  1. Band structure characteristics of T-square fractal phononic crystals

    Institute of Scientific and Technical Information of China (English)

    Liu Xiao-Jian; Fan You-Hua

    2013-01-01

    The T-square fractal two-dimensional phononic crystal model is presented in this article.A comprehensive study is performed for the Bragg scattering and locally resonant fractal phononic crystal.We find that the band structures of the fractal and non-fractal phononic crystals at the same filling ratio are quite different through using the finite element method.The fractal design has an important impact on the band structures of the two-dimensional phononic crystals.

  2. Band Gap Properties of Magnetoelectroelastic Grid Structures with Initial Stress

    Institute of Scientific and Technical Information of China (English)

    WANG Yi-Ze; LI Feng-Ming

    2012-01-01

    The propagation of elastic waves in magnetoelectroelastic grid structures is studied.Band gap properties are presented and the effects of the magnetoelectroelastic coupling and initial stress are considered. Numerical calculations are performed using the plane-wave expansion method.The results show that the band gap width can be tuned by the initial stress.It is hoped that our results will be helpful for designing acoustic filters with magnetoelectroelastic materials and grid structures.

  3. Optimum design of band-gap beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    -sectional area. To study the band-gap for travelling waves, a repeated inner segment of the optimized beams is analyzed using Floquet theory and the waveguide finite element (WFE) method. Finally, the frequency response is computed for the optimized beams when these are subjected to an external time......The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded...

  4. Nonequilibrium band structure of nano-devices

    Science.gov (United States)

    Hackenbuchner, S.; Sabathil, M.; Majewski, J. A.; Zandler, G.; Vogl, P.; Beham, E.; Zrenner, A.; Lugli, P.

    2002-03-01

    A method is developed for calculating, in a consistent manner, the realistic electronic structure of three-dimensional (3-D) heterostructure quantum devices under bias and its current density close to equilibrium. The nonequilibrium electronic structure is characterized by local Fermi levels that are calculated self-consistently. We have applied this scheme to predict asymmetric Stark shifts and tunneling of confined electrons and holes in single-dot GaAs/InGaAs photodiodes.

  5. Automated effective band structures for defective and mismatched supercells

    Science.gov (United States)

    Brommer, Peter; Quigley, David

    2014-12-01

    In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus k band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures.

  6. Electronic structure of the valence band of II--VI wide band gap semiconductor interfaces

    OpenAIRE

    1996-01-01

    In this work we present the electronic band structure for (001)--CdTe interfaces with some other II--VI zinc blende semiconductors. We assume ideal interfaces. We use tight binding Hamiltonians with an orthogonal basis ($s p^3 s^*$). We make use of the well--known Surface Green's Function Matching method to calculate the interface band structure. In our calculation the dominion of the interface is constituted by four atomic layers. We consider here anion--anion interfaces only. We have includ...

  7. Band-structure engineering in conjugated 2D polymers.

    Science.gov (United States)

    Gutzler, Rico

    2016-10-26

    Conjugated polymers find widespread application in (opto)electronic devices, sensing, and as catalysts. Their common one-dimensional structure can be extended into the second dimension to create conjugated planar sheets of covalently linked molecules. Extending π-conjugation into the second dimension unlocks a new class of semiconductive polymers which as a consequence of their unique electronic properties can find usability in numerous applications. In this article the theoretical band structures of a set of conjugated 2D polymers are compared and information on the important characteristics band gap and valence/conduction band dispersion is extracted. The great variance in these characteristics within the investigated set suggests 2D polymers as exciting materials in which band-structure engineering can be used to tailor sheet-like organic materials with desired electronic properties.

  8. Hubbard-U band-structure methods

    DEFF Research Database (Denmark)

    Albers, R.C.; Christensen, Niels Egede; Svane, Axel

    2009-01-01

    -body techniques such as using dynamical mean-field theory. We review the physics underlying these approaches and discuss their strengths and weaknesses in terms of the larger issues of electronic structure that they involve. In particular, we argue that the common assumptions made to justify such calculations...

  9. Structural properties of superconducting Bi-2223/Ag tapes

    Energy Technology Data Exchange (ETDEWEB)

    Gottschalck Andersen, L.

    2001-05-01

    The structural properties of silver clad high-T{sub c} superconducting ceramic tapes of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) have been investigated by means of synchrotron X-ray diffraction (including the 3DXRD microscope setup), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDS). By synchrotron X-ray diffraction in situ studies of the phase development during the transformation of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub x} (Bi-2212) into Bi-2223, the stoichiometry changes and the texture have been performed during annealing in 8% O{sub 2} and in air. Furthermore, an annealing with two high temperature cycles has been performed to study the equilibrium phenomena. During heating (Ca,Sr){sub 2}PbO{sub 4} decomposes at temperatures between 700 deg. C and 840 deg.C. Simultaneously, the Bi-2212 lattice contracts, indicating an incorporation of Pb. Moreover, the grain mis-alignment decreases significantly. In air we have observed that Bi-2212 partly dissociates into (Ca,Sr){sub 2}CuO{sub 3} and a liquid at temperatures above 812 deg. C. At the annealing temperature Bi-2212 and (Ca,Sr){sub 2}CuO{sub 3} react with the liquid to form Bi-2223. The transformation mechanism is discussed. During cooling below {approx}750 deg.C (Ca,Sr){sub 2}CuO{sub 3} and the liquid mainly transform into Bi-2201. Below {approx}780 deg. C Bi-2223 decomposes to 3221. In addition, a two-step cooling experiment and a decomposition study have been performed in 8% O{sub 2}. By TEM the grain and colony size in the c-axis direction, the angles of c-axis tilt grain boundaries and the intergrowth content are investigated. A fully processed tape has on average 50% thicker grains than a tape after the 1st annealing. The angles of c-axis tilt grain boundaries are on average 14 deg. and 26 deg. for the fully processed tape and the tape after the 1st annealing, respectively. The intergrowth content (15%) and

  10. Millimeter-wave waveguiding using photonic band structures

    Science.gov (United States)

    Eliyahu, Danny; Sadovnik, Lev S.; Manasson, Vladimir A.

    2000-07-01

    Current trends in device miniaturization and integration, especially in the development of microwave monolithic integrated circuits, calls for flexible, arbitrarily shaped and curved interconnects. Standard dielectric waveguides and microstrip lines are subject to prohibitive losses and their functionality is limited because of their unflexible structures. The problem is addressed by confining the wave- guiding path in a substrate with a Photonic Band Gap structure in a manner that will result in the guided mode being localized within the band gap. Two devices implementing Photonic Band Structures for millimeter waves confinement are presented. The first waveguide is a linear defect in triangular lattice created in a silicon slab (TE mode). The structure consists of parallel air holes of circular cross sections. The silicon was laser drilled to create the 2D crystal. The second device consists of alumina rods arranged in a triangular lattice, surrounded by air and sandwiched between two parallel metal plates (TM mode). Electromagnetic wave (W-band) confinement was obtained in both devices for straight and bent waveguides. Three branch waveguides (intersecting line defects) was studied as well. Measurements confirmed the lowloss waveguide confinement property of the utilizing Photonic Band Gap structure. This structure can find applications in power combiner/splitter and other millimeter wave devices.

  11. Band Structure in the Doubly Magic Nucleus 56Ni

    Institute of Scientific and Technical Information of China (English)

    DONG Bao-Guo; GUO Hong-Chao

    2004-01-01

    @@ Band structures near yrast lines of the Z = N doubly magic nucleus 56Ni are investigated with the configurationdependent cranked Nilsson-Strutinsky approach. The observed deformed bands are confirmed as highly deformed and their properties are explained theoretically. The calculated transition quadrupole moments Qt, ~ 1.7 eb at low spin as well as the kinematic and dynamic moments of inertia J1) and J(2) for configurations of interest are found to be generally in good agreement with the observed results. Two terminating states at 20+ and 29- for the two observed bands and other terminations in 56Ni are also predicted. It is found that the configuration-dependent cranked Nilsson-Strutinsky approach is better in the description of nuclear properties and band structures at high spin than other models.

  12. Coupling between Fano and Bragg bands in photonic band structure of two-dimensional metallic photonic structures

    CERN Document Server

    Markos, Peter

    2016-01-01

    Frequency and transmission spectrum of two-dimensional array of metallic rods is investigated numerically. Based on the recent analysis of the band structure of two-dimensional photonic crystal with dielectric rods [P. Marko\\v{s}, Phys. Rev. A 92 043814 (2015)] we identify two types of bands in the frequency spectrum: Bragg (P) bands resulting from a periodicity and Fano (F) bands which arise from Fano resonances associated with each of the cylinders within the periodic structure. It is shown that the existence of Fano band in a certain frequency range is manifested by a Fano resonance in the transmittance. In particular, we re-examine the symmetry properties of the H- polarized band structure in the frequency range where the spectrum consists of the localized modes associated with the single scatterer resonances and we explore process of formation of Fano bands by identifying individual terms in the expansion of the LCAO states. We demonstrate how the interplay between the two scattering mechanisms affects p...

  13. Band structures and localization properties of aperiodic layered phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yan Zhizhong, E-mail: zzyan@bit.edu.cn [Department of Applied Mathematics, Beijing Institute of Technology, Beijing 100081 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57078 Siegen (Germany)

    2012-03-15

    The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

  14. Band structures and localization properties of aperiodic layered phononic crystals

    Science.gov (United States)

    Yan, Zhi-Zhong; Zhang, Chuanzeng

    2012-03-01

    The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

  15. Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

    Science.gov (United States)

    Yastrubchak, O.; Wosinski, T.; Gluba, L.; Andrearczyk, T.; Domagala, J. Z.; Żuk, J.; Sadowski, J.

    2014-01-01

    The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

  16. Superconducting accelerating structures for very low velocity ion beams

    Energy Technology Data Exchange (ETDEWEB)

    Xu, J.; Shepard, K.W.; Ostroumov, P.N.; Fuerst, J.D.; Waldschmidt, G.; /Argonne; Gonin, I.V.; /Fermilab

    2008-01-01

    This paper presents designs for four types of very-low-velocity superconducting accelerating cavity capable of providing several MV of accelerating potential per cavity, and suitable for particle velocities in the range 0.006 < v/c < 0.06. Superconducting TEM-class cavities have been widely applied to CW acceleration of ion beams. SC linacs can be formed as an array of independently-phased cavities, enabling a variable velocity profile to maximize the output energy for each of a number of different ion species. Several laboratories in the US and Europe are planning exotic beam facilities based on SC linacs. The cavity designs presented here are intended for the front-end of such linacs, particularly for the post-acceleration of rare isotopes of low charge state. Several types of SC cavities have been developed recently to cover particle velocities above 0.06c. Superconducting four-gap quarter-wave resonators for velocities 0.008 < {beta} = v/c < 0.05 were developed about two decades ago and have been successfully operated at the ATLAS SC linac at Argonne National Laboratory. Since that time, progress in simulation tools, cavity fabrication and processing have increased SC cavity gradients by a factor of 3-4. This paper applies these tools to optimize the design of a four-gap quarter-wave resonator for exotic beam facilities and other low-velocity applications.

  17. Structure and superconductivity of double-doped Mg1-x(Al0.5Li0.5)xB2

    DEFF Research Database (Denmark)

    Xu, G.J.; Grivel, Jean-Claude; Abrahamsen, A.B.;

    2003-01-01

    A series of polycrystalline samples of Mg1-x(Al0.5Li0.5)(x)B-2 (0less than or equal toxless than or equal to0.6) were prepared by a solid state reaction method and their structure, superconducting transition temperature and magneto-transport properties were investigated by means of X-ray diffract......A series of polycrystalline samples of Mg1-x(Al0.5Li0.5)(x)B-2 (0less than or equal toxless than or equal to0.6) were prepared by a solid state reaction method and their structure, superconducting transition temperature and magneto-transport properties were investigated by means of X......-ray diffraction (XRD), ac-susceptibility and resistance in varied magnetic fields. The double doping leads to decreases in both the lattice parameters a and c. The superconducting transition temperature (T-c) decreases with double doping, but the T-c is systematically higher than that of the single Al......-doped samples. It is suggested that the hole band filling has little effect on T-c at high doping level, while the disorder induced by doping plays an important role in suppressing T-c. A systematic comparison with Al-doped MgB2 of the structure, superconducting transition and irreversibility field is made. (C...

  18. Complex band structure of topological insulator Bi2Se3

    Science.gov (United States)

    Betancourt, J.; Li, S.; Dang, X.; Burton, J. D.; Tsymbal, E. Y.; Velev, J. P.

    2016-10-01

    Topological insulators are very interesting from a fundamental point of view, and their unique properties may be useful for electronic and spintronic device applications. From the point of view of applications it is important to understand the decay behavior of carriers injected in the band gap of the topological insulator, which is determined by its complex band structure (CBS). Using first-principles calculations, we investigate the dispersion and symmetry of the complex bands of Bi2Se3 family of three-dimensional topological insulators. We compare the CBS of a band insulator and a topological insulator and follow the CBS evolution in both when the spin-orbit interaction is turned on. We find significant differences in the CBS linked to the topological band structure. In particular, our results demonstrate that the evanescent states in Bi2Se3 are non-trivially complex, i.e. contain both the real and imaginary contributions. This explains quantitatively the oscillatory behavior of the band gap obtained from Bi2Se3 (0 0 0 1) slab calculations.

  19. Bulk band structure of Bi2Te3

    DEFF Research Database (Denmark)

    Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco;

    2014-01-01

    -electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where...... distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators....

  20. Microtraps for neutral atoms using superconducting structures in the critical state

    CERN Document Server

    Emmert, Andreas; Brune, Michel; Raimond, Jean-Michel; Haroche, Serge; Nogues, Gilles

    2009-01-01

    Recently demonstrated superconducting atom-chips provide a platform for trapping atoms and coupling them to solid-state quantum systems. Controlling these devices requires a full understanding of the supercurrent distribution in the trapping structures. For type-II superconductors, this distribution is hysteretic in the critical state due to the partial penetration of the magnetic field in the thin superconducting film through pinned vortices. We report here an experimental observation of this memory effect. Our results are in good agreement with the redictions of the Bean model of the critical state without adjustable parameters. The memory effect allows to write and store permanent currents in micron-sized superconducting structures and paves the way towards new types of engineered trapping potentials.

  1. Microtraps for neutral atoms using superconducting structures in the critical state

    Science.gov (United States)

    Emmert, A.; Lupaşcu, A.; Brune, M.; Raimond, J.-M.; Haroche, S.; Nogues, G.

    2009-12-01

    Recently demonstrated superconducting atom chips provide a platform for trapping atoms and coupling them to solid-state quantum systems. Controlling these devices requires a full understanding of the supercurrent distribution in the trapping structures. For type-II superconductors, this distribution is hysteretic in the critical state due to the partial penetration of the magnetic field in the thin superconducting film through pinned vortices. We report here an experimental observation of this memory effect. Our results are in good agreement with the predictions of the Bean model of the critical state without adjustable parameters. The memory effect allows to write and store permanent currents in micron-sized superconducting structures and paves the way toward engineered trapping potentials.

  2. Tunable band structure and effective mass of disordered chalcopyrite

    Science.gov (United States)

    Wang, Ze-Lian; Xie, Wen-Hui; Zhao, Yong-Hong

    2017-02-01

    The band structure and effective mass of disordered chalcopyrite photovoltaic materials Cu1- x Ag x Ga X 2 ( X = S, Se) are investigated by density functional theory. Special quasirandom structures are used to mimic local atomic disorders at Cu/Ag sites. A local density plus correction method is adopted to obtain correct semiconductor band gaps for all compounds. The bandgap anomaly can be seen for both sulfides and selenides, where the gap values of Ag compounds are larger than those of Cu compounds. Band gaps can be modulated from 1.63 to 1.78 eV for Cu1- x Ag x Ga Se 2, and from 2.33 to 2.64 eV for Cu1- x Ag x Ga S 2. The band gap minima and maxima occur at around x = 0:5 and x = 1, respectively, for both sulfides and selenides. In order to show the transport properties of Cu1- x Ag x Ga X 2, the effective mass is shown as a function of disordered Ag concentration. Finally, detailed band structures are shown to clarify the phonon momentum needed by the fundamental indirect-gap transitions. These results should be helpful in designing high-efficiency photovoltaic devices, with both better absorption and high mobility, by Ag-doping in CuGa X 2.

  3. Superconductivity in Y6Tr4Al43 (Tr = Nb, Mo, Ta) with Peanut-Shaped Cage Structure

    Science.gov (United States)

    Kase, Naoki; Satoh, Ryoh; Nakano, Tomohito; Takeda, Naoya

    2016-10-01

    Superconductivity is discovered in Y6Tr4Al43 (Tr = Nb, Mo, Ta) with a peanut-shaped cage structure at Tc = 0.86, 0.75, and 0.68 K, respectively. The superconducting state is revealed by performing electrical resistivity and specific heat measurements. The upper critical field is obtained to be 0.22 (Nb), 0.175 (Mo), and 0.15 T (Ta). A specific heat jump provides evidence of bulk superconductivity in these compounds.

  4. Band structure analysis in SiGe nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Amato, Michele [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy); Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy); Palummo, Maurizia [European Theoretical Spectroscopy Facility (ETSF) (Italy); CNR-INFM-SMC, Dipartimento di Fisica, Universita di Roma, ' Tor Vergata' , via della Ricerca Scientifica 1, 00133 Roma (Italy); Ossicini, Stefano, E-mail: stefano.ossicini@unimore.it [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy) and Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy) and European Theoretical Spectroscopy Facility - ETSF (Italy) and Centro Interdipartimentale ' En and Tech' , Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy)

    2012-06-05

    One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.

  5. Comparison of structural transformations and superconductivity in compressed sulfur and selenium

    Energy Technology Data Exchange (ETDEWEB)

    Rudin, Sven P.; Liu, Amy Y.; Freericks, J. K.; Quandt, Alexander

    2001-06-01

    Density-functional calculations are presented for high-pressure structural phases of S and Se. The structural phase diagrams, phonon spectra, electron-phonon coupling, and superconducting properties of the isovalent elements are compared. We find that with increasing pressure, Se adopts a sequence of ever more closely packed structures ({beta}-Po, bcc, fcc), while S favors more open structures ({beta}-Po, simple cubic, bcc). These differences are shown to be attributable to differences in the S and Se core states. All the compressed phases of S and Se considered are calculated to have weak to moderate electron-phonon coupling strengths consistent with superconducting transition temperatures in the range of 1 to 20 K. Our results compare well with experimental data on the {beta}-Po{r_arrow}bcc transition pressure in Se and on the superconducting transition temperature in {beta}-PoS. Further experiments are suggested to search for the other structural phases predicted at higher pressures and to test theoretical results on the electron-phonon interaction and superconducting properties.

  6. Superconductivity in doped Dirac semimetals

    Science.gov (United States)

    Hashimoto, Tatsuki; Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2016-07-01

    We theoretically study intrinsic superconductivity in doped Dirac semimetals. Dirac semimetals host bulk Dirac points, which are formed by doubly degenerate bands, so the Hamiltonian is described by a 4 ×4 matrix and six types of k -independent pair potentials are allowed by the Fermi-Dirac statistics. We show that the unique spin-orbit coupling leads to characteristic superconducting gap structures and d vectors on the Fermi surface and the electron-electron interaction between intra and interorbitals gives a novel phase diagram of superconductivity. It is found that when the interorbital attraction is dominant, an unconventional superconducting state with point nodes appears. To verify the experimental signature of possible superconducting states, we calculate the temperature dependence of bulk physical properties such as electronic specific heat and spin susceptibility and surface state. In the unconventional superconducting phase, either dispersive or flat Andreev bound states appear between point nodes, which leads to double peaks or a single peak in the surface density of states, respectively. As a result, possible superconducting states can be distinguished by combining bulk and surface measurements.

  7. Design for maximum band-gaps in beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    This paper aims to extend earlier optimum design results for transversely vibrating Bernoulli-Euler beams by determining new optimum band-gap beam structures for (i) different combinations of classical boundary conditions, (ii) much larger values of the orders n and n-1 of adjacent upper and lower...

  8. Analysis of photonic band-gap structures in stratified medium

    DEFF Research Database (Denmark)

    Tong, Ming-Sze; Yinchao, Chen; Lu, Yilong;

    2005-01-01

    Purpose - To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design/methodology/approach - A nu-PSTD method is proposed...

  9. Doping-dependent quasiparticle band structure in cuprate superconductors

    NARCIS (Netherlands)

    Eder, R; Ohta, Y.; Sawatzky, G.A

    1997-01-01

    We present an exact diagonalization study of the single-particle spectral function in the so-called t-t'-t ''-J model in two dimensions. As a key result, we find that hole doping leads to a major reconstruction of the quasiparticle band structure near (pi,0): whereas for the undoped system the quasi

  10. X-Band Photonic Band-Gap Accelerator Structure Breakdown Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Marsh, Roark A.; /MIT /MIT /NIFS, Gifu /JAERI, Kyoto /LLNL, Livermore; Shapiro, Michael A.; Temkin, Richard J.; /MIT; Dolgashev, Valery A.; Laurent, Lisa L.; Lewandowski, James R.; Yeremian, A.Dian; Tantawi, Sami G.; /SLAC

    2012-06-11

    In order to understand the performance of photonic band-gap (PBG) structures under realistic high gradient, high power, high repetition rate operation, a PBG accelerator structure was designed and tested at X band (11.424 GHz). The structure consisted of a single test cell with matching cells before and after the structure. The design followed principles previously established in testing a series of conventional pillbox structures. The PBG structure was tested at an accelerating gradient of 65 MV/m yielding a breakdown rate of two breakdowns per hour at 60 Hz. An accelerating gradient above 110 MV/m was demonstrated at a higher breakdown rate. Significant pulsed heating occurred on the surface of the inner rods of the PBG structure, with a temperature rise of 85 K estimated when operating in 100 ns pulses at a gradient of 100 MV/m and a surface magnetic field of 890 kA/m. A temperature rise of up to 250 K was estimated for some shots. The iris surfaces, the location of peak electric field, surprisingly had no damage, but the inner rods, the location of the peak magnetic fields and a large temperature rise, had significant damage. Breakdown in accelerator structures is generally understood in terms of electric field effects. These PBG structure results highlight the unexpected role of magnetic fields in breakdown. The hypothesis is presented that the moderate level electric field on the inner rods, about 14 MV/m, is enhanced at small tips and projections caused by pulsed heating, leading to breakdown. Future PBG structures should be built to minimize pulsed surface heating and temperature rise.

  11. Subharmonic energy-gap structure and heating effects in superconducting niobium point contacts

    DEFF Research Database (Denmark)

    Flensberg, K.; Hansen, Jørn Bindslev

    1989-01-01

    We present experimental data of the temperature-dependent subharmonic energy-gap structure (SGS) in the current-voltage (I-V) curves of superconducting niobium point contacts. The observed SGS is modified by heating effects. We construct a model of the quasiparticle conductance of metallic...

  12. CeO2 as insulation layer in HTc superconducting multilayer and cross over structures

    NARCIS (Netherlands)

    Wijck, van M.A.A.M.; Verhoeven, M.A.J.; Reuvekamp, E.M.C.M.; Gerritsma, G.J.; Blank, D.H.A.; Rogalla, H.

    1996-01-01

    We present a study of the electrical properties of insulating CeO2 layers in combination with superconducting (Y/Dy) Ba2Cu3O7-delta (RBCO) films over ramps and in crossover structures. CeO2 is frequently used as a buffer layer, or template layer for biepitaxial grain boundary junctions, but can als

  13. Photonic crystal digital alloys and their band structure properties.

    Science.gov (United States)

    Lee, Jeongkug; Kim, Dong-Uk; Jeon, Heonsu

    2011-09-26

    We investigated semi-disordered photonic crystals (PCs), digital alloys, and made thorough comparisons with their counterparts, random alloys. A set of diamond lattice PC digital alloys operating in a microwave regime were prepared by alternately stacking two kinds of sub-PC systems composed of alumina and silica spheres of the same size. Measured transmission spectra as well as calculated band structures revealed that when the digital alloy period is short, band-gaps of the digital alloys are practically the same as those of the random alloys. This study indicates that the concept of digital alloys holds for photons in PCs as well.

  14. QUANTITATIVE ANALYSIS OF BANDED STRUCTURES IN DUAL-PHASE STEELS

    Directory of Open Access Journals (Sweden)

    Benoit Krebs

    2011-05-01

    Full Text Available Dual-Phase (DP steels are composed of martensite islands dispersed in a ductile ferrite matrix, which provides a good balance between strength and ductility. Current processing conditions (continuous casting followed by hot and cold rolling generate 'banded structures' i.e., irregular, parallel and alternating bands of ferrite and martensite, which are detrimental to mechanical properties and especially for in-use properties. We present an original and simple method to quantify the intensity and wavelength of these bands. This method, based on the analysis of covariance function of binary images, is firstly tested on model images. It is compared with ASTM E-1268 standard and appears to be more robust. Then it is applied on real DP steel microstructures and proves to be sufficiently sensitive to discriminate samples resulting from different thermo-mechanical routes.

  15. Competition of superconductivity with the structural transition in M o3S b7

    Science.gov (United States)

    Ye, G. Z.; Cheng, J.-G.; Yan, J.-Q.; Sun, J. P.; Matsubayashi, K.; Yamauchi, T.; Okada, T.; Zhou, Q.; Parker, D. S.; Sales, B. C.; Uwatoko, Y.

    2016-12-01

    Prior to the superconducting transition at Tc≈2.3 K , M o3S b7 undergoes a symmetry-lowering, cubic-to-tetragonal structural transition at Ts=53 K . We have monitored the pressure dependence of these two transitions by measuring the resistivity of M o3S b7 single crystals under various hydrostatic pressures up to 15 GPa. The application of external pressure enhances Tc but suppresses Ts until Pc≈10 GPa , above which a pressure-induced first-order structural transition takes place and is manifested by the phase coexistence in the pressure range 8 ≤P ≤12 GPa . The cubic phase above 12 GPa is also found to be superconducting with a higher Tc≈6 K that decreases slightly with further increasing pressure. The variations with pressure of Tc and Ts satisfy the Bilbro-McMillan equation, i.e. Tc nTs 1 -n= constant, thus suggesting the competition of superconductivity with the structural transition that has been proposed to be accompanied with a spin-gap formation at Ts. Our first-principles calculations suggest the importance of magnetism that competes with the superconductivity in M o3S b7 .

  16. From lattice Hamiltonians to tunable band structures by lithographic design

    Science.gov (United States)

    Tadjine, Athmane; Allan, Guy; Delerue, Christophe

    2016-08-01

    Recently, new materials exhibiting exotic band structures characterized by Dirac cones, nontrivial flat bands, and band crossing points have been proposed on the basis of effective two-dimensional lattice Hamiltonians. Here, we show using atomistic tight-binding calculations that these theoretical predictions could be experimentally realized in the conduction band of superlattices nanolithographed in III-V and II-VI semiconductor ultrathin films. The lithographed patterns consist of periodic lattices of etched cylindrical holes that form potential barriers for the electrons in the quantum well. In the case of honeycomb lattices, the conduction minibands of the resulting artificial graphene host several Dirac cones and nontrivial flat bands. Similar features, but organized in different ways, in energy or in k -space are found in kagome, distorted honeycomb, and Lieb superlattices. Dirac cones extending over tens of meV could be obtained in superlattices with reasonable sizes of the lithographic patterns, for instance in InAs/AlSb heterostructures. Bilayer artificial graphene could be also realized by lithography of a double quantum-well heterostructure. These new materials should be interesting for the experimental exploration of Dirac-based quantum systems, for both fundamental and applied physics.

  17. Superconductivity and superconductive electronics

    Science.gov (United States)

    Beasley, M. R.

    1990-12-01

    The Stanford Center for Research on Superconductivity and Superconductive Electronics is currently focused on developing techniques for producing increasingly improved films and multilayers of the high-temperature superconductors, studying their physical properties and using these films and multilayers in device physics studies. In general the thin film synthesis work leads the way. Once a given film or multilayer structure can be made reasonably routinely, the emphasis shifts to studying the physical properties and device physics of these structures and on to the next level of film quality or multilayer complexity. The most advanced thin films synthesis work in the past year has involved developing techniques to deposit a-axis and c-axis YBCO/PBCO superlattices and related structures. The in-situ feature is desirable because no solid state reactions with accompanying changes in volume, morphology, etc., that degrade the quality of the film involved.

  18. Comprehensive studies for the crystal structures and electronic properties of the superconducting system Fe1 + δSe1 - xTex with \\delta \\simeq 0.037 and x \\simeq 0.55

    Science.gov (United States)

    Onoda, Masashige; Kawasaki, Yasuna; Tsubokawa, Masashi; Koyano, Tamotsu

    2010-12-01

    Structural aspects and electronic properties for the Fe1 + δSe1 - xTex system with 0.04 125Te. The crystal structures with an excess Fe site are refined precisely with obvious constraints. For the superconducting composition, the transport properties are explained in terms of the two-band model, where an electron carrier band gives a linear-in-T resistivity and another hole band leads to nearly temperature-independent behaviour. The magnetic susceptibility and the Knight shift are explained with the idea that the electron correlation is enhanced with increasing x and it is reduced with annealing. The spin-lattice relaxation rates for the normal state that show the apparent Korringa relation may also be understood in this framework. These evidences suggest that the superconductivity may emerge in a regime where the correlation is relatively weak in this system.

  19. Development of X-band accelerating structures for high gradients

    Institute of Scientific and Technical Information of China (English)

    S. Bini; M. G. Grimaldi; L. Romano; F. Ruffino; R. Parodi; V. Chimenti; A. Marcelli; L. Palumbo; B. Spataro; V. A. Dolgashev; S. Tantawi; A.D. Yeremian; Y. Higashi

    2012-01-01

    Short copper standing wave (SW) structures operating at an X-band frequency have been recently designed and manufactured at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) using the vacuum brazing technique.High power tests of the structures have been performed at the SLAC National Accelerator Laboratory.In this manuscript we report the results of these tests and the activity in progress to enhance the high gradient performance of the next generation of structures,particularly the technological characterization of high performance coatings obtained via molybdenum sputtering.

  20. Engineering Design of a Multipurpose X-band Accelerating Structure

    CERN Document Server

    Gudkov, Dmitry; Samoshkin, Alexander; Zennaro, Riccardo; Dehler, Micha; Raguin, Jean-Yves

    2010-01-01

    Both FEL projects, SwissFEL and Fermi-Elettra each require an X-band RF accelerating structure for optimal bunch compression at the respective injectors. As the CLIC project is pursuing a program for producing and testing the X-band high-gradient RF structures, a collaboration between PSI, Elettra and CERN has been established to build a multipurpose X-band accelerating structure. This paper focuses on its engineering design, which is based on the disked cells jointed together by diffusion bonding. Vacuum brazing and laser beam welding is used for auxiliary components. The accelerating structure consists of two coupler subassemblies, 73 disks and includes a wakefield monitor and diagnostic waveguides. The engineering study includes the external cooling system, consisting of two parallel cooling circuits and an RF tuning system, which allows phase advance tuning of the cell by deforming the outer wall. The engineering solution for the installation and sealing of the wake field monitor feed-through devices that...

  1. Europium-based iron pnictides: a unique laboratory for magnetism, superconductivity and structural effects

    Science.gov (United States)

    Zapf, Sina; Dressel, Martin

    2017-01-01

    Despite decades of intense research, the origin of high-temperature superconductivity in cuprates and iron-based compounds is still a mystery. Magnetism and superconductivity are traditionally antagonistic phenomena; nevertheless, there is basically no doubt left that unconventional superconductivity is closely linked to magnetism. But this is not the whole story; recently, also structural effects related to the so-called nematic phase gained considerable attention. In order to obtain more information about this peculiar interplay, systematic material research is one of the most important attempts, revealing from time to time unexpected effects. Europium-based iron pnictides are the latest example of such a completely paradigmatic material, as they display not only spin-density-wave and superconducting ground states, but also local Eu2+ magnetism at a similar temperature scale. Here we review recent experimental progress in determining the complex phase diagrams of europium-based iron pnictides. The conclusions drawn from the observations reach far beyond these model systems. Thus, although europium-based iron pnictides are very peculiar, they provide a unique platform to study the common interplay of structural-nematic, magnetic and electronic effects in high-temperature superconductors.

  2. Europium-based iron pnictides: a unique laboratory for magnetism, superconductivity and structural effects.

    Science.gov (United States)

    Zapf, Sina; Dressel, Martin

    2017-01-01

    Despite decades of intense research, the origin of high-temperature superconductivity in cuprates and iron-based compounds is still a mystery. Magnetism and superconductivity are traditionally antagonistic phenomena; nevertheless, there is basically no doubt left that unconventional superconductivity is closely linked to magnetism. But this is not the whole story; recently, also structural effects related to the so-called nematic phase gained considerable attention. In order to obtain more information about this peculiar interplay, systematic material research is one of the most important attempts, revealing from time to time unexpected effects. Europium-based iron pnictides are the latest example of such a completely paradigmatic material, as they display not only spin-density-wave and superconducting ground states, but also local Eu(2+) magnetism at a similar temperature scale. Here we review recent experimental progress in determining the complex phase diagrams of europium-based iron pnictides. The conclusions drawn from the observations reach far beyond these model systems. Thus, although europium-based iron pnictides are very peculiar, they provide a unique platform to study the common interplay of structural-nematic, magnetic and electronic effects in high-temperature superconductors.

  3. Structural, electronic, superconducting and mechanical properties of ReC and TcC

    Energy Technology Data Exchange (ETDEWEB)

    Kavitha, M.; Priyanga, G. Sudha; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com; Santhosh, M. [Department of Physics, N.M.S.S.V.N College, Madurai, Tamilnadu-625019 (India)

    2015-06-24

    The structural, electronic, superconducting and mechanical properties of ReC and TcC are investigated using density functional theory calculations. The lattice constants, bulk modulus, and the density of states are obtained. The calculated lattice parameters are in good agreement with the available results. The density of states reveals that ReC and TcC exhibit metallic behavior at ambient condition. A pressure-induced structural phase transition is observed in both materials.

  4. Structural, electronic, superconducting and mechanical properties of ReC and TcC

    Science.gov (United States)

    Kavitha, M.; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Santhosh, M.

    2015-06-01

    The structural, electronic, superconducting and mechanical properties of ReC and TcC are investigated using density functional theory calculations. The lattice constants, bulk modulus, and the density of states are obtained. The calculated lattice parameters are in good agreement with the available results. The density of states reveals that ReC and TcC exhibit metallic behavior at ambient condition. A pressure-induced structural phase transition is observed in both materials.

  5. Tuning the electronic and the crystalline structure of LaBi by pressure: From extreme magnetoresistance to superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Tafti, F. F.; Torikachvili, M. S.; Stillwell, R. L.; Baer, B.; Stavrou, E.; Weir, S. T.; Vohra, Y. K.; Yang, H. -Y.; McDonnell, E. F.; Kushwaha, S. K.; Gibson, Q. D.; Cava, R. J.; Jeffries, J. R.

    2017-01-01

    Extreme magnetoresistance (XMR) in topological semimetals is a recent discovery which attracts attention due to its robust appearance in a growing number of materials. To search for a relation between XMR and superconductivity, we study the effect of pressure on LaBi. By increasing pressure, we observe the disappearance of XMR followed by the appearance of superconductivity at P ≈ 3.5 GPa. We find a region of coexistence between superconductivity and XMR in LaBi in contrast to other superconducting XMR materials. The suppression of XMR is correlated with increasing zero-field resistance instead of decreasing in-field resistance. At higher pressures, P ≈ 11 GPa, we find a structural transition from the face-centered cubic lattice to a primitive tetragonal lattice, in agreement with theoretical predictions. The relationship between extreme magnetoresistance, superconductivity, and structural transition in LaBi is discussed.

  6. Parameterization and algebraic structure of 3-band orthogonal wavelet systems

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In this paper, a complete parameterization for the 3-band compact wavelet systems is presented. Using the parametric result, a program of the filterbank design is completed, which can give not only the filterbanks but also the graphs of all possible scaling functions and their corresponding wavelets. Especially some symmetric wavelets with small supports are given. Finally an algebraic structure for this kind of wavelet systems is characterized.

  7. Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr

    Directory of Open Access Journals (Sweden)

    Kazuhiko Kuroki

    2008-01-01

    Full Text Available We investigate the possibility of realizing unconventional superconductivity in doped band insulators on the square and honeycomb lattices. The latter lattice is found to be a good candidate due to the disconnectivity of the Fermi surface. We propose applying the theory to the superconductivity in doped layered nitride β-MNCl (M= Hf, Zr. Finally, we compare two groups of superconductors with disconnected Fermi surface, β-MNCl and the iron pnictides, which have high critical temperature Tc, despite some faults against superconductivity are present.

  8. Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr).

    Science.gov (United States)

    Kuroki, Kazuhiko

    2008-12-01

    We investigate the possibility of realizing unconventional superconductivity in doped band insulators on the square and honeycomb lattices. The latter lattice is found to be a good candidate due to the disconnectivity of the Fermi surface. We propose applying the theory to the superconductivity in doped layered nitride β-MNCl (M= Hf, Zr). Finally, we compare two groups of superconductors with disconnected Fermi surface, β-MNCl and the iron pnictides, which have high critical temperature Tc, despite some faults against superconductivity are present.

  9. Giant Mesoscopic Fluctuations and Long-Range Superconducting Correlations in Superconductor-Ferromagnet Structures.

    Science.gov (United States)

    Mel'nikov, A S; Buzdin, A I

    2016-08-12

    The fluctuating superconducting correlations emerging in dirty hybrid structures under the conditions of the strong proximity effect are demonstrated to affect the validity range of the widely used formalism of Usadel equations at mesoscopic scales. In superconductor-ferromagnet structures these giant mesoscopic fluctuations originating from the interference effects for the Cooper pair wave function in the presence of the exchange field can be responsible for an anomalously slow decay of superconducting correlations in a ferromagnet even when the noncollinear and spin-orbit effects are negligible. The resulting sample-to-sample fluctuations of the Josephson current in superconductor-ferromagnetic-superconductor junctions and the local density of states in superconductor-ferromagnetic hybrid structures can provide an explanation of the long-range proximity phenomena observed in mesoscopic samples with collinear magnetization.

  10. Ferromagnetic/superconducting bilayer structure: A model system for spin diffusion length estimation

    CERN Document Server

    Soltan, S; Habermeier, H U

    2004-01-01

    We report detailed studies on ferromagnet--superconductor bilayer structures. Epitaxial bilayer structures of half metal--colossal magnetoresistive La$_{\\mathrm{2/3}}$Ca$_{\\mathrm{1/3}}$MnO$_{\\mathrm{3}}$ (HM--CMR) and high--$T_{\\mathrm{c}}$ superconducting YBa$_{\\mathrm{2}}$Cu$_{\\mathrm{3}}$O$_{\\mathrm{7-\\delta}}$(HTSC) are grown on SrTiO$_3$ (100) single--crystalline substrates using pulsed laser deposition. Magnetization $M$(T) measurements show the coexistence of ferromagnetism and superconductivity in these structures at low temperatures. Using the HM--CMR layer as an electrode for spin polarized electrons, we discuss the role of spin polarized self injection into the HTSC layer. The experimental results are in good agreement with a presented theoretical estimation, where the spin diffusion length $\\xi_{\\mathrm {FM}}$ is found to be in the range of $\\xi_{\\mathrm{FM}} \\approx$ 10 nm.

  11. RVB states in doped band insulators from Coulomb forces: theory and a case study of superconductivity in BiS2 layers

    Science.gov (United States)

    Baskaran, G.

    2016-12-01

    Doped band insulators, HfNCl, WO3, diamond, Bi2Se3, BiS2 families, STO/LAO interface, gate doped SrTiO3, MoS2 and so on are unusual superconductors. With an aim to build a general theory for superconductivity in doped band insulators, we focus on the BiS2 family which was discovered by Mizuguchi et al in 2012. While maximum Tc is only ˜11 K in {{LaO}}1-{{x}}{{{F}}}{{x}}{{BiS}}2, a number of experimental results are puzzling and anomalous in the sense that they resemble high T c and unconventional superconductors. Using a two orbital model of Usui, Suzuki and Kuroki, we show that the uniform low density free Fermi sea in {{LaO}}{0,5}{{{F}}}0.5{{BiS}}2 is unstable towards formation of the next nearest neighbor Bi-S-Bi diagonal valence bond (charged -2e Cooper pair) and their Wigner crystallization. Instability to this novel state of matter is caused by unscreened nearest neighbor coulomb repulsions (V ˜ 1 eV) and a hopping pattern with sulfur mediated diagonal next nearest neighbor Bi-S-Bi hopping t’ ˜ 0.88 eV, as well as larger than nearest neighbor Bi-Bi hopping, t ˜ 0.16 eV. Wigner crystals of Cooper pairs quantum melt for doping around x = 0.5 and stabilize certain resonating valence bond states and superconductivity. We study a few variational RVB states and suggest that BiS2 family members are latent high Tc superconductors, but challenged by competing orders and the fragile nature of many body states sustained by unscreened Coulomb forces. One of our superconducting states has d XY symmetry and a gap. We also predict a 2d Bose metal or vortex liquid normal state, as charged -2e valence bonds survive in the normal state.

  12. Influence of calcium on transport properties, band spectrum and superconductivity of YBa2Cu3O(y) and YBa(1.5)La(0.5)Cu3O(y)

    Science.gov (United States)

    Gasumyants, V. E.; Vladimirskaya, E. V.; Patrina, I. B.

    1995-01-01

    The comparative investigation of transport phenomena in Y(1-x)Ca(x)Ba2Cu3O(y) (0 is less than x is less than 0.25; 6.96 is greater than y is greater than 6.87 and 6.73 is less than x is less than 6.53); Y(1-x)Ca(x)Ba(1.5)La(0.5)Cu3O(y) (0 is less than x is less than 0.5; 7.12 is greater than y is greater than 6.96) and YBa(2-x)La(x)Cu3O(y) (0 is less than x is less than 0.5; 6.95 is less than y is less than 7.21) systems have been carried out. The temperature dependencies of resistivity and thermopower have been measured. It was found that the S(T) dependencies take some additional features with Ca content increase. The results obtained have been analyzed on the basis of the phenomenological theory of electron transport in the case of the narrow conductive band. The main parameters of the band spectrum (the band filling with electrons degree and the total effective band width) have been determined. The dependencies of these from contents of substituting elements are discussed. Analyzing the results obtained simultaneously with the tendencies in oxygen content and critical temperature change we have confirmed the conclusion that the oxygen sublattice disordering has a determinant effect on band structure parameters and superconductive properties of YBa2Cu3O(y). The results obtained suggest that Ca gives rise to some peculiarities in band spectrum of this compound.

  13. Electronic structure and superconductivity of multi-layered organic charge transfer salts

    Energy Technology Data Exchange (ETDEWEB)

    Jeschke, Harald O.; Altmeyer, Michaela; Guterding, Daniel; Valenti, Roser [Institut fuer Theoretische Physik, Goethe-Universitaet Frankfurt, 60438 Frankfurt (Germany)

    2015-07-01

    We examine the electronic properties of polymorphs of (BEDT-TTF){sub 2}Ag(CF{sub 3}){sub 4}(TCE) (1,1,2-trichloroethane) within density functional theory (DFT). While a phase with low superconducting transition temperature T{sub c}=2.6 K exhibits a κ packing motif, two high T{sub c} phases are layered structures consisting of α{sup '} and κ packed layers. We determine the electronic structures and discuss the influence of the insulating α{sup '} layer on the conducting κ layer. In the κ-α{sub 1}{sup '} dual-layered compound, we find that the stripes of high and low charge in the α{sup '} layer correspond to a stripe pattern of hopping parameters in the κ layer. Based on the different underlying Hamiltonians, we study the superconducting properties and try to explain the differences in T{sub c}.

  14. Crossing points in the electronic band structure of vanadium oxide

    Directory of Open Access Journals (Sweden)

    Keshav N. Shrivastava

    2010-03-01

    Full Text Available The electronic band structures of several models of vanadium oxide are calculated. In the models 1-3, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 4 vanadium atoms. In model 1, a=b=c 2.3574 Å; in model 2, a= 4.7148 Å, b= 2.3574 Å and c= 2.3574 Å; and in model 3, a= 4.7148 Å, b= 2.3574 Å and c= 4.7148 Å. In the models 4-6, every vanadium atom is connected to 4 oxygen atoms and every oxygen atom is connected to 2 vanadium atoms. In model 4, a=b= 4.551 Å and c= 2.851 Å; in model 5, a=b=c= 3.468 Å; and in model 6, a=b=c= 3.171 Å. We have searched for a crossing point in the band structure of all the models. In model 1 there is a point at which five bands appear to meet but the gap is 7.3 meV. In model 2 there is a crossing point between G and F points and there is a point between F and Q with the gap ≈ 3.6608 meV. In model 3, the gap is very small, ~ 10-5 eV. In model 4, the gap is 5.25 meV. In model 5, the gap between Z and G points is 2.035 meV, and in model 6 the gap at Z point is 4.3175 meV. The crossing point in model 2 looks like one line is bent so that the supersymmetry is broken. When pseudopotentials are replaced by a full band calculation, the crossing point changes into a gap of 2.72 x 10-4 eV.

  15. Chemically gated electronic structure of a superconducting doped topological insulator system

    Science.gov (United States)

    Wray, L. A.; Xu, S.; Neupane, M.; Fedorov, A. V.; Hor, Y. S.; Cava, R. J.; Hasan, M. Z.

    2013-07-01

    Angle resolved photoemission spectroscopy is used to observe changes in the electronic structure of bulk-doped topological insulator CuxBi2Se3 as additional copper atoms are deposited onto the cleaved crystal surface. Carrier density and surface-normal electrical field strength near the crystal surface are estimated to consider the effect of chemical surface gating on atypical superconducting properties associated with topological insulator order, such as the dynamics of theoretically predicted Majorana Fermion vortices.

  16. Enhanced Superconductivity in Close Proximity to the Structural Phase Transition of Sr1-xBaxNi2P2

    Science.gov (United States)

    Kudo, Kazutaka; Kitahama, Yutaka; Iba, Keita; Takasuga, Masaya; Nohara, Minoru

    2017-03-01

    The structural evolution and superconductivity of a 122-type solid solution Sr1-xBaxNi2P2 were studied. We found that an orthorhombic-tetragonal structural phase transition takes place at x = 0.5, and is characterized by the P-P dimers breaking. The superconducting transition temperature exhibited its highest value of 2.85 K at x = 0.4.

  17. Synthesis, physical properties and band structure of non-magnetic Y3AlC

    Science.gov (United States)

    Ghule, S. S.; Garde, C. S.; Ramakrishnan, S.; Singh, S.; Rajarajan, A. K.; Laad, Meena

    2016-10-01

    Y3AlC has been synthesized by arc melting and subsequent annealing. Rietveld analysis of the powder x-ray diffraction (XRD) data confirms cubic Pm-3m structure. Electrical resistivity (ρ) of Y3AlC exhibits metallic behaviour. No sign of superconductivity is observed down to the lowest measurement temperatures of 4.2 K in ρ, and 2 K in magnetic susceptibility (χ) and specific heat (Cp) measurements. The value of the electronic specific heat coefficient γ is 1.36 mJ/K2 mol from which the density of states (DOS) at the Fermi energy (EF) is obtained as 0.57 states/eV.unit cell. The value of Debye temperature θD is estimated to be 315 K. Electronic band structure calculations of Y3AlC reveal a pseudo-gap in the DOS at EF leading to a small value of 0.5 states/eV unit cell which matches quite well with that obtained from γ. Non-zero value of the DOS indicates metallic behaviour as confirmed by our ρ data. Covalent and ionic bonding seem to co-exist with metallic bonding in Y3AlC as indicated by van Arkel- Ketelaar triangle for Zintl-like systems.

  18. Wakefield Monitor Experiments with X-Band Accelerating Structures

    CERN Document Server

    Lillestøl, Reidar; Corsini, Roberto; Döbert, Steffen; Farabolini, Wilfrid; Malina, Lukas; Pfingstner, Juergen; Wuensch, Walter

    2015-01-01

    The accelerating structures for CLIC must be aligned with a precision of a few um with respect to the beam trajectory in order to mitigate emittance growth due to transverse wake fields. We report on first results from wake field monitor tests in an X-band structure, with a probe beam at the CLIC Test Facility. The monitors are currently installed in the CLIC Two-Beam Module. In order to fully demonstrate the feasibility of using wakefield monitors for CLIC, the precision of the monitors must be verified using a probe beam while simultaneously filling the structure with high power rf used to drive the accelerating mode. We outline plans to perform such a demonstration in the CLIC Test Facility.

  19. Collective Band Structures in Neutron-Rich 108Mo Nucleus

    Institute of Scientific and Technical Information of China (English)

    DING Huai-Bo; WANG Jian-Guo; XU Qiang; ZHU Sheng-Jiang; J. H. Hamilton; A. V. Ramayya; J. K. Hwang; Y. X. Luo; J. O. Rasmussen; I. Y. Lee; CHE Xing-Lai

    2007-01-01

    High spin states in the neutron-rich 108Mo nucleus are studied by measuring prompt γ-rays following the spontaneous fission of 252Cf with a Gammasphere detector array. The ground-state band is confirmed, and the one-phonon γ-vibrational band is updated with spin up to 12 h. A new collective band with the band head level at 1422.4 keV is suggested as a two-phonon γ-vibrational band. Another new band is proposed as a two-quasi-proton excitation band. Systematic characteristics of the collective bands are discussed.

  20. Fabrication of band-pass filter using YBCO film at Ka-band frequency; YBCO hakumaku wo mochiita Ka-band taiiki tsuka fuiruta no sakusei

    Energy Technology Data Exchange (ETDEWEB)

    Yoshitake, T.; Hattori, W.; Murakami, S.; Suzuki, S. [NEC Corp., Tokyo (Japan)

    1999-11-10

    In this report, Ka band microstrip band pass filter was produced experimentally using an YBCO system high temperature superconductivity thin film as examination initial stage high temperature superconductivity a thin film superscription communication element. With it, the following were examined: Evaluation method and frequency characteristics of the filter. Especially, the examination on structure of the package and system of measurement using refrigerating machine becomes important in order to evaluate the filter with the high frequency. (NEDO)

  1. Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Zhao; Martin, Michael C.; Kim, P.; Stormer, H.L.; Basov, Dimitri N.

    2008-12-10

    We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.

  2. Electronic band structure of calcium selenide under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Louail, L. [Faculty of Sciences, Department of Physics, University of Setif, Setif (Algeria)], E-mail: llouail@yahoo.fr; Haddadi, K.; Maouche, D.; Ali Sahraoui, F.; Hachemi, A. [Faculty of Sciences, Department of Physics, University of Setif, Setif (Algeria)

    2008-09-01

    Energy band structures under pressure of calcium selenide (CaSe) were calculated using the plane-wave pseudopotential code CASTEP. The results show a progressive transition from a direct to an indirect gap semiconductor at a pressure of about 2 GPa, in the B1 phase. An insulator-conductor change was also observed at 70 GPa, in the B2 phase. Concerning CaSe, these two results could not be evidenced in previous literature. Hence, our work is a first attempt in this direction.

  3. Foreword: Focus on Superconductivity in Semiconductors

    Directory of Open Access Journals (Sweden)

    Yoshihiko Takano

    2008-01-01

    Full Text Available Since the discovery of superconductivity in diamond, much attention has been given to the issue of superconductivity in semiconductors. Because diamond has a large band gap of 5.5 eV, it is called a wide-gap semiconductor. Upon heavy boron doping over 3×1020 cm−3, diamond becomes metallic and demonstrates superconductivity at temperatures below 11.4 K. This discovery implies that a semiconductor can become a superconductor upon carrier doping. Recently, superconductivity was also discovered in boron-doped silicon and SiC semiconductors. The number of superconducting semiconductors has increased. In 2008 an Fe-based superconductor was discovered in a research project on carrier doping in a LaCuSeO wide-gap semiconductor. This discovery enhanced research activities in the field of superconductivity, where many scientists place particular importance on superconductivity in semiconductors.This focus issue features a variety of topics on superconductivity in semiconductors selected from the 2nd International Workshop on Superconductivity in Diamond and Related Materials (IWSDRM2008, which was held at the National Institute for Materials Science (NIMS, Tsukuba, Japan in July 2008. The 1st workshop was held in 2005 and was published as a special issue in Science and Technology of Advanced Materials (STAM in 2006 (Takano 2006 Sci. Technol. Adv. Mater. 7 S1.The selection of papers describe many important experimental and theoretical studies on superconductivity in semiconductors. Topics on boron-doped diamond include isotope effects (Ekimov et al and the detailed structure of boron sites, and the relation between superconductivity and disorder induced by boron doping. Regarding other semiconductors, the superconducting properties of silicon and SiC (Kriener et al, Muranaka et al and Yanase et al are discussed, and In2O3 (Makise et al is presented as a new superconducting semiconductor. Iron-based superconductors are presented as a new series of high

  4. Tests of a niobium split-ring superconducting heavy ion accelerating structure

    Energy Technology Data Exchange (ETDEWEB)

    Benaroya, R.; Bollinger, L.M.; Jaffey, A.H.; Khoe, T.K.; Olesen, M.C.; Scheibelhut, C.H.; Shepard, K.W.; Wesolowski, W.A.

    1976-01-01

    A niobium split-ring accelerating structure designed for use in the Argonne superconducting heavy-ion energy booster was successfully tested. The superconducting resonator has a resonant frequency of 97 MHz and an optimum particle velocity ..beta.. = 0.11. Ultimate performance is expected to be limited by peak surface fields, which in this structure are 4.7 E/sub a/ electric and 170 E/sub a/ (Gauss) magnetic, where E/sub a/ is the effective accelerating gradient in MV/m. The rf losses in two demountable superconducting joints severely limited performance in initial tests. Following independent measurements of the rf loss properties of several types of demountable joints, one demountable joint was eliminated and the other modified. Subsequently, the resonator could be operated continuously at E/sub a/ = 3.6 MV/m (corresponding to an energy gain of 1.3 MeV per charge) with 10W rf input power. Maximum field level was limited by electron loading. The mechanical stability of the resonator under operating conditions is excellent: vibration induced eigenfrequency noise is less than 120 Hz peak to peak, and the radiation pressure induced frequency shift is ..delta..f/f = 1.6 x 10/sup -6/ E/sub a//sup 2/.

  5. Latest Development in Superconducting RF Structures for beta=1 Particle Acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Peter Kneisel

    2006-06-26

    Superconducting RF technology is since nearly a decade routinely applied to different kinds of accelerating devices: linear accelerators, storage rings, synchrotron light sources and FEL's. With the technology recommendation for the International Linear Collider (ILC) a year ago, new emphasis has been placed on improving the performance of accelerating cavities both in Q-value and in accelerating gradients with the goal to achieve performance levels close to the fundamental limits given by the material parameters of the choice material, niobium. This paper will summarize the challenges to SRF technology and will review the latest developments in superconducting structure design. Additionally, it will give an overview of the newest results and will report on the developments in alternative materials and technologies.

  6. The effects of Ag, Mg, and Pr doping on the superconductivity and structure of BSCCO

    Science.gov (United States)

    Boussouf, N.; Mosbah, M.-F.; Guerfi, T.; Bouaïcha, F.; Chamekh, S.; Amira, A.

    2009-11-01

    The influence of Ag, Mg, and Pr additions and co-additions on microstructure and phase formation of Bi2Sr2CaCu2O8+d (Bi2212) system is investigated. Polycrystalline Bi2212 samples were synthesized in air by solid state reaction method. Phase analysis, micro structural observations and magnetic properties were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and A.C. susceptibility measurements respectively. XRD results reveal two main phases (Bi-2201 and Bi2212). SEM photographs show that the substitution by Ag, Mg or Pr affects the mechanism of the grains growth. The undoped sample has a critical temperature Tc of 65 K while in the Mg and Ag containing compounds the Tc is 77 K and 75 K respectively. The Pr containing compound exhibits no superconductivity. A valence of the Pr ion higher than 3+ in the lattice supports the holefilling mechanism of the suppression of superconductivity.

  7. Entangled States in a Single-Qubit Structure with SQUID Coupled with a Super-conducting Resonator

    Institute of Scientific and Technical Information of China (English)

    SONG Jian-Wen; LIANG Bao-Long; HAI Wen-Hua; WANG Ji-Suo; ZHONG Hong-Hua; MENG Xiang-Guo; LUO Xiao-Bing

    2008-01-01

    In this paper, the number-phase quantization scheme of the mesoscopic circuit, which consists of a single-qubit structure with superconducting quantum interference device coupled with a super-conducting resonator, is given. By introducing a unitary matrix and by means of spectral decomposition, the Hamiltonian operator of the system is exactly formulated in compact forms in spin-1/2 notation. The eigenvalues and the eigenstates of the system are investigated. It is found that using this system the entangled states can not only be prepared, but also be manipulated by tuning the magnetic flux through the super-conducting loop.

  8. Subharmonic energy-gap structure in superconducting weak links

    DEFF Research Database (Denmark)

    Flensberg, K.; Hansen, Jørn Bindslev; Octavio, M.

    1988-01-01

    We present corrected calculations of the subharmonic energy-gap structure using the model of Octavio, Tinkham, Blonder, and Klapwijk, which includes the effect of normal scattering in the weak link. We show that while the overall predictions of this model do not change qualitatively, the details ...

  9. Optical Properties of One-dimensional Three-component Photonic Band Gap Structure

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Theoretical study of the optical properties of one-dimensional three-component photonic band gap structure, which is composed of three alternating dielectric layers of different refractive indices and thickness in a unit cell, is performed. This one-dimensional photonic band gap structure exhibits the transparency band and forbidden band. We find that there are several mini-bands of the allowed transmission to be created within the photonic band gap region of the structure if a defect designed specially is introduced inside the structure. This characteristic is very important for some practical applications.

  10. Calculation of band structure in (101)-biaxially strained Si

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of(101)-biaxially strained Si on relaxed Si1-X GeX alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys(-4) splitting from the [0±10] valley(-2) constitute the conduction b0and(CB) edge,that valence band(VB) edge degeneracy is partially lifted and that the electron mass is un-altered under strain while the hole mass decreases in the [100] and [010] directions. In addition,the fitted dependences of CB splitting energy,VB splitting energy and indirect bandgap on X are all linear.

  11. Local structural distortions and their role in superconductivity in SmFeAsO1-xFx superconductors

    Science.gov (United States)

    Ingle, Kapil; Priolkar, K. R.; Pal, Anand; Awana, V. P. S.; Emura, S.

    2014-07-01

    EXAFS studies at the As K edge as a function of temperature were carried out in SmFeAsO1-xFx (x = 0 and 0.2) compounds to understand the role of local structural distortions in superconductivity observed in F-doped compounds. A significant correlation between the thermal variation of local structural parameters such as anion height and superconducting onset is found in the fluorinated compounds. Such a variation in anion height is absent in the non-superconducting compound. An increase in the Fe-As bond distance just below the superconducting onset temperature indicates a similarity between the distortions observed in the high-T_{C} cuprates and these Fe-based superconductors.

  12. Fast Chopper Structure for the CERN Superconducting Proton Linac

    CERN Document Server

    Caspers, Friedhelm; Kurennoy, S S

    2002-01-01

    The SPL chopper is a travelling wave device, which deflects a slow beam (b = v/c = 0.08) by its transverse electric field. We discuss the chopper deflecting structure based on a meander line printed on an alumina substrate. This concept profits from the radiation resistance of alumina, its excellent out-gassing properties and its good thermal conductivity. The use of well established MIC (microwave integrated circuit) thick film technology allows easy implementation of prototypes; the thickness of the printed layer should be increased by means of an electrochemical deposition method. The topology of the structure has been chosen from standard MIC layouts and was subsequently optimized using numerical simulations. Several prototypes have been manufactured and measurements have shown encouraging results.

  13. Electrical and structural properties of the YBCO superconducting-semiconducting interface

    Energy Technology Data Exchange (ETDEWEB)

    Sobolewski, R. (Dept. of Electrical Engineering and Lab. for Laser Energetics, Univ. of Rochester, NY (United States) Inst. of Physics, Polish Academy of Sciences, Warszawa (Poland)); Xiong, W. (Dept. of Electrical Engineering and Lab. for Laser Energetics, Univ. of Rochester, NY (United States)); Kula, W. (Dept. of Electrical Engineering and Lab. for Laser Energetics, Univ. of Rochester, NY (United States) Inst. of Physics, Polish Academy of Sciences, Warszawa (Poland)); McIntyre, B. (Inst. of Optics, Univ. of Rochester, NY (United States))

    1994-02-01

    We report our studies on electrical and structural properties of an interface between the oxygen-poor (semiconducting) and oxygen-rich (superconducting, T[sub c] = 89.5 K) YBa[sub 2]Cu[sub 3]O[sub y]. Our thin-film test structures were fully monolithic and prepared by a laser-writing patterning technique. Scanning electron and optical microscopy measurements revealed that the interface was very sharp (<1 [mu]m wide) and did not smear over the period of several months. Electrical measurements of the interface showed completely linear current-voltage characteristics in the tested temperature range between 77 and 300 K. (orig.)

  14. Numerical analysis of the superconducting magnet outer vessel of a Maglev train by a structural and electromagnetic coupling method

    Science.gov (United States)

    Matsue, H.; Demachi, K.; Miya, K.

    2001-09-01

    The harmonic magnetic field generated by the ground coils can cause vibration of the superconducting magnet, which must be reduced as it generates heat in the liquid helium temperature range. Therefore, it is important for the design of lighter magnets to exactly estimate the electromagnetic force on the superconducting magnet. Some causes of the vibration were analyzed by the structural and electromagnetic coupling FEM-BEM method.

  15. Structure of negative parity yrast bands in odd mass 125-131Ce nuclei

    Indian Academy of Sciences (India)

    Arun Bharti; Suram Singh; S K Khosa

    2010-04-01

    The negative parity yrast bands of neutron-deficient 125-131Ce nuclei are studied by using the projected shell model approach. Energy levels, transition energies and (1)/(2) ratios are calculated and compared with the available experimental data. The calculations reproduce the band-head spins of negative parity yrast bands and indicate the multi-quasiparticle structure for these bands.

  16. Imaging of current distributions in superconducting thin film structures; Abbildung von Stromverteilungen in supraleitenden Duennfilmstrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Doenitz, D.

    2006-10-31

    Local analysis plays an important role in many fields of scientific research. However, imaging methods are not very common in the investigation of superconductors. For more than 20 years, Low Temperature Scanning Electron Microscopy (LTSEM) has been successfully used at the University of Tuebingen for studying of condensed matter phenomena, especially of superconductivity. In this thesis LTSEM was used for imaging current distributions in different superconducting thin film structures: - Imaging of current distributions in Josephson junctions with ferromagnetic interlayer, also known as SIFS junctions, showed inhomogeneous current transport over the junctions which directly led to an improvement in the fabrication process. An investigation of improved samples showed a very homogeneous current distribution without any trace of magnetic domains. Either such domains were not present or too small for imaging with the LTSEM. - An investigation of Nb/YBCO zigzag Josephson junctions yielded important information on signal formation in the LTSEM both for Josephson junctions in the short and in the long limit. Using a reference junction our signal formation model could be verified, thus confirming earlier results on short zigzag junctions. These results, which could be reproduced in this work, support the theory of d-wave symmetry in the superconducting order parameter of YBCO. Furthermore, investigations of the quasiparticle tunneling in the zigzag junctions showed the existence of Andreev bound states, which is another indication of the d-wave symmetry in YBCO. - The LTSEM study of Hot Electron Bolometers (HEB) allowed the first successful imaging of a stable 'Hot Spot', a self-heating region in HEB structures. Moreover, the electron beam was used to induce an - otherwise unstable - hot spot. Both investigations yielded information on the homogeneity of the samples. - An entirely new method of imaging the current distribution in superconducting interference

  17. Atomic and electronic structures evolution of the narrow band gap semiconductor Ag2Se under high pressure

    Science.gov (United States)

    Naumov, P.; Barkalov, O.; Mirhosseini, H.; Felser, C.; Medvedev, S. A.

    2016-09-01

    Non-trivial electronic properties of silver telluride and other chalcogenides, such as the presence of a topological insulator state, electronic topological transitions, metallization, and the possible emergence of superconductivity under pressure have attracted attention in recent years. In this work, we studied the electronic properties of silver selenide (Ag2Se). We performed direct current electrical resistivity measurements, in situ Raman spectroscopy, and synchrotron x-ray diffraction accompanied by ab initio calculations to explore pressure-induced changes to the atomic and electronic structure of Ag2Se. The temperature dependence of the electrical resistivity was measured up to 30 GPa in the 4-300 K temperature interval. Resistivity data showed an unusual increase in the thermal energy gap of phase I, which is a semiconductor under ambient conditions. Recently, a similar effect was reported for the 3D topological insulator Bi2Se3. Raman spectroscopy studies revealed lattice instability in phase I indicated by the softening of observed vibrational modes with pressure. Our hybrid functional band structure calculations predicted that phase I of Ag2Se would be a narrow band gap semiconductor, in accordance with experimental results. At a pressure of ~7.5 GPa, Ag2Se underwent a structural transition to phase II with an orthorhombic Pnma structure. The temperature dependence of the resistivity of Ag2Se phase II demonstrated its metallic character. Ag2Se phase III, which is stable above 16.5 GPa, is also metallic according to the resistivity data. No indication of the superconducting transition is found above 4 K in the studied pressure range.

  18. Structure, texture, and properties of superconductive electrolytic niobium coatings on glassy carbon

    Science.gov (United States)

    Kolosov, V. N.; Shevyrev, A. A.

    2016-01-01

    Superconductive electrolytic niobium coatings 0.1-100 μm thick are prepared via electrochemical deposition onto SU-2000 glassy carbon substrates in (LiF + NaF + KF)eut-K2NbF7 molten salt. Their structure, texture, and residual stresses are investigated by X-ray diffraction methods. It is shown that, when depositing the coatings, the diffusion superconductive layer of niobium carbide is formed at the substrate-coating interface. The sequence of changes in the axis of the texture of niobium coating from through to a textureless state with an increase in their thickness is established. It is found that, in the interval 0.5-5 μm, the sign of the stress changes (compressive stresses change into tensile stresses) and it reaches its maximum value. With an increase in the coating thickness from 5 to 100 μm, tensile stresses decrease from 345 to 80 MPa. It is shown that the coatings formed can be used as the material for creating a working layer of a superconducting cryogenic gyroscope rotor.

  19. Structural Evolution of a Warm Frontal Precipitation Band During GCPEx

    Science.gov (United States)

    Colle, Brian A.; Naeger, Aaron; Molthan, Andrew; Nesbitt, Stephen

    2015-01-01

    A warm frontal precipitation band developed over a few hours 50-100 km to the north of a surface warm front. The 3-km WRF was able to realistically simulate band development, although the model is somewhat too weak. Band genesis was associated with weak frontogenesis (deformation) in the presence of weak potential and conditional instability feeding into the band region, while it was closer to moist neutral within the band. As the band matured, frontogenesis increased, while the stability gradually increased in the banding region. Cloud top generating cells were prevalent, but not in WRF (too stable). The band decayed as the stability increased upstream and the frontogenesis (deformation) with the warm front weakened. The WRF may have been too weak and short-lived with the band because too stable and forcing too weak (some micro issues as well).

  20. A Brief Introduction to Band Structure in Three Dimensions

    CERN Document Server

    Iannucci, Peter

    2011-01-01

    Without our ability to model and manipulate the band structure of semiconducting materials, the modern digital computer would be impractically large, hot, and expensive. In the undergraduate QM curriculum, we studied the effect of spatially periodic potentials on the spectrum of a charged particle in one dimension. We would like to understand how to extend these methods to model actual crystalline materials. Along the way, we will explore the construction of periodic potentials in three dimensions, and we use this framework to relate the single-particle Hamiltonian to the potential contribution from each atom. We then construct a crude model system analogous to the semiconductor silicon, and demonstrate the appearance of level splitting and band gaps as the strength of the potential is varied, in accordance with our intuition from the one-dimensional case. We discuss refinements of the model to include many-particle effects, and finally we show how a careful choice of the potential function leads to good agre...

  1. A Compact UWB Band-Pass Filter Using Embedded Circular Slot Structures for Improved Upper Stop-band Performance

    DEFF Research Database (Denmark)

    Shen, Ming; Ren, Jian; Mikkelsen, Jan Hvolgaard;

    2016-01-01

    structures into the ring resonator. This is different from conventional designs using cascaded bandstop/low-pass filters for stop-band response suppression, which usually leads to big circuit sizes. And hence the proposed approach can reduce the circuit size significantly. A prototype filter with a compact...... size (13.6 mm×6.75 mm) has been implemented for experimental validation. The measured results show a −3 dB frequency band from 3.4 GHz to 11.7 GHz and > 20 dB upper stop-band suppression from 12.5 GHz to 20GHz....

  2. Band structure systematics and symmetries in even-even nuclei

    Science.gov (United States)

    Bucurescu, D.; Cata-Danil, Gh.; Ivascu, M.; Ur, C. A.

    1993-07-01

    It is shown that the experimental in-band energy ratios for the even-even nuclei obey universal systematics similar to those observed by Mallmann for the quasiground band. Systematic correlations between energy ratios belonging to different bands are also found in certain cases. Finally, correlations between mixed energy ratios are shown to be useful in characterizing the evolution of the nulcear collectivity.

  3. Simulation of electronic structure Hamiltonians in a superconducting quantum computer architecture

    Energy Technology Data Exchange (ETDEWEB)

    Kaicher, Michael; Wilhelm, Frank K. [Theoretical Physics, Saarland University, 66123 Saarbruecken (Germany); Love, Peter J. [Department of Physics, Haverford College, Haverford, Pennsylvania 19041 (United States)

    2015-07-01

    Quantum chemistry has become one of the most promising applications within the field of quantum computation. Simulating the electronic structure Hamiltonian (ESH) in the Bravyi-Kitaev (BK)-Basis to compute the ground state energies of atoms/molecules reduces the number of qubit operations needed to simulate a single fermionic operation to O(log(n)) as compared to O(n) in the Jordan-Wigner-Transformation. In this work we will present the details of the BK-Transformation, show an example of implementation in a superconducting quantum computer architecture and compare it to the most recent quantum chemistry algorithms suggesting a constant overhead.

  4. A Banding Structure in a Ni-Cu-Si Cast Alloy

    Institute of Scientific and Technical Information of China (English)

    Qi ZHENG; Yufeng ZHENG; Hongyu ZHANG; Xiaofeng SUN; Hengrong GUAN; Zhuangqi HU

    2008-01-01

    The solidified microstructure of a Ni-Cu-Si cast alloy has been investigated, and a kind of banding structure was observed. The results showed that, the banding structure was composed of coarser particles which were Ni3Si type of precipitates and similar to the fine particles precipitate uniformly distributed within matrix of Ni solid solution, in both crystal structure and composition. The formation of bandings was resulted from cast thermal stress and dislocation walls. It was found that the cracks propagated along these bandings in tensile test. The banding structure can be depressed by reducing the cast thermal stress, which can improve the Qtensile ductility.

  5. Field Dependence of π-Band Superconducting Gap in MgB2 Thin Films from Point-Contact Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    HUANG Yan; XI Xiao-Xing; WANG Yong-Lei; SHAN Lei; JIA Ying; YANG Huan; WEN Hai-Hu; ZHUANG Cheng-Gang; LI Qi; CUI Yi

    2008-01-01

    We present the results of point-contact spectroscopy measurements on high-quality epitaxial MgB2 thin films with injected current along the c-axis. The temperature and field dependences of л-band properties with the field parallel to (H‖) or perpendicular to (H┴ ) the c-axis are investigated in detail. When a magnetic field is applied, either parallel or perpendicular to the c-axis, the density of the quasiparticle state (DOS) of the л-band proliferates quickly with increasing field, while the gap amplitude of the л-band decreases slowly, which is different from the recent theoretical calculations, showing a field dependent competition between the interband scattering and the pair-breaking effects.

  6. Enlargement of Photonic Band Gaps and Physical Picture of Photonic Band Structures

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yan; SHI Jun-Jie

    2006-01-01

    @@ Light propagation in a one-dimensional photonic crystal (PC), consisting of alternative slabs with refractive indices (layer thicknesses) n1 (a) and n2 (b), is investigated. An important optimal parameter matching condition,n1a ≈ n2b, is obtained for the largest photonic band gap (PBG). Moreover, we find that the exact analytical solutions for the electric/magnetic field eigenmodes at the band edges are standing waves with odd or even symmetry about the centre of each layer. The electric/magnetic field eigenfunctions at the top and bottom of the nth band have n and n - 1 nodes in one period of PC, respectively. The PBG arises from the symmetric differences of the field eigenfunctions at the band edges.

  7. Effects of extrinsic and intrinsic perturbations on the electronic structure of graphene: Retaining an effective primitive cell band structure by band unfolding

    Science.gov (United States)

    Medeiros, Paulo V. C.; Stafström, Sven; Björk, Jonas

    2014-01-01

    We use a band unfolding technique to recover an effective primitive cell picture of the band structure of graphene under the influence of different types of perturbations. This involves intrinsic perturbations, such as structural defects, and external ones, comprising nitrogen substitutions and the inclusion of graphene in adsorbed systems. In such cases, the band unfolding provides a reliable and efficient tool for quantitatively analyzing the effect of doping and defects on the electronic structure of graphene. We envision that this approach will become a standard method in the computational analysis of graphene's electronic structure in related systems.

  8. High-pressure crystal structures and superconductivity of Stannane (SnH4).

    Science.gov (United States)

    Gao, Guoying; Oganov, Artem R; Li, Peifang; Li, Zhenwei; Wang, Hui; Cui, Tian; Ma, Yanming; Bergara, Aitor; Lyakhov, Andriy O; Iitaka, Toshiaki; Zou, Guangtian

    2010-01-26

    There is great interest in the exploration of hydrogen-rich compounds upon strong compression where they can become superconductors. Stannane (SnH(4)) has been proposed to be a potential high-temperature superconductor under pressure, but its high-pressure crystal structures, fundamental for the understanding of superconductivity, remain unsolved. Using an ab initio evolutionary algorithm for crystal structure prediction, we propose the existence of two unique high-pressure metallic phases having space groups Ama2 and P6(3)/mmc, which both contain hexagonal layers of Sn atoms and semimolecular (perhydride) H(2) units. Enthalpy calculations reveal that the Ama2 and P6(3)/mmc structures are stable at 96-180 GPa and above 180 GPa, respectively, while below 96 GPa SnH(4) is unstable with respect to elemental decomposition. The application of the Allen-Dynes modified McMillan equation reveals high superconducting temperatures of 15-22 K for the Ama2 phase at 120 GPa and 52-62 K for the P6(3)/mmc phase at 200 GPa.

  9. Structural mechanisms of formation of adiabatic shear bands

    Directory of Open Access Journals (Sweden)

    Mikhail Sokovikov

    2016-10-01

    Full Text Available The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the

  10. Pattern reconfigurable antenna using electromagnetic band gap structure

    Science.gov (United States)

    Ismail, M. F.; Rahim, M. K. A.; Majid, H. A.; Hamid, M. R.; Yusoff, M. F. M.; Dewan, R.

    2017-01-01

    In this paper, a single rectangular patch antenna incorporated with an array of electromagnetic band gap (EBG) structures is proposed. The proposed antenna features radiation pattern agility by means of connecting the shorting pin vias to the EBG unit cells. The proposed design consists of 32 mm × 35.5 mm rectangular patch antenna and 10.4-mm-square mushroom-like EBG unit cells. The EBGs are placed at both sides of the antenna radiating patch and located on the thicker substrate of thickness, h. The copper tape which represents the PIN diode is used to control the connection between the EBG's via and the ground plane as reconfigurable mechanism of the antenna. The simulated result shows by switching the ON and OFF EBG structures in either sides or both, the directional radiation pattern can be tilted from 0 to +14°. The proposed antenna exhibits 7.2 dB realized gain at 2.42 GHz. The parametric study on EBG and antenna is also discussed.

  11. Projected shell model study of band structure of 90Nb

    Science.gov (United States)

    Kumar, Amit; Singh, Dhanvir; Gupta, Anuradha; Singh, Suram; Bharti, Arun

    2016-05-01

    A systematic study of two-quasiparticle bands of the odd-odd 90Nb nucleus is performed using the projected shell model approach. Yrast band with some other bands have been obtained and back-bending in moment of inertia has also been calculated and compared with the available experimental. On comparing the available experimental data, it is found that the treatment with PSM provides a satisfactory explanation of the available data.

  12. A Novel Idea for Coil Collar Structures in Accelerator Superconducting Magnets

    CERN Document Server

    Fessia, P

    2002-01-01

    The dipoles for several different machines (LHC, SSC, HERA) were designed using non-magnetic metallic collars to contain the superconducting coils. The coils are of two types, main and floating. This paper describes a structure with combined steel and plastic collars. Since the floating collars do not give an important contribution to the global rigidity of the dipole we propose to suppress them. The plastic collars are just fillers to limit the helium contained in the cold mass. Some data about thermoplastic materials to be possibly used for the collars are given and some estimations of mass and cost of this configuration are made. Finally the results of the tests of a 1-m-long twin aperture dipole with mixed steel-plastic collars are shortly described. The replacement of expensive alloys by high performance plastic in non-structural components can be a cost-effective solution in view of future projects where superconducting magnets are involved and contained costs are a key issue.

  13. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure.

    Science.gov (United States)

    Gruznev, D V; Bondarenko, L V; Tupchaya, A Y; Eremeev, S V; Mihalyuk, A N; Chou, J P; Wei, C M; Zotov, A V; Saranin, A A

    2017-01-25

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), [Formula: see text]-(Tl, Pb) and [Formula: see text]-(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)[Formula: see text] system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound contains six Tl atoms and seven Pb atoms per [Formula: see text] unit cell (i.e.  ∼0.67 ML Tl and  ∼0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] and (Tl, Pb)/Ge(1 1 1)[Formula: see text] compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)[Formula: see text], these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  14. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure

    Science.gov (United States)

    Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Eremeev, S. V.; Mihalyuk, A. N.; Chou, J. P.; Wei, C. M.; Zotov, A. V.; Saranin, A. A.

    2017-01-01

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), \\sqrt{3}× \\sqrt{3} -(Tl, Pb) and 3× 3 -(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)3× 3 compound contains six Tl atoms and seven Pb atoms per 3× 3 unit cell (i.e.  ˜0.67 ML Tl and  ˜0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} and (Tl, Pb)/Ge(1 1 1)3× 3 compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} , these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  15. Scaling between superconducting critical temperature and structural coherence length in YBa2Cu3O6.9 films

    Science.gov (United States)

    Gauzzi, A.; Jönsson-Åkerman, B. Johan; Clerc-Dubois, A.; Pavuna, D.

    2000-09-01

    Measurements of critical temperature Tc in superconducting YBa2Cu3O6.9 films with reduced long-range structural order show the validity of the empirical scaling relation ΔTc propto rc-2 between disorder-induced reduction of Tc and structural coherence length rc in the ab-plane. This result is quantitatively explained by the disorder-induced confinement of the charge carriers within each ordered domain of size rc. Our analysis of the data based on this picture enables us to precisely determine the Ginzburg-Landau superconducting coherence length in the ab-plane, ξab = 1.41 ± 0.04 nm.

  16. The New Superconductor tP-SrPd2Bi2: Structural Polymorphism and Superconductivity in Intermetallics.

    Science.gov (United States)

    Xie, Weiwei; Seibel, Elizabeth M; Cava, Robert J

    2016-04-01

    We consider a system where structural polymorphism suggests the possible existence of superconductivity through the implied structural instability. SrPd2Bi2 has two polymorphs, which can be controlled by the synthesis temperature: a tetragonal form (CaBe2Ge2-type) and a monoclinic form (BaAu2Sb2-type). Although the crystallographic difference between the two forms may, at first, seem trivial, we show that tetragonal SrPd2Bi2 is superconducting at 2.0 K, whereas monoclinic SrPd2Bi2 is not. We rationalize this finding and place it in context with other 1-2-2 phases.

  17. A unified perspective of complex band structure: interpretations, formulations, and applications

    Science.gov (United States)

    Reuter, Matthew G.

    2017-02-01

    Complex band structure generalizes conventional band structure by also considering wavevectors with complex components. In this way, complex band structure describes both the bulk-propagating states from conventional band structure and the evanescent states that grow or decay from one unit cell to the next. Even though these latter states are excluded by translational symmetry, they become important when translational symmetry is broken via, for example, a surface or impurity. Many studies over the last 80 years have directly or indirectly developed complex band structure for an impressive range of applications, but very few discuss its fundamentals or compare its various results. In this work we build upon these previous efforts to expose the physical foundation of complex band structure, which mathematically implies its existence. We find that a material’s static and dynamic electronic structure are both completely described by complex band structure. Furthermore, we show that complex band structure reflects the minimal, intrinsic information contained in the material’s Hamiltonian. These realizations then provide a context for comparing and unifying the different formulations and applications of complex band structure that have been reported over the years. Ultimately, this discussion introduces the idea of examining the amount of information contained in a material’s Hamiltonian so that we can find and exploit the minimal information necessary for understanding a material’s properties.

  18. Superconducting microfabricated ion traps

    CERN Document Server

    Wang, Shannon X; Labaziewicz, Jaroslaw; Dauler, Eric; Berggren, Karl; Chuang, Isaac L

    2010-01-01

    We fabricate superconducting ion traps with niobium and niobium nitride and trap single 88Sr ions at cryogenic temperatures. The superconducting transition is verified and characterized by measuring the resistance and critical current using a 4-wire measurement on the trap structure, and observing change in the rf reflection. The lowest observed heating rate is 2.1(3) quanta/sec at 800 kHz at 6 K and shows no significant change across the superconducting transition, suggesting that anomalous heating is primarily caused by noise sources on the surface. This demonstration of superconducting ion traps opens up possibilities for integrating trapped ions and molecular ions with superconducting devices.

  19. Band Structure and Fermi-Surface Properties of Ordered beta-Brass

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt; Christensen, N. E.

    1973-01-01

    The band structure of ordered β-brass (β′-CuZn) has been calculated throughout the Brillouin zone by the augmented-plane-wave method. The present band model differs from previous calculations with respect to the position and width of the Cu 3d band. The derived dielectric function ε2(ω) and the p...

  20. True photonic band-gap mode-control in VCSEL structures

    DEFF Research Database (Denmark)

    Romstad, F.; Madsen, M.; Birkedal, Dan;

    2003-01-01

    Photonic band-gap mode confinement in novel nano-structured large area VCSEL structures is confirmed by the amplified spontaneous emission spectrum. Both guide and anti-guide VCSEL structures are experimentally characterised to verify the photonic band-gap effect....

  1. Orbital-Parity Selective Superconducting Pairing Structures of Fe-based Superconductors under Glide Symmetry

    Science.gov (United States)

    Lin, Chiahui; Chou, Chung-Pin; Yin, Wei-Guo; Ku, Wei

    2014-03-01

    We show that the superconductivity in Fe-based superconductors consists of zero and finite momentum (π , π , 0) Cooper pairs with the same and different parities of the Fe 3 d orbitals respectively. The former develops the distinct gap structures for each orbital parity, and the latter is characteristic of spin singlet, spacial oddness and time reversal symmetry breaking. This originates from the unit cell containing two Fe atoms and two anions of staggered positioning with respect to the Fe square lattice. The in-plane translation is turned into glide translation, which dictates orbital-parity selective quasiparticles. Such novel pairing structures explain the unusual gap angular modulation on the hole pockets in recent ARPES and STS experiments. Work supported by DOE DE-AC02-98CH10886 and Chinese Academy of Engineering Physics and Ministry of Science and Technology.

  2. Structural, elastic and electronic properties of superconducting anti-perovskites MgCNi 3, ZnCNi 3 and CdCNi 3 from first principles

    Science.gov (United States)

    Shein, I. R.; Bannikov, V. V.; Ivanovskii, A. L.

    2008-01-01

    First principle total energy calculations using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential were performed to investigate the systematic trends for structural, elastic and electronic properties of the family of superconducting anti-perovskites MCNi 3 depending from the type of M cations (M are Mg, Zn and Cd). In result the optimized lattice parameters, independent elastic constants ( C11, C12 and C44), bulk modulus B, compressibility β, shear modulus G and tetragonal shear modulus G‧ are evaluated. Further, for the first time the numerical estimates of a set of elastic parameters (bulk and shear modulus, Young’s modulus Y, Poisson’s ratio ( ν), Lamé’s coefficients ( μ, λ)) of the polycrystalline superconducting MCNi 3 ceramics (in framework of the Voigt-Reuss-Hill approximation) were performed. Besides, the band structures, densities of states (DOS), total and site-projected l-decomposed DOS at the Fermi level, the shapes of the Fermi surfaces, the Sommerfeld’s coefficients and the molar Pauli paramagnetic susceptibility for these anti-perovskites were obtained and analyzed in comparison with the available theoretical and experimental data.

  3. Self-consistent treatment of v-groove quantum wire band structure in no parabolic approximation

    Directory of Open Access Journals (Sweden)

    Crnjanski Jasna V.

    2004-01-01

    Full Text Available The self-consistent no parabolic calculation of a V-groove-quantum-wire (VQWR band structure is presented. A comparison with the parabolic flat-band model of VQWR shows that both, the self-consistency and the nonparabolicity shift sub band edges, in some cases even in the opposite directions. These shifts indicate that for an accurate description of inter sub band absorption, both effects have to be taken into the account.

  4. Simultaneous suppression of superconductivity and structural phase transition under pressure in Ca10(Ir4As8)(Fe2 -xIrxAs2)5

    Science.gov (United States)

    Kitagawa, Shunsaku; Araki, Shingo; Kobayashi, Tatsuo C.; Ishii, Hiroyuki; Fujimura, Kazunori; Mitsuoka, Daisuke; Kudo, Kazutaka; Nohara, Minoru

    2014-12-01

    We measured the pressure dependence of in-plane resistivity ρa b in the recently discovered iron-based superconductor Ca10(Ir4As8) (Fe2-xIrxAs2) 5 , which shows a unique structural phase transition in the absence of magnetic ordering, with a superconducting transition temperature Tc=16 K and a structural phase transition temperature Ts≃100 K at ambient pressure. Tc and Ts are suppressed on applying pressure and disappear at approximately 0.5 GPa, suggesting a relationship between superconductivity and structure. Ca10(Ir4As8) (Fe2-xIrxAs2) 5 is a rather rare example in which the superconductivity appears only in a low-temperature ordered phase. The fact that the change in the crystal structure is directly linked with superconductivity suggests that the crystal structure as well as magnetism are important factors governing superconductivity in iron pnictides.

  5. First Principles Study of Band Structure and Band Gap Engineering in Graphene for Device Applications

    Science.gov (United States)

    2015-03-20

    successfully to realise the full applications of graphene? What is the current status of the graphene based devices or Electronics ? How the graphene...gap value has increased to 1.5eV. It is reflected in the density of states (Fig.20c). The nitrogen atoms are at a distance of 5Ȧ. And there is a...completely modified.The calculation of surface doping of graphene with S is repeated with 96 atom simulation cell. The band gap value is 0.7 eV. The value of

  6. Photonic band gap of one-dimensional periodic structure containing dispersive left-handed metamaterials

    Institute of Scientific and Technical Information of China (English)

    Zhanshan Wang; Tian Sang; Fengli Wang; Yonggang Wu; Lingyan Chen

    2008-01-01

    Band structures of one-dimensional(1D)photonic crystals(PCs)containing dispersive left-handed metamaterials are studied theoretically.The results show that the structure possesses a type of photonic band gap originating from total internal reflection(TIR).In contrast to photonic band gaps corresponding to zero average refractive index and zero phase.the TIR gap exhibits sharp angular effect and has no polarization effect.It should also be noted that band structures of transverse electric(TE) and transverse magnetic(TM) mode waves are exactly the same in the PCs we studied.

  7. Theoretical study on the band structure and optical properties of 4H-SiC

    Institute of Scientific and Technical Information of China (English)

    Xu Peng-Shou; Xie Chang-Kun; Pan Hai-Bin; Xu Fa-Qiang

    2004-01-01

    We have studied the band structure and optical properties of 4H-SiC by using a full potential linearized augmented plane waves (FPLAPW) method. The density of states (DOS) and band structure are presented. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With band gap correction, the real part of the dielectric function has been derived from the imaginary part by the Kramers-Kronig (KK) dispersion relationship. The values of reflectivity for normal incidence as a function of photon energy have also been calculated.We found the theoretical results are in good agreement with the experimental data.

  8. Design and analysis of defected ground structure transformer for dual-band antenna

    Directory of Open Access Journals (Sweden)

    Wai-Wa Choi

    2014-12-01

    Full Text Available This study presents a novel dual-band antenna design methodology utilising a dual-frequency impedance transformer with defected ground structure (DGS. The proposed dual-frequency DGS impedance transformer generates a second resonant frequency from a conventional single-band antenna, resulting dual-band operation. Simulation studies illustrate that the adopted design achieves versatile configurations for arbitrary operating frequencies and diverse input impedance ranges in planar antenna structures. To experimentally verify the proposed design methodology, a dual-frequency DGS impedance transformer was implemented for a 2.4 GHz monopole antenna to obtain a 900/2400 MHz dual-band antenna. Measurement shows that the 10 dB return loss bandwidth in 900 MHz band is 34.4 MHz, whereas that in 2400 MHz band is wider than 530 MHz. Typical monopole radiation patterns are observed at both operating bands.

  9. Structure of dipole bands in doubly odd 102Ag

    Science.gov (United States)

    Singh, V.; Sihotra, S.; Malik, S. S.; Bhat, G. H.; Palit, R.; Sheikh, J. A.; Kumar, S.; Singh, N.; Singh, K.; Goswamy, J.; Sethi, J.; Saha, S.; Trivedi, T.; Mehta, D.

    2016-10-01

    Excited states in the transitional doubly odd 102Ag nucleus were populated in the 75As(31P,p 3 n ) fusion-evaporation reaction using the 125 MeV incident 31P beam. The subsequent deexcitations were investigated through in-beam γ -ray spectroscopic techniques using the Indian National Gamma Array spectrometer equipped with 21 clover Ge detectors. The level scheme in 102Ag has been established up to excitation energy ˜6.5 MeV and angular momentum 19 ℏ . The earlier reported level scheme is considerably extended and modified to result in a pair of nearly degenerate negative-parity dipole bands. Lifetime measurements for the states of these two dipole bands have been performed by using the Doppler-shift attenuation method. The two nearly degenerate bands exhibit different features with regard to kinetic moment of inertia, and the reduced transition probabilities B (M 1 ) and B (E 2 ) , which do not favor these to be chiral partners. These bands are discussed in the framework of the hybrid version of tilted-axis cranking (tac) model calculations and assigned the π g9 /2⊗ν h11 /2 and π g9 /2⊗ν h11 /2(d5/2/g7 /2) 2 configurations. The tac model calculations are extended to the nearly degenerate bands observed in the heavier doubly odd Ag-108104 isotopes.

  10. Electronic structure, magnetic and superconducting properties of co-doped iron-arsenide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Rosner, Helge; Schnelle, Walter; Nicklas, Michael; Leithe-Jasper, Andreas [MPI CPfS Dresden (Germany); Weikert, Franziska [Los Alamos National Laboratory, New Mexico (United States); HLD Dresden Rossendorf (Germany); Wosnitza, Joachim [HLD Dresden Rossendorf (Germany)

    2013-07-01

    We present a joint experimental and theoretical study of co-doped iron-arsenide superconductors of the 122 family A{sub 1-x}K{sub x}Fe{sub 2-y}T{sub y}As{sub 2} (A = Ba,Sr,Eu; T = Co,Ru,Rh). In these systems, the co-doping enables the separation of different parameters - like electron count, disorder or the specific geometry of the FeAs layer - with respect to the position of the respective compounds in the general 122 phase diagram. For a series of compounds, we investigate the relevance of the different parameters for the magnetic, thermodynamic and superconducting properties. Our experimental investigations are supported by density functional electronic structure calculations applying different approximations for doping and disorder.

  11. Superconductivity on the density-wave background with soliton-wall structure

    Science.gov (United States)

    Grigoriev, P. D.

    2009-03-01

    Superconductivity (SC) may microscopically coexist with density wave (DW) when the nesting of the Fermi surface (FS) is not perfect. There are, at least, two possible microscopic structures of a DW state with quasi-particle states remaining on the Fermi level and leading to the Cooper instability: (i) the soliton-wall phase and (ii) the small ungapped FS pockets. The dispersion of such quasi-particle states strongly differs from that without DW, and so do the properties of SC on the DW background. The upper critical field H in such an SC state strongly increases as the system approaches the critical pressure, where SC first appears. H may considerably exceed its typical value without DW and has unusual upward curvature as function of temperature. The results obtained explain the experimental observations in layered organic superconductors (TMTSF)2PF6 and α-(BEDT-TTF)2KHg(SCN)4.

  12. Study on the electronic structures of REBaCuO superconductors and their relation to superconductivity

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Electronic structures of REBaCuO(RE=La, Pr, Nd, Sm, Gd, Dy, Ho and Er)systems were calculated by means of SCF-Xα -SW methods. Results show that there is an inner-orbit coupling for these oxide superconductor systems. The inner-orbit coupling was resulted from the interaction of two electronic orbits of RE 5p and O 2s, since they have similar energy state levels and relatively larger orbital electronic clouds. Compared with experimental facts, it is also found that the overlap in space between the two orbits has a similar tendency to Tc and the number of enrolling electrons has a close relation to Jc, therefore, the influence of inner-orbit coupling on superconductivity could not be overlooked.

  13. Probing atomic structure and Majorana wavefunctions in mono-atomic Fe chains on superconducting Pb surface

    Science.gov (United States)

    Pawlak, Rémy; Kisiel, Marcin; Klinovaja, Jelena; Meier, Tobias; Kawai, Shigeki; Glatzel, Thilo; Loss, Daniel; Meyer, Ernst

    2016-11-01

    Motivated by the striking promise of quantum computation, Majorana bound states (MBSs) in solid-state systems have attracted wide attention in recent years. In particular, the wavefunction localisation of MBSs is a key feature and is crucial for their future implementation as qubits. Here we investigate the spatial and electronic characteristics of topological superconducting chains of iron atoms on the surface of Pb(110) by combining scanning tunnelling microscopy and atomic force microscopy. We demonstrate that the Fe chains are mono-atomic, structured in a linear manner and exhibit zero-bias conductance peaks at their ends, which we interpret as signature for a MBS. Spatially resolved conductance maps of the atomic chains reveal that the MBSs are well localised at the chain ends (≲25 nm), with two localisation lengths as predicted by theory. Our observation lends strong support to use MBSs in Fe chains as qubits for quantum-computing devices.

  14. Investigation of structure of superconducting power transmission cables with LN2 counter-flow cooling

    Science.gov (United States)

    Furuse, Mitsuho; Fuchino, Shuichiro; Higuchi, Noboru

    2003-04-01

    Establishment of long-distance cooling techniques and design of a compact cross section are required for development of HTC superconducting underground power cables. To save space of return coolant, a counter-flow cooling system appears promising. However, it is difficult to cool down long cables because of heat exchange between counter-flows due to high thermal conductivity of dielectric materials which separate both flows in range of liquid nitrogen temperature. We estimated temperature distributions analytically along model HTS power cables with counter-flow. Results of calculation showed that when liquid-nitrogen-impregnated polypropylene laminated paper was chosen for a dielectric material, great thickness was required to reduce heat exchange between counter-flows. We investigated various cable structures to optimize the counter-flow cooling system and cable size.

  15. An improved phase-control system for superconducting low-velocity accelerating structures

    Energy Technology Data Exchange (ETDEWEB)

    Bogaty, J.M.; Clifft, B.E.; Shepard, K.W.; Zinkann, G.P.

    1989-01-01

    Microphonic fluctuations in the rf eigenfrequency of superconducting (SC) slow-wave structures must be compensated by a fast-tuning system in order to control the rf phase. The tuning system must handle a reactive power proportional to the product of the tuning range and the rf energy content of the resonant cavity. The accelerating field level of many of the SC cavities forming the ATLAS linac has been limited by the rf power capacity of the presently used PIN-diode based fast-tuner. A new system has been developed, utilizing PIN diodes operating immersed in liquid nitrogen, with the diodes controlled by a high-voltage VMOS FET driver. The system has operated at reactive power levels above 20 KVA, a factor of four increase over an earlier design. 7 refs., 2 figs.

  16. Band structures in silicene on monolayer gallium phosphide substrate

    Science.gov (United States)

    Ren, Miaojuan; Li, Mingming; Zhang, Changwen; Yuan, Min; Li, Ping; Li, Feng; Ji, Weixiao; Chen, Xinlian

    2016-07-01

    Opening a sizable band gap in the zero-gap silicene is a key issue for its application in nanoelectronics. We design new 2D silicene and GaP heterobilayer (Si/GaP HBL) composed of silicene and monolayer (ML) GaP. Based on first-principles calculations, we find that the interaction energies are in the range of -295.5 to -297.5 meV per unit cell, indicating a weak interaction between silicene and gallium phosphide (GaP) monolayer. The band gap changes ranging from 0.06 to 0.44 eV in hybrid HBLs. An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern. These provide a possible way to design effective FETs out of silicene on GaP monolayer.

  17. The spin polarized band structure of strained thin films of gadolinium

    Energy Technology Data Exchange (ETDEWEB)

    Waldfried, C.; Dowben, P.A. [Univ. of Nebraska, Lincoln, NE (United States); Vescovo, E. [Brookhaven National Lab., Upton, NY (United States). National Synchrotron Light Source

    1998-12-31

    The magnetic properties of strained thin films of gadolinium are characterized by a wave vector and thickness dependence of the exchange splitting. The spin-resolved band structure has been mapped by spin polarized photoemission, and provides considerable insight into the relationship between magnetism of local moment systems, and band structure.

  18. Volume and surface photoemission from tungsten. I. Calculation of band structure and emission spectra

    DEFF Research Database (Denmark)

    Christensen, N. Egede; Feuerbacher, B.

    1974-01-01

    The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure...

  19. Comparative studies in method for stratigraphical structure measurement of ice cores: Identification of cloudy bands

    Institute of Scientific and Technical Information of China (English)

    Morimasa Takata; Hitoshi Shoji; Atsushi Miyamoto; Kimiko Shimohara

    2003-01-01

    Cloudy bands are typical stratigraphic structure in deep ice core.Detailed recording of cloudy bands is important for dating of ice core since pair of series cloudy band and clear layer is corresponds to annual layer and it sometimes corresponds to volcanic ash layer.We developed two type scanners, transmitted light method and laser tomograph method for the stratigraphic study.Measurements were carried out for NGRIP deep ice core, which containing many cloudy bands, using the two type scanners and digital camera.We discussed about the possibility of identification of cloudy bands by each method and about advantage and disadvantage of measurements and their results.

  20. Band structures of TiO2 doped with N, C and B*

    OpenAIRE

    2006-01-01

    This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the...

  1. Superconductivity versus bound-state formation in a two-band superconductor with small Fermi energy: Applications to Fe pnictides/chalcogenides and doped SrTiO3

    Science.gov (United States)

    Chubukov, Andrey V.; Eremin, Ilya; Efremov, Dmitri V.

    2016-05-01

    We analyze the interplay between superconductivity and the formation of bound pairs of fermions (BCS-BEC crossover) in a 2D model of interacting fermions with small Fermi energy EF and weak attractive interaction, which extends to energies well above EF. The 2D case is special because a two-particle bound state forms at arbitrary weak interaction, and already at weak coupling, one has to distinguish between the bound-state formation and superconductivity. We briefly review the situation in the one-band model and then consider two different two-band models: one with one hole band and one electron band and another with two hole or two electron bands. In each case, we obtain the bound-state energy 2 E0 for two fermions in a vacuum and solve the set of coupled equations for the pairing gaps and the chemical potentials to obtain the onset temperature of the pairing Tins and the quasiparticle dispersion at T =0 . We then compute the superfluid stiffness ρs(T =0 ) and obtain the actual Tc. For definiteness, we set EF in one band to be near zero and consider different ratios of E0 and EF in the other band. We show that at EF≫E0 , the behavior of both two-band models is BCS-like in the sense that Tc≈Tins≪EF and Δ ˜Tc . At EF≪E0 , the two models behave differently: in the model with two hole/two electron bands, Tins˜E0/lnE/0EF , Δ ˜(E0EF) 1 /2 , and Tc˜EF , like in the one-band model. In between Tins and Tc, the system displays a preformed pair behavior. In the model with one hole and one electron bands, Tc remains of order Tins, and both remain finite at EF=0 and of the order of E0. The preformed pair behavior still does exist in this model because Tc is numerically smaller than Tins. For both models, we reexpress Tins in terms of the fully renormalized two-particle scattering amplitude by extending to the two-band case (the method pioneered by Gorkov and Melik-Barkhudarov back in 1961). We apply our results for the model with a hole and an electron band to

  2. Effect of acicular ferrite on banded structures in low-carbon microalloyed steel

    Institute of Scientific and Technical Information of China (English)

    Lei Shi; Ze-sheng Yan; Yong-chang Liu; Xu Yang; Cheng Zhang; Hui-jun Li

    2014-01-01

    The effect of acicular ferrite (AF) on banded structures in low-carbon microalloyed steel with Mn segregation during both iso-thermal transformation and continuous cooling processes was studied by dilatometry and microscopic observation. With respect to the iso-thermal transformation process, the specimen isothermed at 550°C consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450°C exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50°C/s, a mixture of AF and martensite formed in both segregated bands, and the volume fraction of martensite in Mn-rich bands was always higher than that in Mn-poor bands. An increased cooling rate resulted in a decrease in the difference of martensite volume fraction between Mn-rich and Mn-poor bands and thereby leaded to less distinct microstructural banding. The results show that Mn segregation and cooling rate strongly affect the formation of AF-containing banded structures. The formation mechanism of microstructural banding was also discussed.

  3. Study on relationships of electromagnetic band structures and left/right handed structures

    Institute of Scientific and Technical Information of China (English)

    GAO Chu; CHEN ZhiNing; WANG YunYi; YANG Ning

    2007-01-01

    Two types of dual periodic circuits are introduced. The distributions of passbands and stopbands are generated from their dispersion relationships. Based on the study, Brillouin diagrams of three representative special cases are drawn; S parameters of these three cases are simulated by Aglient ADS; the S parameters of one of the three cases are verified by an experiment. The phase characteristics are compared with those generated from the dispersion relationship. The theoretical analysis and the experimental verification show that both types of the periodic structures can behave as electromagnetic band gap (EBG) structures, right-handed structures (RHS), and left-handed structures (LHS), when they operate at different frequency ranges. Thus, the possibility of a physical structure showing these three different characteristics at different frequency ranges is proven.

  4. Band Structure and Optical Properties of Ordered AuCu3

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt; Lengkeek, H. P.

    1979-01-01

    The optical spectra of ordered AuCu3 have been measured at low temperatures by a direct ellipsometric technique. We find several structural elements above the absorption edge as well as in the infrared. The measured spectra are interpreted in terms of the interband absorption calculated from an ab...... initio band structure obtained by the relativistic linear muffin-tin orbitals method. The band calculation reveals that ordered AuCu3 has distinct copper and gold d bands positioned in and hybridizing with an s band common to copper and gold. The calculated state density is found to be in good agreement...

  5. Structural and superconducting properties of ion beam sputtered Nb thin films and Nb/Cu bilayers

    Science.gov (United States)

    Nath, S. K.; Dhawan, R.; Rai, S.; Lodha, G. S.; Sokhey, K. J. S.

    2012-01-01

    We present the results of a study of structural and superconducting properties of polycrystalline Nb thin films (200 Å, 300 Å, 400 Å, 700 Å and 1000 Å) and Nb/Cu bilayers (300 Å/300 Å and 400 Å/300 Å) prepared on Si substrates by ion beam sputtering at room temperature. The thicknesses, roughnesses at the surfaces and interfaces were determined by X-ray reflectivity whereas the grain sizes were determined from grazing incidence X-ray diffraction and transmission electron microscopic studies. The superconducting transition temperature ( T C) of Nb thin films are smaller than T C of bulk Nb. The Nb-200 Å sample does not show T C down to 2.3 K. The average size of the grains varies from 42 Å for Nb-200 Å sample to 69 Å for Nb-1000 Å sample. Our results show that the T C in these polycrystalline films is not only limited by its thickness but also by the size of the grains. The Nb films deposited in situ on the Cu layer (Nb/Cu) show a marginal increase in average sizes of the grains as compare to their respective values in Nb films of same thicknesses. As a result a marginal increase in T C of these films is also observed. The maximum decrease in T C due to oxygen intake during deposition should be about 0.5 K from its bulk value (9.28 K). We have attributed the large decrease in T C in our case on the basis of decrease in the Debye temperature and density of states at the Fermi level for Nb thin films as compared to their respective values for bulk Nb.

  6. Hybridized Abrikosov Flux-lines and Pancake Vortices in Two-band Superconductors with Mixed Dimensionality

    Science.gov (United States)

    Tanaka, K.; Eschrig, M.

    2008-03-01

    We study electronic structure and thermodynamic properties of a two-band superconductor, in which one band is ballistic and quasi-two dimensional (2D), and the other is diffusive and three dimensional (3D). We assume that superconductivity in the 3D diffusive band is ``weak'', i.e., mostly induced, as is the case in MgB2. Hybridization with the ``weak'' 3D diffusive band has significant and intriguing influence on the electronic properties of the ``strong'' 2D ballistic band. In particular, the effects of Coulomb interactions in the diffusive band and unusual Kramer-Pesch effect are examined. Furthermore, based on a circular-cell approximation within the quasiclassical theory of superconductivity, we explore the effects of magnetic field on vortex structure in such a two-band superconductor. We discuss hybridization of Abrikosov flux lines in the 3D diffusive band with pancake vortices in the 2D ballistic band.

  7. Applied superconductivity

    CERN Document Server

    Newhouse, Vernon L

    1975-01-01

    Applied Superconductivity, Volume II, is part of a two-volume series on applied superconductivity. The first volume dealt with electronic applications and radiation detection, and contains a chapter on liquid helium refrigeration. The present volume discusses magnets, electromechanical applications, accelerators, and microwave and rf devices. The book opens with a chapter on high-field superconducting magnets, covering applications and magnet design. Subsequent chapters discuss superconductive machinery such as superconductive bearings and motors; rf superconducting devices; and future prospec

  8. Band structures of TiO2 doped with N, C and B

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result.Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

  9. High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4.

    Science.gov (United States)

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Gomis, Oscar; Achary, S Nagabhusan; Popescu, Catalin; Patwe, Sadeque J; Tyagi, Avesh K

    2016-05-16

    The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations.

  10. Band structure of germanium carbides for direct bandgap silicon photonics

    Science.gov (United States)

    Stephenson, C. A.; O'Brien, W. A.; Penninger, M. W.; Schneider, W. F.; Gillett-Kunnath, M.; Zajicek, J.; Yu, K. M.; Kudrawiec, R.; Stillwell, R. A.; Wistey, M. A.

    2016-08-01

    Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge1-xCx (x = 0.78%) using density functional theory with HSE06 hybrid functionals predicts a splitting of the conduction band at Γ and a strongly direct bandgap, consistent with band anticrossing. Photoreflectance of Ge0.998C0.002 shows a bandgap reduction supporting these results. Growth of Ge0.998C0.002 using tetrakis(germyl)methane as the C source shows no signs of C-C bonds, C clusters, or extended defects, suggesting highly substitutional incorporation of C. Optical gain and modulation are predicted to rival III-V materials due to a larger electron population in the direct valley, reduced intervalley scattering, suppressed Auger recombination, and increased overlap integral for a stronger fundamental optical transition.

  11. Ultra-broad band and dual-band highly efficient polarization conversion based on the three-layered chiral structure

    Science.gov (United States)

    Xu, Kai-kai; Xiao, Zhong-yin; Tang, Jing-yao; Liu, De-jun; Wang, Zi-hua

    2016-07-01

    In the paper, a novel three-layered chiral structure is proposed and investigated, which consists of a split-ring resonator sandwiched between two layers of sub-wavelength gratings. This designed structure can achieve simultaneously asymmetric transmission with an extremely broad bandwidth and high amplitude as well as multi-band 90° polarization rotator with very low dispersion. Numerical simulations adopted two kinds of softwares with different algorithms demonstrate that asymmetric parameter can reach a maximum of 0.99 and over than 0.8 from 4.6 to 16.8 GHz, which exhibit magnitude and bandwidth improvement over previous chiral metamaterials in microwave bands (S, C, X and Ku bands). Specifically, the reason of high amplitude is analyzed in detail based on the Fabry-perot like resonance. Subsequently, the highly efficient polarization conversion with very low dispersion between two orthogonal linearly polarized waves is also analyzed by the optical activity and ellipticity. Finally, the electric fields are also investigated and further demonstrate the correctness of the simulated and calculated results.

  12. Energy band structure tailoring of vertically aligned InAs/GaAsSb quantum dot structure for intermediate-band solar cell application by thermal annealing process.

    Science.gov (United States)

    Liu, Wei-Sheng; Chu, Ting-Fu; Huang, Tien-Hao

    2014-12-15

    This study presents an band-alignment tailoring of a vertically aligned InAs/GaAs(Sb) quantum dot (QD) structure and the extension of the carrier lifetime therein by rapid thermal annealing (RTA). Arrhenius analysis indicates a larger activation energy and thermal stability that results from the suppression of In-Ga intermixing and preservation of the QD heterostructure in an annealed vertically aligned InAs/GaAsSb QD structure. Power-dependent and time-resolved photoluminescence were utilized to demonstrate the extended carrier lifetime from 4.7 to 9.4 ns and elucidate the mechanisms of the antimony aggregation resulting in a band-alignment tailoring from straddling to staggered gap after the RTA process. The significant extension in the carrier lifetime of the columnar InAs/GaAsSb dot structure make the great potential in improving QD intermediate-band solar cell application.

  13. Chaos and band structure in a three-dimensional optical lattice.

    Science.gov (United States)

    Boretz, Yingyue; Reichl, L E

    2015-04-01

    Classical chaos is known to affect wave propagation because it signifies the presence of broken symmetries. The effect of chaos has been observed experimentally for matter waves, electromagnetic waves, and acoustic waves. When these three types of waves propagate through a spatially periodic medium, the allowed propagation energies form bands. For energies in the band gaps, no wave propagation is possible. We show that optical lattices provide a well-defined system that allows a study of the effect of chaos on band structure. We have determined the band structure of a body-centered-cubic optical lattice for all theoretically possible couplings, and we find that the band structure for those lattices realizable in the laboratory differs significantly from that expected for the bands in an "empty" body-centered-cubic crystal. However, as coupling is increased, the lattice becomes increasingly chaotic and it becomes possible to produce band structure that has behavior qualitatively similar to the "empty" body-centered-cubic band structure, although with fewer degeneracies.

  14. Tuning the band gap in hybrid tin iodide perovskite semiconductors using structural templating.

    Science.gov (United States)

    Knutson, Jeremy L; Martin, James D; Mitzi, David B

    2005-06-27

    Structural distortions within the extensive family of organic/inorganic hybrid tin iodide perovskite semiconductors are correlated with their experimental exciton energies and calculated band gaps. The extent of the in- and out-of-plane angular distortion of the SnI4(2-) perovskite sheets is largely determined by the relative charge density and steric requirements of the organic cations. Variation of the in-plane Sn-I-Sn bond angle was demonstrated to have the greatest impact on the tuning of the band gap, and the equatorial Sn-I bond distances have a significant secondary influence. Extended Hückel tight-binding band calculations are employed to decipher the crystal orbital origins of the structural effects that fine-tune the band structure. The calculations suggest that it may be possible to tune the band gap by as much as 1 eV using the templating influence of the organic cation.

  15. Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

    Energy Technology Data Exchange (ETDEWEB)

    Kozyukhin, S., E-mail: sergkoz@igic.ras.ru [Russian Academy of Science, Institute of General and Inorganic Chemistry (Russian Federation); Golovchak, R. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Kovalskiy, A. [Lehigh University, Department of Materials Science and Engineering (United States); Shpotyuk, O. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Jain, H. [Lehigh University, Department of Materials Science and Engineering (United States)

    2011-04-15

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

  16. Detailed Study of the TE band structure of two dimensional metallic photonic crystals with square symmetry

    Science.gov (United States)

    Sedghi, Aliasghar; Valiaghaie, Soma; Soufiani, Ahad Rounaghi

    2014-10-01

    By virtue of the efficiency of the Dirichlet-to-Neumann map method, we have calculated, for H-polarization (TE mode), the band structure of 2D photonic crystals with a square lattice composed of metallic rods embedded in an air background. The rod in the unit cell is chosen to be circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have studied the band structure as a function of the size of the rods. We have also studied the flat bands appearing in the band structures and have shown that for frequencies around the surface plasmon frequency, the modes are highly localized at the interface between the metallic rods and the air background.

  17. Obtaining the band structure of a complicated photonic crystal by linear operations

    Institute of Scientific and Technical Information of China (English)

    吴良; 叶卓; 何赛灵

    2003-01-01

    Absolute band gaps can be created by lifting the degeneracy in the bands of a photonic crystal.To calculate the band structure of a complicated photonic crystal generated by e.g.symmetry breaking,general forms of all possible linear operations are presented in terms of matrices and a procedure to combine these operations is given.Other forms of linear operations(such as the addition,subtraction,and translation transforms) are also presented to obtain an explicit expression for the Fourier coefficient of the dielectric function in the plane-wave expansion method.With the present method,band structures for various complicated photonic crystals(related through these linear operations) can be obtained easily and quickly.As a numerical example,a large absolute band gap for a complicated photonic crystal structure of GaAs is found in the high region of normalized frequency.

  18. Detailed study of the TE band structure of two dimensional metallic photonic crystals with square symmetry

    Energy Technology Data Exchange (ETDEWEB)

    Sedghi, Aliasghar [Islamic Azad University, Shabestar (Iran, Islamic Republic of); Valiaghaie, Soma [Islamic Azad University, Sanandaj (Iran, Islamic Republic of); Soufiani, Ahad Rounaghi [Islamic Azad University, Sufian (Iran, Islamic Republic of)

    2014-10-15

    By virtue of the efficiency of the Dirichlet-to-Neumann map method, we have calculated, for H-polarization (TE mode), the band structure of 2D photonic crystals with a square lattice composed of metallic rods embedded in an air background. The rod in the unit cell is chosen to be circular in shape. Here, from a practical point of view, in order to obtain maximum band gaps, we have studied the band structure as a function of the size of the rods. We have also studied the flat bands appearing in the band structures and have shown that for frequencies around the surface plasmon frequency, the modes are highly localized at the interface between the metallic rods and the air background.

  19. Photonic Band Gaps in Two-Dimensional Crystals with Fractal Structure

    Institute of Scientific and Technical Information of China (English)

    刘征; 徐建军; 林志方

    2003-01-01

    We simulate the changes of the photonic band structure of the crystal in two dimensions with a quasi-fractal structure when it is fined to a fractal. The result shows that when the dielectric distribution is fined, the photonic band structure will be compressed on the whole and the ground photonic band gap (PBG) closed while the next PBGs shrunk, in conjunction with their position declining in the frequency spectrum. Furthermore, the PBGs in the high zone are much more sensitive than those in low zones.

  20. Determination of conduction and valence band electronic structure of anatase and rutile TiO2

    Indian Academy of Sciences (India)

    Jakub Szlachetko; Katarzyna Michalow-Mauke; Maarten Nachtegaal; Jacinto Sá

    2014-03-01

    Electronic structures of rutile and anatase polymorph of TiO2 were determined by resonant inelastic X-ray scattering measurements and FEFF9.0 calculations. Difference between crystalline structures led to shifts in the rutile Ti -band to lower energy with respect to anatase, i.e., decrease in band gap. Anatase possesses localized states located in the band gap where electrons can be trapped, which are almost absent in the rutile structure. This could well explain the reported longer lifetimes in anatase. It was revealed that HR-XAS is insufficient to study in-depth unoccupied states of investigated materials because it overlooks the shallow traps.

  1. Analysis of photonic band-gap (PBG) structures using the FDTD method

    DEFF Research Database (Denmark)

    Tong, M.S.; Cheng, M.; Lu, Y.L.

    2004-01-01

    In this paper, a number of photonic band-gap (PBG) structures, which are formed by periodic circuit elements printed oil transmission-line circuits, are studied by using a well-known numerical method, the finite-difference time-domain (FDTD) method. The results validate the band-stop filter...

  2. Observation of banded spherulites and lamellar structures by atomic force microscopy

    Institute of Scientific and Technical Information of China (English)

    姜勇; 罗艳红; 范泽夫; 王霞瑜; 徐军; 郭宝华; 李林

    2003-01-01

    Lamellar structures of banded spherulites of poly(ε-caprolactone)/poly(vinyl chloride) (PCL/PVC) blends are observed using tapping mode atomic force microscopy (AFM). The surface of the PCL/PVC banded spherulites presents to be concentric periodic ups and downs. The period of the bands corresponds to the extinction rings under the polarized optical microscopy observation. The lamellae with edge-on orientation in the ridges and the flat-on lamellae in the valleys of the banded spherulites are observed clearly. The twisting between the edge-on and flat-on lamellae is also observed.

  3. Synthesis, physical properties and band structure of non-magnetic Y{sub 3}AlC

    Energy Technology Data Exchange (ETDEWEB)

    Ghule, S.S. [Bharati Vidyapeeth Deemed University College of Engineering, Pune-Satara Road, Pune 411043 (India); Garde, C.S., E-mail: gardecs@gmail.com [Vishwakarma Institute of Information Technology, S. no. 2/3/4, Kondhwa(Bk), Pune 411048 (India); Ramakrishnan, S. [Tata Institute of Fundamental Research, Navynagar, Mumbai 400005 (India); Singh, S. [Indian Institute of Science Education and Research, Dr Homi Bhabha Road, Pashan, Pune 411008 (India); Rajarajan, A.K. [Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Laad, Meena [Symbiosis Institute of Technology (SIT), Symbiosis International University (SIU), Lavale, Pune 412115 (India)

    2016-10-01

    Y{sub 3}AlC has been synthesized by arc melting and subsequent annealing. Rietveld analysis of the powder x-ray diffraction (XRD) data confirms cubic Pm-3m structure. Electrical resistivity (ρ) of Y{sub 3}AlC exhibits metallic behaviour. No sign of superconductivity is observed down to the lowest measurement temperatures of 4.2 K in ρ, and 2 K in magnetic susceptibility (χ) and specific heat (C{sub p}) measurements. The value of the electronic specific heat coefficient γ is 1.36 mJ/K{sup 2} mol from which the density of states (DOS) at the Fermi energy (E{sub F}) is obtained as 0.57 states/eV.unit cell. The value of Debye temperature θ{sub D} is estimated to be 315 K. Electronic band structure calculations of Y{sub 3}AlC reveal a pseudo-gap in the DOS at E{sub F} leading to a small value of 0.5 states/eV unit cell which matches quite well with that obtained from γ. Non-zero value of the DOS indicates metallic behaviour as confirmed by our ρ data. Covalent and ionic bonding seem to co-exist with metallic bonding in Y{sub 3}AlC as indicated by van Arkel- Ketelaar triangle for Zintl-like systems.

  4. Electronic band structure effects in monolayer, bilayer, and hybrid graphene structures

    Science.gov (United States)

    Puls, Conor

    Since its discovery in 2005, graphene has been the focus of intense theoretical and experimental study owing to its unique two-dimensional band structure and related electronic properties. In this thesis, we explore the electronic properties of graphene structures from several perspectives including the magnetoelectrical transport properties of monolayer graphene, gap engineering and measurements in bilayer graphene, and anomalous quantum oscillation in the monolayer-bilayer graphene hybrids. We also explored the device implications of our findings, and the application of some experimental techniques developed for the graphene work to the study of a complex oxide, Ca3Ru2O7, exhibiting properties of strongly correlated electrons. Graphene's high mobility and ballistic transport over device length scales, make it suitable for numerous applications. However, two big challenges remain in the way: maintaining high mobility in fabricated devices, and engineering a band gap to make graphene compatible with logical electronics and various optical devices. We address the first challenge by experimentally evaluating mobilities in scalable monolayer graphene-based field effect transistors (FETs) and dielectric-covered Hall bars. We find that the mobility is limited in these devices, and is roughly inversely proportional to doping. By considering interaction of graphene's Dirac fermions with local charged impurities at the interface between graphene and the top-gate dielectric, we find that Coulomb scattering is responsible for degraded mobility. Even in the cleanest devices, a band gap is still desirable for electronic applications of graphene. We address this challenge by probing the band structure of bilayer graphene, in which a field-tunable energy band gap has been theoretically proposed. We use planar tunneling spectroscopy of exfoliated bilayer graphene flakes demonstrate both measurement and control of the energy band gap. We find that both the Fermi level and

  5. Acoustic band pinning in the phononic crystal plates of anti-symmetric structure

    Institute of Scientific and Technical Information of China (English)

    Cai Chen; Zhu Xue-Feng; Chen Qian; Yuan Ying; Liang Bin; Cheng Jian-Chun

    2011-01-01

    Acoustic bands are studied numerically for a Lamb wave propagating in an anti-symmetric structure of a onedimensional periodic plate by using the method of supercell plane-wave expansion.The results show that all the bands are pinned in pairs at the Brillouin zone boundary as long as the anti-symmetry remains and acoustic band gaps (ABGs) only appear between certain bands.In order to reveal the relationship between the band pinning and the anti-symmetry,the method of eigenmode analysis is introduced to calculate the displacement fields of different plate structures.Further,the method of harmony response analysis is employed to calculate the reference spectra to verify the accuracy of numerical calculations of acoustic band map,and both the locations and widths of ABGs in the acoustic band map are in good agreement with those of the reference spectra.The investigations show that the pinning effect is very sensitive to the anti-symmetry of periodic plates,and by introducing different types of breakages,more ABGs or narrow pass bands will appear,which is meaningful in band gap engineering.

  6. Probing the Spin-Polarized Electronic Band Structure in Monolayer Transition Metal Dichalcogenides by Optical Spectroscopy

    Science.gov (United States)

    Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie

    2017-02-01

    We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2, and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications

  7. Structure and composition of the superconducting phase in alkali iron selenide KyFe1.6+xSe2

    Science.gov (United States)

    Carr, Scott V.; Louca, Despina; Siewenie, Joan; Huang, Q.; Wang, Aifeng; Chen, Xianhui; Dai, Pengcheng

    2014-04-01

    We use neutron diffraction to study the temperature evolution of the average structure and local lattice distortions in insulating and superconducting potassium iron selenide KyFe1.6+xSe2. In the high temperature paramagnetic state, both materials have a single phase with a crystal structure similar to that of the BaFe2As2 family of iron pnictides. While the insulating KyFe1.6+xSe2 forms a √5 ×√5 iron vacancy ordered block antiferromagnetic (AF) structure at low temperature, the superconducting compounds spontaneously phase separate into an insulating part with √5 ×√5 iron vacancy order and a superconducting phase with chemical composition of KzFe2Se2 and BaFe2As2 structure. Therefore, superconductivity in alkaline iron selenides arises from alkali deficient KzFe2Se2 in the matrix of the insulating block AF phase.

  8. Goos-Hänchen shift at the reflection of light from the complex structures composed of superconducting and dielectric layers

    Science.gov (United States)

    Dadoenkova, Yu. S.; Dadoenkova, N. N.; Lyubchanskii, I. L.; Lee, Y. P.

    2015-12-01

    The Goos-Hänchen effect of light reflected from sandwich (three-layered) structures composed of a superconducting YBa2Cu3O7 film and two different dielectric films is investigated theoretically. It has been shown that optical anisotropy of YBa2Cu3O7 film, as well as its positions in the three-layer specimen, strongly effects on the lateral shift values. We have shown that, for all positions of the superconducting film in the three-layered structure, variation of temperature makes possible to control the values of the lateral shift of TE-polarized light at the incidence angles close to pseudo-Brewster angles, whereas for TM-polarized light the lateral shift is only significant at grazing incidence.

  9. Valence and conduction band structure of the quasi-two-dimensional semiconductor Sn S2

    Science.gov (United States)

    Racke, David A.; Neupane, Mahesh R.; Monti, Oliver L. A.

    2016-02-01

    We present the momentum-resolved photoemission spectroscopy of both the valence and the conduction band region in the quasi-two-dimensional van der Waals-layered indirect band gap semiconductor Sn S2 . Using a combination of angle-resolved ultraviolet photoemission and angle-resolved two-photon photoemission (AR-2PPE) spectroscopy, we characterize the band structure of bulk Sn S2 . Comparison with density functional theory calculations shows excellent quantitative agreement in the valence band region and reveals several localized bands that likely originate from defects such as sulfur vacancies. Evidence for a moderate density of defects is also observed by AR-2PPE in the conduction band region, leading to localized bands not present in the computational results. The energetic structure and dispersion of the conduction bands is captured well by the computational treatment, with some quantitative discrepancies remaining. Our results provide a broader understanding of the electronic structure of Sn S2 in particular and van der Waals-layered semiconductors in general.

  10. Disorder enabled band structure engineering of a topological insulator surface

    Science.gov (United States)

    Xu, Yishuai; Chiu, Janet; Miao, Lin; He, Haowei; Alpichshev, Zhanybek; Kapitulnik, A.; Biswas, Rudro R.; Wray, L. Andrew

    2017-02-01

    Three-dimensional topological insulators are bulk insulators with Z2 topological electronic order that gives rise to conducting light-like surface states. These surface electrons are exceptionally resistant to localization by non-magnetic disorder, and have been adopted as the basis for a wide range of proposals to achieve new quasiparticle species and device functionality. Recent studies have yielded a surprise by showing that in spite of resisting localization, topological insulator surface electrons can be reshaped by defects into distinctive resonance states. Here we use numerical simulations and scanning tunnelling microscopy data to show that these resonance states have significance well beyond the localized regime usually associated with impurity bands. At native densities in the model Bi2X3 (X=Bi, Te) compounds, defect resonance states are predicted to generate a new quantum basis for an emergent electron gas that supports diffusive electrical transport.

  11. Experimental determination of excitonic band structures of single-walled carbon nanotubes using circular dichroism spectra

    Science.gov (United States)

    Wei, Xiaojun; Tanaka, Takeshi; Yomogida, Yohei; Sato, Naomichi; Saito, Riichiro; Kataura, Hiromichi

    2016-10-01

    Experimental band structure analyses of single-walled carbon nanotubes have not yet been reported, to the best of our knowledge, except for a limited number of reports using scanning tunnelling spectroscopy. Here we demonstrate the experimental determination of the excitonic band structures of single-chirality single-walled carbon nanotubes using their circular dichroism spectra. In this analysis, we use gel column chromatography combining overloading selective adsorption with stepwise elution to separate 12 different single-chirality enantiomers. Our samples show higher circular dichroism intensities than the highest values reported in previous works, indicating their high enantiomeric purity. Excitonic band structure analysis is performed by assigning all observed Eii and Eij optical transitions in the circular dichroism spectra. The results reproduce the asymmetric structures of the valence and conduction bands predicted by density functional theory. Finally, we demonstrate that an extended empirical formula can estimate Eij optical transition energies for any (n,m) species.

  12. Subharmonic energy gap structure in the Josephson radiation at 35 GHz from a superconducting thin-film microbridge

    DEFF Research Database (Denmark)

    Hansen, Jørn Bindslev; Levinsen, M. T.; Lindelof, Poul Erik;

    1979-01-01

    Nonresonant detection of the Josephson radiation 35 GHz from a superconducting thin-film microbridge is reported. The high frequency and the accuracy of these measurements lead to a new important observation: subharmonic energy gap structure in the detected integral power. The maximum integral po...... power measured was as large as 8×10−11 W. Applied Physics Letters is copyrighted by The American Institute of Physics....

  13. Finite-element simulation of the performance of a superconducting meander structure shielding for a cryogenic current comparator

    Science.gov (United States)

    De Gersem, H.; Marsic, N.; Müller, W. F. O.; Kurian, F.; Sieber, T.; Schwickert, M.

    2016-12-01

    The ferrite core and measuring coil of a cryogenic current comparator have to be shielded against external magnetic fields by a compact, efficient meander structure made of superconducting niobium. A design with minimized material and production costs is only feasible when a highly accurate magnetic field simulator is available. 3D field models become prohibitively large. The cylindrical symmetry of the devices motivates to develop a quasi-3D field solver, exploiting the symmetry while still capable of representing 3D field distributions.

  14. Magnon band structure and magnon density in one-dimensional magnonic crystals

    Science.gov (United States)

    Qiu, Rong-ke; Huang, Te; Zhang, Zhi-dong

    2014-11-01

    By using Callen's Green's function method and the Tyablikov and Anderson-Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the Kx-direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters.

  15. First-principle study of energy band structure of armchair graphene nanoribbons

    Science.gov (United States)

    Ma, Fei; Guo, Zhankui; Xu, Kewei; Chu, Paul K.

    2012-07-01

    First-principle calculation is carried out to study the energy band structure of armchair graphene nanoribbons (AGNRs). Hydrogen passivation is found to be crucial to convert the indirect band gaps into direct ones as a result of enhanced interactions between electrons and nuclei at the edge boundaries, as evidenced from the shortened bond length as well as the increased differential charge density. Ribbon width usually leads to the oscillatory variation of band gaps due to quantum confinement no matter hydrogen passivated or not. Mechanical strain may change the crystal symmetry, reduce the overlapping integral of C-C atoms, and hence modify the band gap further, which depends on the specific ribbon width sensitively. In practical applications, those effects will be hybridized to determine the energy band structure and subsequently the electronic properties of graphene. The results can provide insights into the design of carbon-based devices.

  16. Band Structure Calculation of Si and Ge by Non-Local Empirical Pseudo-Potential Technique

    Institute of Scientific and Technical Information of China (English)

    CHEN Yong; RAVAIOLI Umberto

    2005-01-01

    In this paper, the princ iple of spatial nonlocal empirical pseudopotential and its detailed calculation procedure is presented. Consequently, this technique is employed to calculate the band structuresof Silicon and Germaniun. By comparing the results with photoemission experimental data, the validity and accuracy of this calculation are fully conformed for valence or conductance band,respectively. Thus it can be concluded that the spin-orbit Hamiltonian will only affect the energy band gap and another conductance or valence band structure. Therefore, this nonlocal approach without spin-orbit part is adequate for the device simulation of only one carrier transport such as metal oxide semiconductor field effect transistors (MOSFET)'s, and it can significantly reduce the complication of band structure calculation.

  17. Structural, electronic, elastic and superconducting properties of noble metal nitrides MN{sub 2} (M = Ru, Rh, Pd)

    Energy Technology Data Exchange (ETDEWEB)

    Puvaneswari, S. [Department of Physics, E.M.G. Yadava Women' s College, Madurai, Tamilnadu 625 014 (India); Rajeswarapalanichamy, R., E-mail: rrpcaspd2003@gmail.com [Department of Physics, N.M.S.S. Vellaichamy Nadar College, Madurai, Tamilnadu 625019 (India); Sudha Priyanga, G. [Department of Physics, N.M.S.S. Vellaichamy Nadar College, Madurai, Tamilnadu 625019 (India)

    2015-02-01

    The structural stability, electronic structure, elastic and superconducting properties of noble metal nitrides MN{sub 2} (M = Ru, Rh, Pd) are investigated in tetragonal (P4/mbm), fluorite (Fm3m), orthorhombic (Pnnm), pyrite (Pa-3) and hexagonal (P6/mmm) phases using first principles calculations. The calculated lattice parameters are in good agreement with other theoretical results. Among the considered structures, RhN{sub 2} and PdN{sub 2} are found to be most stable in tetragonal structure, whereas RuN{sub 2} is stable in fluorite structure. A sequence of structural phase transition is predicted under high pressure in these metal nitrides. The electronic structure reveals that these nitrides are metallic. These metal nitrides are found to be covalent, ionic and metallic in the stable phase. The observations show that these metal nitrides are mechanically stable at ambient condition. The superconducting transition temperatures for RuN{sub 2}, RhN{sub 2} and PdN{sub 2} are found to be 1.65 K, 5.01 K and 8.7 K respectively. - Highlights: • Electronic, structural and elastic properties of RuN{sub 2}, RhN{sub 2} and PdN{sub 2} are studied. • A pressure induced structural phase transition is predicted. • Electronic structure reveals that these materials exhibit metallic behavior. • High bulk modulus indicates that RuN{sub 2}, RhN{sub 2} and PdN{sub 2} are superhard materials. • Superconducting temperature values are reported.

  18. Superconductivity from insulating elements under high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Shimizu, Katsuya

    2015-07-15

    Highlights: • Even insulating molecule can become metal and superconductor by pressure with relatively high T{sub c}. • The highest T{sub c} is observed in sulfur with 17 K at 160 GPa. • Hydrogen is the best candidate of the highest T{sub c} element. - Abstract: The insulating and superconducting states would seem to have very different characteristics. Can any insulator become a superconductor? One proven method, doping an insulating material with carriers, can create itinerant states inside the gap between the conduction and valence bands. Another method is to squeeze the structure by applying pressure. Pressure can expand the bandwidth and also narrow the energy band gap. So the first step to turn an insulator into a superconductor is to make it metallic. Here we review our experimental research and results on superconductivity induced by applying pressure to insulating molecular systems such as elemental molecules.

  19. Functional renormalization group study of an 8-band model for the iron arsenides

    Science.gov (United States)

    Honerkamp, Carsten; Lichtenstein, Julian; Maier, Stefan A.; Platt, Christian; Thomale, Ronny; Andersen, Ole Krogh; Boeri, Lilia

    2014-03-01

    We investigate the superconducting pairing instabilities of eight-band models for 1111 iron arsenides. Using a functional renormalization group treatment, we determine how the critical energy scale for superconductivity depends on the electronic band structure. Most importantly, if we vary the parameters from values corresponding to LaFeAsO to SmFeAsO, the pairing scale is strongly enhanced, in accordance with the experimental observation. We analyze the reasons for this trend and compare the results of the eight-band approach to those found using five-band models.

  20. Functional renormalization group study of an eight-band model for the iron arsenides

    Science.gov (United States)

    Lichtenstein, J.; Maier, S. A.; Honerkamp, C.; Platt, C.; Thomale, R.; Andersen, O. K.; Boeri, L.

    2014-06-01

    We investigate the superconducting pairing instabilities of eight-band models for the iron arsenides. Using a functional renormalization group treatment, we determine how the critical energy scale for superconductivity depends on the electronic band structure. Most importantly, if we vary the parameters from values corresponding to LaFeAsO to SmFeAsO, the pairing scale is strongly enhanced, in accordance with the experimental observation. We analyze the reasons for this trend and compare the results of the eight-band approach to those found using five-band models.

  1. B3LYP, BLYP and PBE DFT band structures of the nucleotide base stacks

    Science.gov (United States)

    Szekeres, Zs; Bogár, F.; Ladik, J.

    DFT crystal orbital (band structure) calculations have been performed for the nucleotide base stacks of cytosine, thymine, adenine, and guanine arranged in DNA B geometry. The band structures obtained with PBE, BLYP, and B3LYP functionals are presented and compared to other related experimental and theoretical results. The influence of the quality of the basis set on the fundamental gap values was also investigated using Clementi's double ζ, 6-31G and 6-31G* basis sets.

  2. Theoretical study of band structure of odd-mass 115,117I isotopes

    Science.gov (United States)

    Singh, Dhanvir; Kumar, Amit; Sharma, Chetan; Singh, Suram; Bharti, Arun

    2016-05-01

    By using the microscopic approach of Projected Shell Model (PSM), negative-parity band structures of odd mass neutron-rich 115,117I nuclei have been studied with the deformed single-particle states generated by the standard Nilsson potential. For these isotopes, the band structures have been analyzed in terms of quasi-particles configurations. The phenomenon of back bending in moment of inertia is also studied in the present work.

  3. Electronic- and band-structure evolution in low-doped (Ga,Mn)As

    OpenAIRE

    Yastrubchak, O.; J. Sadowski; Krzyzanowska, H.; Gluba, L.; Zuk, J.; Domagala, J. Z.; Andrearczyk, T.; Wosinski, T.

    2013-01-01

    Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap transition energy with increasing Mn content in very low-doped ...

  4. Superconductivity on the density-wave background with soliton-wall structure

    Energy Technology Data Exchange (ETDEWEB)

    Grigoriev, P.D. [L. D. Landau Institute for Theoretical Physics, Chernogolovka 142432 (Russian Federation)], E-mail: grigorev@itp.ac.ru

    2009-03-01

    Superconductivity (SC) may microscopically coexist with density wave (DW) when the nesting of the Fermi surface (FS) is not perfect. There are, at least, two possible microscopic structures of a DW state with quasi-particle states remaining on the Fermi level and leading to the Cooper instability: (i) the soliton-wall phase and (ii) the small ungapped FS pockets. The dispersion of such quasi-particle states strongly differs from that without DW, and so do the properties of SC on the DW background. The upper critical field H{sub c2} in such an SC state strongly increases as the system approaches the critical pressure, where SC first appears. H{sub c2} may considerably exceed its typical value without DW and has unusual upward curvature as function of temperature. The results obtained explain the experimental observations in layered organic superconductors (TMTSF){sub 2}PF{sub 6} and {alpha}-(BEDT-TTF){sub 2}KHg(SCN){sub 4}.

  5. Initial studies of Bremsstrahlung energy deposition in small-bore superconducting undulator structures in linac environments

    Energy Technology Data Exchange (ETDEWEB)

    Cremer, T.; Tatchyn, R. [Stanford Univ., CA (United States)

    1995-12-31

    One of the more promising technologies for developing minimal-length insertion devices for linac-driven, single-pass Free Electron Lasers (FELs) operating in the x-ray range is based on the use of superconducting (SC) materials. In recent FEL simulations, for example, a bifilar helical SC device with a 2 cm period and 1.8 T field was found to require a 30 m saturation length for operation at 1.5{Angstrom} on a 15 GeV linac, more than 40% shorter than an alternative hybrid/permanent magnet (hybrid/PM) undulator. AT the same time, however, SC technology is known to present characteristic difficulties for insertion device design, both in engineering detail and in operation. Perhaps the most critical problem, as observed, e.g., by Madey and co-workers in their initial FEL experiments, was the frequent quenching induced by scattered electrons upstream of their (bifilar) device. Postulating that this quenching was precipitated by directly-scattered or bremsstrahlung-induced particle energy deposited into the SC material or into material contiguous with it, the importance of numerical and experimental characterizations of this phenomenon for linac-based, user-facility SC undulator design becomes evident. In this paper we discuss selected prior experimental results and report on initial EGS4 code studies of scattered and bremsstrahlung induced particle energy deposition into SC structures with geometries comparable to a small-bore bifilar helical undulator.

  6. Single crystals of superconducting SmFeAsO Hx : Structure and properties

    Science.gov (United States)

    Pisoni, A.; Katrych, S.; Arakcheeva, A.; Verebélyi, T.; Bokor, M.; Huang, P.; Gaál, R.; Matus, P.; Karpinski, J.; Forró, L.

    2016-07-01

    We report the synthesis, structure, and superconducting properties of single crystals of SmFeAsO Hx . The crystals were grown at high pressure and high temperature using a cubic anvil technique. 1H-NMR studies confirm the presence of H atoms in the samples. Single crystal x-ray diffraction analyses demonstrate a remarkable disorder in the S m2O2 layers induced by hydrogen incorporation and reveal that the H positions are compatible with a H2O -like geometry inside the crystals. We have measured the magnetotransport properties of SmFeAsO Hx single crystals with x =0.07 , 0.11, and 0.16 in magnetic field up to 16 T, oriented along the two main crystallographic directions. The results show an increase of the critical temperature with hydrogen content. The zero-temperature upper critical fields and the magnetic anisotropy are calculated as a function of the hydrogen content. SmFeAsO Hx crystals present significantly higher upper critical fields and magnetic anisotropies compared to SmFeAs O1 -xFx compounds.

  7. Upgraded phase control system for superconducting low-velocity accelerating structures

    Energy Technology Data Exchange (ETDEWEB)

    Added, N. (Sao Paulo Univ., SP (Brazil). Dept. de Fisica Nuclear); Clifft, B.E.; Shepard, K.W. (Argonne National Lab., IL (United States))

    1992-01-01

    Microphonic-induced fluctuations in the RF eigenfrequency of superconducting (SC) slow-wave structures must be compensated by a fast-tuning system in order to control the RF phase. The tuning system must handle a reactive power proportional to the product of the frequency range and the RF energy content of the Rf cavity. The fast tuner for the SC resonators in the ATLAS heavy-ion linac is a voltage-controlled reactance based on an array of PIN diodes operating immersed in liquid nitrogen. This paper discusses recent upgrades to the ATLAS fast tuner which can now provide as much as 30 KVA of reactive tuning capability with a real RF power loss of less than 300 watts. The design was guided by numerical modeling of all elements of the device. Also discussed is the RF coupler which can couple 30 KW from 77 K tuner to a 42 K resonant cavity with less than 2 W of RF loss into 4.2 K.

  8. Upgraded phase control system for superconducting low-velocity accelerating structures

    Energy Technology Data Exchange (ETDEWEB)

    Added, N. [Sao Paulo Univ., SP (Brazil). Dept. de Fisica Nuclear; Clifft, B.E.; Shepard, K.W. [Argonne National Lab., IL (United States)

    1992-09-01

    Microphonic-induced fluctuations in the RF eigenfrequency of superconducting (SC) slow-wave structures must be compensated by a fast-tuning system in order to control the RF phase. The tuning system must handle a reactive power proportional to the product of the frequency range and the RF energy content of the Rf cavity. The fast tuner for the SC resonators in the ATLAS heavy-ion linac is a voltage-controlled reactance based on an array of PIN diodes operating immersed in liquid nitrogen. This paper discusses recent upgrades to the ATLAS fast tuner which can now provide as much as 30 KVA of reactive tuning capability with a real RF power loss of less than 300 watts. The design was guided by numerical modeling of all elements of the device. Also discussed is the RF coupler which can couple 30 KW from 77 K tuner to a 42 K resonant cavity with less than 2 W of RF loss into 4.2 K.

  9. Superconductivity Bordering Rashba Type Topological Transition

    Energy Technology Data Exchange (ETDEWEB)

    Jin, M. L.; Sun, F.; Xing, L. Y.; Zhang, S. J.; Feng, S. M.; Kong, P. P.; Li, W. M.; Wang, X. C.; Zhu, J. L.; Long, Y. W.; Bai, H. Y.; Gu, C. Z.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Mao, H. K.; Jin, C. Q.

    2017-01-04

    Strong spin orbital interaction (SOI) can induce unique quantum phenomena such as topological insulators, the Rashba effect, or p-wave superconductivity. Combining these three quantum phenomena into a single compound has important scientific implications. Here we report experimental observations of consecutive quantum phase transitions from a Rashba type topological trivial phase to topological insulator state then further proceeding to superconductivity in a SOI compound BiTeI tuned via pressures. The electrical resistivity measurement with V shape change signals the transition from a Rashba type topological trivial to a topological insulator phase at 2 GPa, which is caused by an energy gap close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature TC of 5.3 K. Structure refinements indicate that the consecutive phase transitions are correlated to the changes in the Bi–Te bond and bond angle as function of pressures. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.

  10. Superconductivity Bordering Rashba Type Topological Transition

    Science.gov (United States)

    Jin, M. L.; Sun, F.; Xing, L. Y.; Zhang, S. J.; Feng, S. M.; Kong, P. P.; Li, W. M.; Wang, X. C.; Zhu, J. L.; Long, Y. W.; Bai, H. Y.; Gu, C. Z.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Mao, H. K.; Jin, C. Q.

    2017-01-01

    Strong spin orbital interaction (SOI) can induce unique quantum phenomena such as topological insulators, the Rashba effect, or p-wave superconductivity. Combining these three quantum phenomena into a single compound has important scientific implications. Here we report experimental observations of consecutive quantum phase transitions from a Rashba type topological trivial phase to topological insulator state then further proceeding to superconductivity in a SOI compound BiTeI tuned via pressures. The electrical resistivity measurement with V shape change signals the transition from a Rashba type topological trivial to a topological insulator phase at 2 GPa, which is caused by an energy gap close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature TC of 5.3 K. Structure refinements indicate that the consecutive phase transitions are correlated to the changes in the Bi–Te bond and bond angle as function of pressures. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.

  11. Dual-Band Terahertz Left-Handed Metamaterial with Fishnet Structure

    Institute of Scientific and Technical Information of China (English)

    DU Qiu-Jiao; LIU Jin-Song; WANG Ke-Jia; YI Xu-Nong; YANG Hong-Wu

    2011-01-01

    We present the design of a dual-band left-handed metamaterial with fishnet structure in the terahertz regime. Its left-handed properties are described by the retrieved effective electromagnetic parameters. We introduce an equivalent circuit which offers a theoretical explanation for the left-handed behavior of the dual-band fishnet metamaterial, and investigate its losses receiving higher figure of merit. The design is beneficial to the development of frequency agile and broadband THz materials and devices. The dual-band fishnet metamaterial can be extended to infrared and optical frequency ranges by regulating the structural parameters.

  12. Realization of Band-Notch UWB Monopole Antenna Using AMC Structure

    Directory of Open Access Journals (Sweden)

    Pradeep Kumar

    2013-06-01

    Full Text Available This article presents the design, simulation and testing of an Ultra Wide Band (UWB planar monopole antenna with WLAN band-notch characteristic. The proposed antenna consists, the combination of planar monopole antenna with partial ground and a pair of AMC structures. The AMC structure used for the design is mushroom-like. Design equation of EBG parameters is also proposed for FR4 substrate using transmission line model. Using proposed equations, Mushroom-like EBG structure is integrated along the feed line of a monopole antenna for WLAN (5 GHz – 6 GHz band rejection. TheCurrent distribution and equivalent circuit model of antenna is used to explain band-notch characteristic of EBG resonator. The proposed antenna is fabricated on an FR4 substrate with a thickness of 1.6 mmand εr = 4.4. The measured VSWR characteristic is less than 2 for complete UWB band except for WLAN band i.e. 5 GHz – 6 GHz. The gain of the proposed structure is around 2 dBi – 6.7 dBi for complete UWBband except for WLAN band where it is reduced to -4 dBi. The measured radiation pattern of proposed antenna is omnidirectional along H plane and bidirectional in E plane. A nearly constant group delaywith variations < 2ns, except for the notched bandwidth makes proposed antenna suitable for UWB application.

  13. Superconducting optical modulator

    Science.gov (United States)

    Bunt, Patricia S.; Ference, Thomas G.; Puzey, Kenneth A.; Tanner, David B.; Tache, Nacira; Varhue, Walter J.

    2000-12-01

    An optical modulator based on the physical properties of high temperature superconductors has been fabricated and tested. The modulator was constructed form a film of Yttrium Barium Copper Oxide (YBCO) grown on undoped silicon with a buffer layer of Yttria Stabilized Zirconia. Standard lithographic procedures were used to pattern the superconducting film into a micro bridge. Optical modulation was achieved by passing IR light through the composite structure normal to the micro bridge and switching the superconducting film in the bridge region between the superconducting and non-superconducting states. In the superconducting state, IR light reflects from the superconducting film surface. When a critical current is passed through the micro bridge, it causes the film in this region to switch to the non-superconducting state allowing IR light to pass through it. Superconducting materials have the potential to switch between these two states at speeds up to 1 picosecond using electrical current. Presently, fiber optic transmission capacity is limited by the rate at which optical data can be modulated. The superconducting modulator, when combined with other components, may have the potential to increase the transmission capacity of fiber optic lines.

  14. Superconductivity in the topological semimetal YPtBi

    Science.gov (United States)

    Butch, Nicholas

    2012-02-01

    Superconductivity was recently discovered in the half Heusler compound YPtBi. Electrical resistivity and Hall data provide compelling evidence that supports the idea that band structure calculations are correct and that YPtBi is indeed a semimetal with nontrivial topology. The low-temperature superconductivity emerges from a remarkable normal state with an extremely low carrier density, no crystalline inversion symmetry, and strong band inversion. I will discuss the normal state properties of YPtBi and details of its superconducting state, and compare them to the characteristics of other potential topological superconductors. This research was performed at the University of Maryland, College Park in collaboration with Paul Syers, Kevin Kirshenbaum, Andrew P. Hope, and Johnpierre Paglione.

  15. Low-frequency photonic band structures in graphene-like triangular metallic lattice

    Science.gov (United States)

    Wang, Kang

    2016-11-01

    We study the low frequency photonic band structures in triangular metallic lattice, displaying Dirac points in the frequency spectrum, and constructed upon the lowest order regular polygonal tiles. We show that, in spite of the unfavourable geometrical conditions intrinsic to the structure symmetry, the lowest frequency photonic bands are formed by resonance modes sustained by local structure patterns, with the corresponding electric fields following a triangular distribution at low structure filling rate and a honeycomb distribution at high filling rate. For both cases, the lowest photonic bands, and thus the plasma gap, can be described in the framework of a tight binding model, and analysed in terms of local resonance modes and their mutual correlations. At high filling rate, the Dirac points and their movement following the structure deformation are described in the same framework, in relation with local structure patterns and their variations, as well as the particularity of the metallic lattice that enhances the topological anisotropy.

  16. Photonic band gaps in materials with triply periodic surfaces and related tubular structures

    NARCIS (Netherlands)

    Michielsen, K; Kole, JS

    2003-01-01

    We calculate the photonic band gap of triply periodic bicontinuous cubic structures and of tubular structures constructed from the skeletal graphs of triply periodic minimal surfaces. The effect of the symmetry and topology of the periodic dielectric structures on the existence and the characteristi

  17. Photonic band structure of ZnO photonic crystal slab laser

    CERN Document Server

    Yamilov, A; Cao, H

    2005-01-01

    We recently reported on the first realization of ultraviolet photonic crystal laser based on zinc oxide [Appl. Phys. Lett. {\\bf 85}, 3657 (2004)]. Here we present the details of structural design and its optimization. We develop a computational super-cell technique, that allows a straightforward calculation of the photonic band structure of ZnO photonic crystal slab on sapphire substrate. We find that despite of small index contrast between the substrate and the photonic layer, the low order eigenmodes have predominantly transverse-electric (TE) or transverse-magnetic (TM) polarization. Because emission from ZnO thin film shows strong TE preference, we are able to limit our consideration to TE bands, spectrum of which can possess a complete photonic band gap with an appropriate choice of structure parameters. We demonstrate that the geometry of the system may be optimized so that a sizable band gap is achieved.

  18. Hg Substitution Effect on Superconductivity and Crystal Structure of MgB2

    Institute of Scientific and Technical Information of China (English)

    Ya-Jing Cui; Yong-Liang Chen; Ye Yang; Yong Zhang; Cui-Hua Cheng; Yong Zhao

    2008-01-01

    Polycrystalline Mg1-xHgxB2 samples with x=0, 1%, 2.5%, 5%, 7.5%, and 10% have been synthe- sized by solid-state reaction. Different from the substitu- tion effect of Al, C, Li, etc. on crystal structure of MgB2, Hg substitution for Mg results in an increase of the lattice constant in both a and c directions. The super- conductivity of MgB2 is also suppressed by Hg substi- tution. The observed suppression of super- conductivity by Hg substitution is discussed in terms of the interband impurity scattering effect in two-band superconductors.

  19. Polar semiconductor heterojunction structure energy band diagram considerations

    Science.gov (United States)

    Lin, Shuxun; Wen, Cheng P.; Wang, Maojun; Hao, Yilong

    2016-03-01

    The unique nature of built-in electric field induced positive/negative charge pairs of polar semiconductor heterojunction structure has led to a more realistic device model for hexagonal III-nitride HEMT. In this modeling approach, the distribution of charge carriers is dictated by the electrostatic potential profile instead of Femi statistics. The proposed device model is found suitable to explain peculiar properties of GaN HEMT structures, including: (1) Discrepancy in measured conventional linear transmission line model (LTLM) sheet resistance and contactless sheet resistance of GaN HEMT with thin barrier layer. (2) Below bandgap radiation from forward biased Nickel Schottky barrier diode on GaN HEMT structure. (3) GaN HEMT barrier layer doping has negligible effect on transistor channel sheet charge density.

  20. Exploration of stable compounds, crystal structures, and superconductivity in the Be-H system

    Directory of Open Access Journals (Sweden)

    Shuyin Yu

    2014-10-01

    Full Text Available Using first-principles variable-composition evolutionary methodology, we explored the high-pressure structures of beryllium hydrides between 0 and 400 GPa. We found that BeH2 remains the only stable compound in this pressure range. The pressure-induced transformations are predicted as I b a m → P 3 ̄ m 1 → R 3 ̄ m → C m c m → P 4 / n m m , which occur at 24, 139, 204 and 349 GPa, respectively. P 3 ̄ m 1 and R 3 ̄ m structures are layered polytypes based on close packings of H atoms with Be atoms filling all octahedral voids in alternating layers. Cmcm and P4/nmm contain two-dimensional triangular networks with each layer forming a kinked slab in the ab-plane. P 3 ̄ m 1 and R 3 ̄ m are semiconductors while Cmcm and P4/nmm are metallic. We have explored superconductivity of both metal phases, and found large electron-phonon coupling parameters of λ = 0.63 for Cmcm with a Tc of 32.1-44.1 K at 250 GPa and λ = 0.65 for P4/nmm with a Tc of 46.1-62.4 K at 400 GPa. The dependence of Tc on pressure indicates that Tc initially increases to a maximum of 45.1 K for Cmcm at 275 GPa and 97.0 K for P4/nmm at 365 GPa, and then decreases with increasing pressure for both phases.

  1. Structural and superconducting properties of YBa2Cu3-xMxOy (M=Ag, Al

    Directory of Open Access Journals (Sweden)

    S Falahati

    2009-08-01

    Full Text Available   Samples of YBa2Cu3-xAgxOy with x=0, 0.1, 0.15, 0.2, 0.3 and samples of YBa2Cu3-xAlxOy with x=0, 0.01, 0.02, 0.03 and 0.045 are prepared by the sol-gel method. Structural and superconducting properties of samples are studied by electrical resistivity (R-T, X-ray diffraction (XRD and scanning electron microscopy (SEM. All the samples show transition to superconducting state and the transition temperatures of the samples increased with increasing Ag doping up to x=0.15. R-T measurements show a small decrease of TC (zero with increasing Al doping up to x=0.02, and followed by a faster decrease with increasing doping concentration. YBCO grains are better linked with increasing Ag doping. So, Ag has positive effects in superconducting properties of YBCO. The crystal structure of samples was refined by MAUD. These results show tha, Ag is substituted for Cu(1 in YBCO. According to these analysis, we introduce x=0.15 as the optimum value for doping concentration .

  2. Prediction of phonon-mediated superconductivity in borophene

    Science.gov (United States)

    Gao, Miao; Li, Qi-Zhi; Yan, Xun-Wang; Wang, Jun

    2017-01-01

    Superconductivity in two-dimensional compounds is widely studied, not only because of its application in constructing nano-superconducting devices, but also for general scientific interest. Very recently, borophene (a two-dimensional boron sheet) has been successfully grown on the Ag(111) surface, through direct evaporation of a pure boron source. The experiment unveiled two types of borophene structures, namely β12 and χ3. Herein, we employed density-functional first-principles calculations to investigate the electron-phonon coupling and superconductivity in both structures of borophene. The band structures of β12 and χ3 borophenes exhibit inherent metallicity. We found that electron-phonon coupling constants in the two compounds are larger than that in MgB2. The superconducting transition temperatures were determined to be 18.7 K and 24.7 K through the McMillian-Allen-Dynes formula. These temperatures are much higher than the theoretically predicted 8.1 K and experimentally observed 7.4 K superconductivity in graphene. Our findings will enrich nano-superconducting device applications and boron-related materials science.

  3. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Hofstadter's Butterfly and Phase Transition of Checkerboard Superconducting Network in a Magnetic Field

    Science.gov (United States)

    Hou, Jing-Min; Tian, Li-Jim

    2010-03-01

    We study the magnetic effect of the checkerboard superconducting wire network. Based on the de Gennes-Alexader theory, we obtain difference equations for superconducting order parameter in the wire network. Through solving these difference equations, we obtain the eigenvalues, linked to the coherence length, as a function of magnetic field. The diagram of eigenvalues shows a fractal structure, being so-called Hofstadter's butterfly. We also calculate and discuss the dependence of the transition temperature of the checkerboard superconducting wire network on the applied magnetic field, which is related to up-edge of the Hofstadter's butterfly spectrum.

  4. The C-Band accelerating structures for SPARC photoinjector energy upgrade

    Science.gov (United States)

    Alesini, D.; Boni, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M.; Gallo, A.; Lollo, V.; Marcellini, F.; Palumbo, L.; Spizzo, V.; Mostacci, A.; Campogiani, G.; Persichelli, S.; Enomoto, A.; Higo, T.; Kakihara, K.; Kamitani, T.; Matsumoto, S.; Sugimura, T.; Yokoyama, K.; Verdú-Andrés, S.

    2013-05-01

    The use of C-Band structures for electron acceleration and production of high quality beams has been proposed and adopted in several linac projects all over the world. The two main projects that adopted such type of structures are the Japanese Free Electron Laser (FEL) project in Spring-8 and the SwissFEL project at Paul Scherrer Institute (PSI). Also the energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. The paper presents the design criteria of the structures, the realization procedure and the low and high power RF test results on a prototype. The high power tests have been carried out by the Frascati INFN Laboratories in close collaboration with the Japanese Laboratory KEK. Experimental results confirmed the feasibility of the operation of the prototype at 50 MV/m with about 10-6 breakdowns per pulse per meter. Such high gradients have not been reached before in C-Band systems and demonstrated the possibility to use C-band accelerators, if needed, at such high field level. The results of the internal inspection of the structure after the high power test are also presented.

  5. Electronic Band Structures of TiO2 with Heavy Nitrogen Doping

    Institute of Scientific and Technical Information of China (English)

    XUE Jinbo; LI Qi; LIANG Wei; SHANG Jianku

    2008-01-01

    The first-principles density-functional calculation was conducted to investigate the electronic band structures of titanium dioxide with heavy nitrogen doping (TiO2-xNx).The calculation results indicate that when x≤0.25,isolated N 2p states appear above the valence-band maximum of TiO2 without a band-gap narrowing between O 2p and Ti 3d states.When x≥0.50,an obvious band gap narrowing between O 2p and Ti 3d states was observed along with the existence of isolated N 2p states above the valence-band of TiO2,indicating that the mechanism proposed by Asahi et al operates under heavy nitrogen doping condition.

  6. Reducing support loss in micromechanical ring resonators using phononic band-gap structures

    Science.gov (United States)

    Hsu, Feng-Chia; Hsu, Jin-Chen; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin

    2011-09-01

    In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

  7. Berry phase and band structure analysis of the Weyl semimetal NbP

    Science.gov (United States)

    Sergelius, Philip; Gooth, Johannes; Bäßler, Svenja; Zierold, Robert; Wiegand, Christoph; Niemann, Anna; Reith, Heiko; Shekhar, Chandra; Felser, Claudia; Yan, Binghai; Nielsch, Kornelius

    2016-01-01

    Weyl semimetals are often considered the 3D-analogon of graphene or topological insulators. The evaluation of quantum oscillations in these systems remains challenging because there are often multiple conduction bands. We observe de Haas-van Alphen oscillations with several frequencies in a single crystal of the Weyl semimetal niobium phosphide. For each fundamental crystal axis, we can fit the raw data to a superposition of sinusoidal functions, which enables us to calculate the characteristic parameters of all individual bulk conduction bands using Fourier transform with an analysis of the temperature and magnetic field-dependent oscillation amplitude decay. Our experimental results indicate that the band structure consists of Dirac bands with low cyclotron mass, a non-trivial Berry phase and parabolic bands with a higher effective mass and trivial Berry phase. PMID:27667203

  8. Reducing support loss in micromechanical ring resonators using phononic band-gap structures

    Energy Technology Data Exchange (ETDEWEB)

    Hsu, Feng-Chia; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin [Industrial Technology Research Institute-South, Tainan 709, Taiwan (China); Hsu, Jin-Chen, E-mail: fengchiahsu@itri.org.t, E-mail: hsujc@yuntech.edu.t [Department of Mechanical Engineering, National Yunlin University of Science and Technology, Douliou, Yunlin 64002, Taiwan (China)

    2011-09-21

    In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

  9. Optimization of superconducting tiling pattern for superconducting bearings

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Hinsdale, IL)

    1996-01-01

    An apparatus and method for reducing magnetic field inhomogeneities which produce rotational loss mechanisms in high temperature superconducting magnetic bearings. Magnetic field inhomogeneities are reduced by dividing high temperature superconducting structures into smaller structures, and arranging the smaller structures into tiers which stagger the magnetic field maximum locations of the smaller structures.

  10. Superlattice band structure: New and simple energy quantification condition

    Energy Technology Data Exchange (ETDEWEB)

    Maiz, F., E-mail: fethimaiz@gmail.com [University of Cartage, Nabeul Engineering Preparatory Institute, Merazka, 8000 Nabeul (Tunisia); King Khalid University, Faculty of Science, Physics Department, P.O. Box 9004, Abha 61413 (Saudi Arabia)

    2014-10-01

    Assuming an approximated effective mass and using Bastard's boundary conditions, a simple method is used to calculate the subband structure for periodic semiconducting heterostructures. Our method consists to derive and solve the energy quantification condition (EQC), this is a simple real equation, composed of trigonometric and hyperbolic functions, and does not need any programming effort or sophistic machine to solve it. For less than ten wells heterostructures, we have derived and simplified the energy quantification conditions. The subband is build point by point; each point presents an energy level. Our simple energy quantification condition is used to calculate the subband structure of the GaAs/Ga{sub 0.5}Al{sub 0.5}As heterostructures, and build its subband point by point for 4 and 20 wells. Our finding shows a good agreement with previously published results.

  11. Band gap formation and control in coupled periodic ferromagnetic structures

    Science.gov (United States)

    Morozova, M. A.; Sharaevskaya, A. Yu.; Sadovnikov, A. V.; Grishin, S. V.; Romanenko, D. V.; Beginin, E. N.; Sharaevskii, Yu. P.; Nikitov, S. A.

    2016-12-01

    We demonstrate theoretically and experimentally the formation of additional bandgaps in the spectrum of spin waves in coupled magnonic crystals. We present the analytical model, which reveals the mechanism of bandgaps formation in coupled structures. In particular, the formation of one, two, or three bandgaps in the region of the first Bragg resonance is demonstrated and control of its characteristics by the variation of the complex coupling coefficient between magnonic crystals is shown. The spatially-resolved Brillouin light scattering spectroscopy and microwave measurements demonstrate the bandgap splitting in the spin-wave spectrum. The main advantage of proposed coupled structure, as compared to the conventional magnonic crystal, is the tunability of multiple bandgaps in the spin-wave spectrum, which enables potential applications in the frequency selective magnonic devices.

  12. Band structures of 4f and 5f materials studied by angle-resolved photoelectron spectroscopy

    Science.gov (United States)

    Fujimori, Shin-ichi

    2016-04-01

    Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ∼ 7~\\text{eV} ) or high-energy synchrotron radiations (hν ≳ 400~\\text{eV} ) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of \\text{Ce}M\\text{I}{{\\text{n}}5} (M=\\text{Rh} , \\text{Ir} , and \\text{Co} ) and \\text{YbR}{{\\text{h}}2}\\text{S}{{\\text{i}}2} with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant \\text{U}~5f compounds such as \\text{UFeG}{{\\text{a}}5} , their electronic structures can be well-described by the band-structure calculation assuming that all \\text{U}~5f electrons are itinerant. In contrast, the band structures of localized \\text{U}~5f compounds such as \\text{UP}{{\\text{d}}3} and \\text{U}{{\\text{O}}2} are essentially explained by the localized model that treats \\text{U}~5f electrons as localized core states. In regards to heavy fermion \\text{U} -based compounds such as the hidden-order compound \\text{UR}{{\\text{u}}2}\\text{S}{{\\text{i}}2} , their electronic structures exhibit complex behaviors. Their overall band structures

  13. Topological confinement and superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Al-hassanieh, Dhaled A [Los Alamos National Laboratory; Batista, Cristian D [Los Alamos National Laboratory

    2008-01-01

    We derive a Kondo Lattice model with a correlated conduction band from a two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence of a robust pairing mechanism in a model that only contains repulsive interactions. The mechanism is due to topological confinement and results from the interplay between antiferromagnetism and delocalization. By using Density-Matrix-Renormalization-Group (DMRG) we demonstrate that this mechanism leads to dominant superconducting correlations in aID-system.

  14. Mixed-mu superconducting bearings

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Hinsdale, IL); Mulcahy, Thomas M. (Western Springs, IL)

    1998-01-01

    A mixed-mu superconducting bearing including a ferrite structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet structure. The ferrite structure is levitated by said stationary permanent magnet structure.

  15. Magnon band structure and magnon density in one-dimensional magnonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Rong-ke, E-mail: rkqiu@163.com [Shenyang University of Technology, Shenyang 110870 (China); Huang, Te [Shenyang University of Technology, Shenyang 110870 (China); Zhang, Zhi-dong [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2014-11-15

    By using Callen's Green's function method and the Tyablikov and Anderson–Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the K{sub x}-direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters. - Highlights: • A quantum approach has been developed to study the magnon band of magnonic crystals. • The separate and overlapping magnon bands of magnetic superlattices are investigated. • The results are beneficial for the design of gigahertz-range spin-wave filters.

  16. Tunable band structures of polycrystalline graphene by external and mismatch strains

    Institute of Scientific and Technical Information of China (English)

    Jiang-Tao Wu; Xing-Hua Shi; Yu-Jie Wei

    2012-01-01

    Lacking a band gap largely limits the application of graphene in electronic devices.Previous study shows that grain boundaries (GBs) in polycrystalline graphene can dramatically alter the electrical properties of graphene.Here,we investigate the band structure of polycrystalline graphene tuned by externally imposed strains and intrinsic mismatch strains at the GB by density functional theory (DFT) calculations.We found that graphene with symmetrical GBs typically has zero band gap even with large uniaxial and biaxial strain.However,some particular asymmetrical GBs can open a band gap in graphene and their band structures can be substantially tuned by external strains.A maximum band gap about 0.19 eV was observed in matched-armchair GB (5,5) | (3,7) with a misorientation of θ =13° when the applied uniaxial strain increases to 9%.Although mismatch strain is inevitable in asymmetrical GBs,it has a small influence on the band gap of polycrystalline graphene.

  17. Design of UWB monopole antenna with dual notched bands using one modified electromagnetic-bandgap structure.

    Science.gov (United States)

    Liu, Hao; Xu, Ziqiang

    2013-01-01

    A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR WiMAX) and the wireless local area network (WLAN) at 3.5 GHz and 5.5 GHz, respectively.

  18. Study on electro-optic properties of two-dimensional PLZT photonic crystal band structure

    Institute of Scientific and Technical Information of China (English)

    TONG Kai; WU Xiao-gang; WANG Mei-ting

    2011-01-01

    The band characteristics of two-dimensional (2D) lead lanthanum zirconate titanate (PLZT) photonic cystals are analyzed by finite element method. The electro-optic effect of PLZT can cause the refractive index change when it is imposed by the applied electric field, and the band structure of 2D photonic crystals based on PLZT varies accordingly. The effect of the applied electric field on the structural characteristics of the first and second band gaps in 2D PLZT photonic crystals is analyzed in detail. And the results show that for each band gap, the variations of start wavelength, cut-off wavelength and bandwidth are proportional to quadratic of the electric field.

  19. A short remark on the band structure of free-edge platonic crystals

    Science.gov (United States)

    Smith, Michael J. A.; Meylan, Michael H.; McPhedran, Ross C.; Poulton, Chris G.

    2014-10-01

    A corrected version of the multipole solution for a thin plate perforated in a doubly periodic fashion is presented. It is assumed that free-edge boundary conditions are imposed at the edge of each cylindrical inclusion. The solution procedure given here exploits a well-known property of Bessel functions to obtain the solution directly, in contrast to the existing incorrect derivation. A series of band diagrams and an updated table of values are given for the resulting system (correcting known publications on the topic), which shows a spectral band at low frequency for the free-edge problem. This is in contrast to clamped-edge boundary conditions for the same biharmonic plate problem, which features a low-frequency band gap. The numerical solution procedure outlined here is also simplified relative to earlier publications, and exploits the spectral properties of complex-valued matrices to determine the band structure of the structured plate.

  20. Deformation analysis of ferrite/pearlite banded structure under uniaxial tension using digital image correlation

    Science.gov (United States)

    Zhang, Xiaochuan; Wang, Yong; Yang, Jia; Qiao, Zhixia; Ren, Chunhua; Chen, Cheng

    2016-10-01

    The ferrite/pearlite banded structure causes the anisotropic behavior of steel. In this paper, digital image correlation (DIC) was used to analyze the micro deformation of this microstructure under uniaxial tension. The reliability of DIC for this application was verified by a zero-deformation experiment. The results show that the performance of DIC can satisfy the requirements of the tensile deformation measurement. Then, two uniaxial tensile tests in different directions (longitudinal direction and transverse direction) were carried out and DIC was used to measure the micro deformation of the ferrite/pearlite banded structure. The measured results show that the ferrite bands undergo the main deformation in the transverse tension, which results in the relatively weaker tensile properties in the transverse direction than in the longitudinal direction. This work is useful to guide the modification of the bands morphology and extend the application scope of DIC.

  1. Photonic band structures of two-dimensional photonic crystals with deformed lattices

    Institute of Scientific and Technical Information of China (English)

    Cai Xiang-Hua; Zheng Wan-Hua; Ma Xiao-Tao; Ren Gang; Xia Jian-Bai

    2005-01-01

    Using the plane-wave expansion method, we have calculated and analysed the changes of photonic band structures arising from two kinds of deformed lattices, including the stretching and shrinking of lattices. The square lattice with square air holes and the triangular lattice with circular air holes are both studied. Calculated results show that the change of lattice size in some special ranges can enlarge the band gap, which depends strongly on the filling factor of air holes in photonic crystals; and besides, the asymmetric band edges will appear with the broken symmetry of lattices.

  2. Analysis of two-dimensional photonic band gap structure with a rhombus lattice

    Institute of Scientific and Technical Information of China (English)

    Limei Qi; Ziqiang Yang; Xi Gao; Zheng Liang

    2008-01-01

    @@ The relative band gap for a rhombus lattice photonic crystal is studied by plane wave expansion method and high frequency structure simulator (HFSS) simulation. General wave vectors in the first Briliouin zone are derived. The relative band gap as a function of air-filling factor and background material is investigated, respectively, and the nature of photonic band gap for different lattice angles is analyzed by the distribution of electric energy. These results would provide theoretical instruction for designing optical integrated devices using photonic crystal with a rhombus lattice.

  3. Pathway to Oxide Photovoltaics via Band-Structure Engineering of SnO

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Haowei; Bikowski, Andre; Zakutayev, Andriy; Lany, Stephan

    2016-10-01

    All-oxide photovoltaics could open rapidly scalable manufacturing routes, if only oxide materials with suitable electronic and optical properties were developed. SnO has exceptional doping and transport properties among oxides, but suffers from a strongly indirect band gap. Here, we address this shortcoming by band-structure engineering through isovalent but heterostructural alloying with divalent cations (Mg, Ca, Sr, and Zn). Using first-principles calculations, we show that suitable band gaps and optical properties close to that of direct semiconductors are achievable, while the comparatively small effective masses are preserved in the alloys. Initial thin film synthesis and characterization support the feasibility of the approach.

  4. Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, Nadir; Sweeney, Stephen [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom); Hosea, Jeff [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, UK and Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor Bahru 81310 (Malaysia); Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Stolz, Wolfgang [Material Sciences Center and Faculty of Physics, Philipps-University, 35032 Marburg (Germany); Kunert, Bernerdette [NAsP III/V GmbH, Am Knechtacker 19, 35041 Marburg (Germany)

    2013-12-04

    We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates.

  5. Study of periodic band gap structure of the magnetized plasma photonic crystals

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hai-feng; MA Li; LIU Shao-bin

    2009-01-01

    The characteristics of the periodic band gaps of the one dimension magnetized plasma photonic crystals are studied with the piecewise linear current density recursive convolution (PLCDRC) finite-differential time-domain (FDTD) method. In fre-quency-domain, the transmission coefficients of electromagnetic Gaussian pulses are computed, and the effects of the periodic structure constant, plasma layer thickness and parameters of plasma on the properties of periodic band gaps of magnetized photonic crystals are analyzed. The results show that the periodic band gaps depend strongly on the plasma parameters.

  6. Band structure in doubly-odd nuclei with mass around 130

    Energy Technology Data Exchange (ETDEWEB)

    Higashiyama, K [Department of Physics, University of Tokyo, Hongo, Tokyo 113-0033 (Japan); Yoshinaga, N [Department of Physics, Saitama University, Saitama City 338-8570 (Japan)

    2006-10-10

    Nuclear structure of the doublet bands in the doubly-odd nuclei with mass A {approx} 130 is studied in terms of a pair-truncated shell model. The model reproduces quite well the energy levels of the doublet bands and the electromagnetic transitions. The doublet bands turn out to be realized by the chopsticks-like motion of two angular momenta of the unpaired neutron and the unpaired proton, weakly coupled with the quadrupole collective excitations of the even-even part of the nucleus.

  7. Engineering the electronic structure and band gap of boron nitride nanoribbon via external electric field

    Science.gov (United States)

    Chegel, Raad

    2016-06-01

    By using the third nearest neighbor modified tight binding (3NN-TB) method, the electronic structure and band gap of BNNRs under transverse electric fields are explored. The band gap of the BNNRs has a decreasing with increasing the intensity of the applied electric field, independent on the ribbon edge types. Furthermore, an analytic model for the dependence of the band gap in armchair and zigzag BNNRs on the electric field is proposed. The reduction of E g is similar for some N a armchair and N z zigzag BNNRs independent of their edges.

  8. The LDA+U calculation of electronic band structure of GaAs

    Science.gov (United States)

    Bahuguna, B. P.; Sharma, R. O.; Saini, L. K.

    2016-05-01

    We present the electronic band structure of bulk gallium arsenide (GaAs) using first principle approach. A series of calculations has been performed by applying norm-conserving pseudopotentials and ultrasoft non-norm-conserving pseudopotentials within the density functional theory. These calculations yield too small band gap as compare to experiment. Thus, we use semiemperical approach called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U), which is quite effective in order to describe the band gap of GaAs.

  9. Theoretical study of superconducting proximity effect in single and multi-layered graphene

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Masahiko, E-mail: m-hayashi@ed.akita-u.ac.j [Faculty of Education and Human Studies, Akita University, Akita 010-8502 (Japan); JST-CREST, Kawaguchi, Saitama 332-0012 (Japan); Yoshioka, Hideo [Department of Physics, Nara Women' s University, Nara 630-8506 (Japan); Kanda, Akinobu [Institute of Physics, University of Tsukuba, Tsukuba 305-8571 (Japan)

    2010-12-15

    Theoretical analysis of superconducting current in graphite thin films (or graphene) in proximity to superconductors is presented, especially paying attention to the band structure. We derive the general formula to calculate the free energy of the superconductor-graphite film-superconductor junction, which enable us to calculate the critical current of the junction. We introduce two models for the band structures: (1) Fermi point type (characteristic to monolayer case) and (2) zero-gap semiconductor type (characteristic to bilayer case). Then we calculate the superconducting critical current as a function of junction length and temperature.

  10. Study on band gap structure of Fibonacci quantum superlattices by using the transfer matrix method

    Science.gov (United States)

    Ferrando, V.; Castro-Palacio, J. C.; Marí, B.; Monsoriu, J. A.

    2014-02-01

    The scattering properties of particles in a one-dimensional Fibonacci sequence based potential have been analyzed by means of the Transfer Matrix Method. The electronic band gaps are examined comparatively with those obtained using the corresponding periodic potentials. The reflection coefficient shows self-similar properties for the Fibonacci superlattices. Moreover, by using the generalized Bragg's condition, the band gaps positions are derived from the golden mean involved in the design of the superlattice structure.

  11. Dual-Band Perfect Absorption by Breaking the Symmetry of Metamaterial Structure

    Science.gov (United States)

    Hai, Le Dinh; Qui, Vu Dinh; Dinh, Tiep Hong; Hai, Pham; Giang, Trinh Thị; Cuong, Tran Manh; Tung, Bui Son; Lam, Vu Dinh

    2017-02-01

    Since the first proposal of Landy et al. (Phys Rev Lett 100:207402, 2008), the metamaterial perfect absorber (MPA) has rapidly become one of the most crucial research trends. Recently, dual-band, multi-band and broadband MPA have been highly desirable in electronic applications. In this paper, we demonstrate and evaluate a MPA structure which can generate dual-band absorption operating at the microwave frequency by breaking the symmetry of structure. There is an agreement between simulation and experimental results. The results can be explained by using the equivalent LC circuit and the electric field distribution of this structure. In addition, various structures with different symmetry configurations were studied to gain greater insight into the absorption.

  12. Coexisting Honeycomb and Kagome Characteristics in the Electronic Band Structure of Molecular Graphene.

    Science.gov (United States)

    Paavilainen, Sami; Ropo, Matti; Nieminen, Jouko; Akola, Jaakko; Räsänen, Esa

    2016-06-08

    We uncover the electronic structure of molecular graphene produced by adsorbed CO molecules on a copper (111) surface by means of first-principles calculations. Our results show that the band structure is fundamentally different from that of conventional graphene, and the unique features of the electronic states arise from coexisting honeycomb and Kagome symmetries. Furthermore, the Dirac cone does not appear at the K-point but at the Γ-point in the reciprocal space and is accompanied by a third, almost flat band. Calculations of the surface structure with Kekulé distortion show a gap opening at the Dirac point in agreement with experiments. Simple tight-binding models are used to support the first-principles results and to explain the physical characteristics behind the electronic band structures.

  13. Upper critical field of KFe2As2 under pressure: A test for the change in the superconducting gap structure

    Energy Technology Data Exchange (ETDEWEB)

    Taufour, Valentin [Ames Laboratory; Foroozani, Neda [Washington University; Tanatar, Makariy A. [Ames Laboratory; Lim, Jinhyuk [Washington University; Kaluarachchi, Udhara [Iowa State University; Kim, Stella K. [Ames Laboratory; Liu, Yong [Ames Laboratory; Lograsso, Thomas A. [Ames Laboratory; Kogan, Vladimir G. [Ames Laboratory; Prozorov, Ruslan [Ames Laboratory; Bud' ko, Sergey L. [Ames Laboratory; Schilling, James S. [Washington University; Canfield, Paul C. [Ames Laboratory

    2014-06-01

    We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p*~1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p* up to 7.1 GPa. The T-p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p*, a change in the behavior of the upper critical field is revealed through a scaling analysis of the slope of Hc2 with the effective mass as determined from the A coefficient of the T2 term of the temperature-dependent resistivity. We show that this scaling provides a quantitative test for the changes of the superconducting gap structure and suggests the development of a kz modulation of the superconducting gap above p* as a most likely explanation.

  14. Low band gap frequencies and multiplexing properties in 1D and 2D mass spring structures

    Science.gov (United States)

    Aly, Arafa H.; Mehaney, Ahmed

    2016-11-01

    This study reports on the propagation of elastic waves in 1D and 2D mass spring structures. An analytical and computation model is presented for the 1D and 2D mass spring systems with different examples. An enhancement in the band gap values was obtained by modeling the structures to obtain low frequency band gaps at small dimensions. Additionally, the evolution of the band gap as a function of mass value is discussed. Special attention is devoted to the local resonance property in frequency ranges within the gaps in the band structure for the corresponding infinite periodic lattice in the 1D and 2D mass spring system. A linear defect formed of a row of specific masses produces an elastic waveguide that transmits at the narrow pass band frequency. The frequency of the waveguides can be selected by adjusting the mass and stiffness coefficients of the materials constituting the waveguide. Moreover, we pay more attention to analyze the wave multiplexer and DE-multiplexer in the 2D mass spring system. We show that two of these tunable waveguides with alternating materials can be employed to filter and separate specific frequencies from a broad band input signal. The presented simulation data is validated through comparison with the published research, and can be extended in the development of resonators and MEMS verification.

  15. Photonic Band Gap Structures with Periodically Arranged Atoms in a Two-Dimensional Photonic Crystal

    Institute of Scientific and Technical Information of China (English)

    LI Zhi-Yu; CHEN Fang; ZHOU Jian-Ying

    2005-01-01

    @@ Linear transmission, reflection and absorption spectra for a new two-dimensional photonic crystal with periodically arranged resonant atoms are examined. Numerical results show that a twin-gap structure with forbidden bands displaced from a non-doped bandgap structure can be produced as a result of atomic polarization. The absorption spectrum is also significantly altered compared to the single atom entity.

  16. Effects of weak nonlinearity on dispersion relations and frequency band-gaps of periodic structures

    DEFF Research Database (Denmark)

    Sorokin, Vladislav; Thomsen, Jon Juel

    2015-01-01

    The analysis of the behaviour of linear periodic structures can be traced back over 300 years, to Sir Isaac Newton, and still attracts much attention. An essential feature of periodic struc-tures is the presence of frequency band-gaps, i.e. frequency ranges in which waves cannot propagate...

  17. Phononic band gaps and vibrations in one- and two-dimensional mass-spring structures

    DEFF Research Database (Denmark)

    Jensen, Jakob Søndergaard

    2003-01-01

    The vibrational response of finite periodic lattice structures subjected to periodic loading is investigated. Special attention is devoted to the response in frequency ranges with gaps in the band structure for the corresponding infinite periodic lattice. The effects of boundaries, viscous dampin...

  18. Magnetic shielding performance of superconducting YBCO thin film in a multilayer device structure

    Energy Technology Data Exchange (ETDEWEB)

    Uzun, Y., E-mail: uzunyigitcan@gmail.com; Avci, I.

    2014-12-15

    Highlights: • A multilayer structure was fabricated in the form of YBCO/STO/YBCO. • Bottom layer was used as a magnetic shield. • The top layer was patterned as a microbridge. • Magnetic shielding performance of the bottom layer onto the microbridge was tested. • I{sub c} of the microbridge was kept constant under the various magnetic fields. - Abstract: Magnetic shielding performance of superconducting YBaCu{sub 2}O{sub 7−x} (YBCO) thin film on an YBCO microbridge was analyzed in a multilayer structure. A sandwich type multilayer structure was fabricated onto a single crystal (1 0 0) SrTiO{sub 3} (STO) substrate in the form of YBCO/STO/YBCO by depositing a thin STO interlayer in between two YBCO layers. The top YBCO was patterned as 20 μm width meander-type microbridges and the bottom layer YBCO was used as magnetic shield. YBCO and STO thin films were deposited by dc and rf magnetron sputtering respectively, and the patterning was performed by using standard photolithography and wet etching. In order to enhance long-term stability of the final device, an additional STO thin film was deposited onto the device as an encapsulation layer. Electrical and magnetic characterizations of the YBCO thin film layers were carried out by means of ac magnetic susceptibility (χ–T) and resistance vs. temperature (R–T) measurements. The current–voltage (I–V) measurements were performed on the microbridges at 77 K by observing the shielding performance of the bottom YBCO layer under various applied magnetic fields. The results were compared with that of a same-type single layer YBCO device without a shielding layer. The zero field critical current value of the single layer 20 μm wide YBCO device was measured as 30 mA and decreased down to 20 mA as the field increased up to 100 mT. The same measurements on the multilayer device showed that the critical current values remained almost constant around 27 mA as the applied field increased.

  19. Influence of calcium on transport properties, band spectrum and superconductivity of YBa{sub 2}Cu{sub 3}O{sub y} and YBa{sub 1.5}La{sub 0.5}Cu{sub 3}O{sub y}{sup {center_dot}}

    Energy Technology Data Exchange (ETDEWEB)

    Gasumyants, V.E.; Vladimirskaya, E.V. [State Technical Univ., St. Petersburg (Russian Federation); Patrina, I.B. [Institute of Silicate Chemistry, St. Petersburg (Russian Federation)

    1994-12-31

    The comparative investigation of transport phenomena in Y{sub 1-x}Ca{sub x}Ba{sub 2}Cu{sub 3}O{sub y} (0y>6.87 and 6.73y>6.96) and YBa{sub 2-x}La{sub x}Cu{sub 3}O{sub y} (0band. The main parameters of the band spectrum (the band filling with electrons degree and the total effective band width) have been determined. The dependencies of these ones from contents of substituting elements are discussed. Analyzing the results obtained simultaneously with the tendencies in oxygen content and critical temperature change we have confirmed the conclusion that the oxygen sublattice disordering has a determinant effect on band structure parameters and superconductive properties of YBa{sub 2}Cu{sub 3}O{sub y}{sup {center_dot}}. The results obtained suggest that Ca gives rise to some peculiarities in band spectrum of this compound.

  20. Electronic band structure of a type-Ⅱ 'W' quantum well calculated by an eight-band k·p model

    Institute of Scientific and Technical Information of China (English)

    Yu Xiu; Gu Yong-Xian; Wang Qing; Wei Xin; Chen Liang-Hui

    2011-01-01

    In this paper, we present an investigation of type-Ⅱ 'W' quantum wells for the InAs/Ga1-xInxSb/AlSb family, where 'W' denotes the conduction profile of the material. We focus our attention on using the eight-band k·p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period-AlSb/InAs/Ga1-xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1-xInxSb layer and the alloy composition in Ga1-xInxSb separately. In the last part, in order to compare the eight-band k·p model, we recalculate the conduction bands of the 'W' structure using the one-band k·p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained.

  1. Superconducting transistor

    Science.gov (United States)

    Gray, Kenneth E.

    1979-01-01

    A superconducting transistor is formed by disposing three thin films of superconducting material in a planar parallel arrangement and insulating the films from each other by layers of insulating oxides to form two tunnel junctions. One junction is biased above twice the superconducting energy gap and the other is biased at less than twice the superconducting energy gap. Injection of quasiparticles into the center film by one junction provides a current gain in the second junction.

  2. Development of a superconducting CH-accelerator-structure for light and heavy ions; Entwicklung einer supraleitenden CH-Beschleuniger-Struktur fuer leichte und schwere Ionen

    Energy Technology Data Exchange (ETDEWEB)

    Liebermann, Holger

    2007-07-01

    This work deals with the development of the prototype of a superconducting CH accelerator structure. The simulations were calculated with the program CST Microwave Studio. It is based on the finite integration theory, which the Maxwell equations in a two-grid matrix form convicted so they can be solved numerically. In another chapter, a method for determining the coupling strength is discussed. The conditions that previously were created for the optimization of the prototype of the superconducting CH structure are described. It was for the optimization of the field distribution on the beam axis by adjusting the end cell design, optimization of support for the magnetic and electric fields, leading to reduction of the quadrupole component of the CH-structure, the coupling and, finally, the possibility of static tuning during the completion of the structure. On the basis of these investigations the completion of an initial prototype superconducting at the company ACCEL in Bergisch Gladbach was commissioned. Finally simulations for an operation accelerator facility, and a look at possible areas of the superconducting CH-structure are presented. The optimizations performed for the high power injector led to a more stable operation of the plant. Through this work it could be shown that the newly-CH structure is very well suited for use in superconducting accelerators. (orig.)

  3. UWB Band-notched Adjustable Antenna Using Concentric Split-ring Slots Structure

    Science.gov (United States)

    Yin, Y.; Hong, J. S.

    2014-09-01

    In this paper, a kind of concentric split-ring slots structure is utilized to design a novel triple-band-notched UWB antenna. Firstly, a concentric split-ring slots structure that has a higher VSWR than that of a single slot at notch frequency is presented. What's more, the structure is very simple and feasible to obtain notched-band at different frequency by adjustment of the length of slot. Secondly, a triple-band-notched antenna, whose notched bands are at 3.52-3.81 GHz for WiMAX and 5.03-5.42 GHz and 5.73-56.17 GHz for WLAN, is designed by using this structure. At last, a compact size of 24 × 30 mm2 of the proposed antenna has been fabricated and measured and it is shown that the proposed antenna has a broadband matched impedance (3.05-14 GHz, VSWR < 2), relatively stable gain and good omnidirectional radiation patterns at low bands.

  4. Band structure of fcc-C60 solid state crystal study

    Directory of Open Access Journals (Sweden)

    S Javanbakht

    2009-09-01

    Full Text Available We studied the architecture of the C60 cluster to drive its atomic positions which can be seen at room temperature. We then used the obtained carbon positions as a basis set for the fcc structure to construct the fcc-C60 compound. Self consistent calculations were performed based on the density functional theory (DFT utilizing the accurate WIEN2K code to solve the single-particle Kohen-Sham equation within the augmented plane waves plus local orbital (APW+lo method. The cohesive energy has been found to be 1.537 eV for the fcc-C60 . The calculated small cohesive energy that results from the weak Van der Waals-London interactions among a C60 cluster with its nearest neighbors is in good agreement with experiment. The electron densities of states (DOSs were calculated for a C60 macromolecule as well as the fcc-C60 compound and the results were compared with each other. The band gap from DOS calculations has been found to be 0.7 eV. Band structures were also calculated within the generalized gradient approximation (GGA. The band structure calculation results in 1.04 eV for the direct band gap. Two kinds of σ and π bonds were determined in the band structure. Our results are in good agreement with experiment and pseudopotential calculations.

  5. Superconductivity in MgB2: clean or dirty?

    Science.gov (United States)

    Mazin, I I; Andersen, O K; Jepsen, O; Dolgov, O V; Kortus, J; Golubov, A A; Kuz'menko, A B; Van Der Marel, D

    2002-09-01

    A large number of experimental facts and theoretical arguments favor a two-gap model for superconductivity in MgB2. However, this model predicts strong suppression of the critical temperature by interband impurity scattering and, presumably, a strong correlation between the critical temperature and the residual resistivity. No such correlation has been observed. We argue that this fact can be understood if the band disparity of the electronic structure is taken into account, not only in the superconducting state, but also in normal transport.

  6. Graphene Oxide Regulated Tin Oxide Nanostructures: Engineering Composition, Morphology, Band Structure, and Photocatalytic Properties.

    Science.gov (United States)

    Pan, Xiaoyang; Yi, Zhiguo

    2015-12-16

    A facile, one-step hydrothermal method has been developed to fabricate tin oxide-reduced graphene oxide (Sn-RGO) nanocomposites with tunable composition, morphology, and energy band structure by utilizing graphene oxide (GO) as a multifunctional two-dimensional scaffold. By adjusting the GO concentration during synthesis, a variety of tin oxide nanomaterials with diverse composition and morphology are obtained. Simultaneously, the varying of GO concentration can also narrow the bandgap and tune the band edge positions of the Sn-RGO nanocomposites. As a result, the Sn-RGO nanocomposites with controllable composition, morphology, and energy band structure are obtained, which exhibit efficient photoactivities toward methyl orange (MO) degradation under visible-light irradiation. It is expected that our work would point to the new possibility of using GO for directing synthesis of semiconductor nanomaterials with tailored structure and physicochemical properties.

  7. Ab initio theory for ultrafast magnetization dynamics with a dynamic band structure

    Science.gov (United States)

    Mueller, B. Y.; Haag, M.; Fähnle, M.

    2016-09-01

    Laser-induced modifications of magnetic materials on very small spatial dimensions and ultrashort timescales are a promising field for novel storage and spintronic devices. Therefore, the contribution of electron-electron spin-flip scattering to the ultrafast demagnetization of ferromagnets after an ultrashort laser excitation is investigated. In this work, the dynamical change of the band structure resulting from the change of the magnetization in time is taken into account on an ab initio level. We find a large influence of the dynamical band structure on the magnetization dynamics and we illustrate the thermalization and relaxation process after laser irradiation. Treating the dynamical band structure yields a demagnetization comparable to the experimental one.

  8. Superconductive articles including cerium oxide layer

    Science.gov (United States)

    Wu, Xin D.; Muenchausen, Ross E.

    1993-01-01

    A ceramic superconductor comprising a metal oxide substrate, a ceramic high temperature superconductive material, and a intermediate layer of a material having a cubic crystal structure, said layer situated between the substrate and the superconductive material is provided, and a structure for supporting a ceramic superconducting material is provided, said structure comprising a metal oxide substrate, and a layer situated over the surface of the substrate to substantially inhibit interdiffusion between the substrate and a ceramic superconducting material deposited upon said structure.

  9. Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices

    DEFF Research Database (Denmark)

    Gorczyca, I.; Suski, T.; Christensen, Niels Egede;

    2012-01-01

    for the gap error. The calculated band gap shows a strong decrease with the thickness (m) of the InN well. In superlattices containing a single layer of InN (m = 1) the band gap increases weakly with the GaN barrier thickness n, reaching a saturation value around 2 eV. In superlattices with n = m and n > 5......InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/GaN......(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ≥ m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction...

  10. Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

    Energy Technology Data Exchange (ETDEWEB)

    Peterman, D.J.

    1980-01-01

    Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH/sub 2/ and YH/sub 2/ were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH/sub 2/ cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 < x < 2.9 are presented which, as expected, indicate a more premature occupation of the octahedral sites in the larger LaH/sub 2/ lattice. These experimental results also suggest that, in contrast to recent calculations, LaH/sub 3/ is a small-band-gap semiconductor.

  11. Cherenkov oscillator operating at the second band gap of leakage waveguide structures

    Science.gov (United States)

    Jang, Kyu-Ha; Park, Seong Hee; Lee, Kitae; Jeong, Young Uk

    2016-10-01

    An electromagnetic wave source operating around second band gaps of metallic grating structures is presented. The considered metallic grating structures are not perfect periodic but inhomogeneously structured within a period to have a second band gap where the wavelength is equal to the period of the structures. The radiation mechanism by an electron beam in the structures is different from the well-known Smith-Purcell radiation occurring in perfect periodic grating structures. That is, the radiating wave has a single frequency and the radiation is unidirectional. When the energy of the electron beam is synchronized at the standing wave point in the dispersion curves, strong interaction happens and coherent radiation perpendicular to the grating surface is generated with relatively lower starting oscillation current.

  12. Cherenkov oscillator operating at the second band gap of leakage waveguide structures

    Directory of Open Access Journals (Sweden)

    Kyu-Ha Jang

    2016-10-01

    Full Text Available An electromagnetic wave source operating around second band gaps of metallic grating structures is presented. The considered metallic grating structures are not perfect periodic but inhomogeneously structured within a period to have a second band gap where the wavelength is equal to the period of the structures. The radiation mechanism by an electron beam in the structures is different from the well-known Smith-Purcell radiation occurring in perfect periodic grating structures. That is, the radiating wave has a single frequency and the radiation is unidirectional. When the energy of the electron beam is synchronized at the standing wave point in the dispersion curves, strong interaction happens and coherent radiation perpendicular to the grating surface is generated with relatively lower starting oscillation current.

  13. First-principles study of the electronic structure of iron-selenium: Implications for electron-phonon superconductivity

    Science.gov (United States)

    Koufos, Alexander P.; Papaconstantopoulos, Dimitrios A.; Mehl, Michael J.

    2014-01-01

    We have performed density functional theory calculations using the linearized augmented plane wave method (LAPW) with the local density approximation (LDA) functional to study the electronic structure of the iron-based superconductor iron-selenium (FeSe). In our study, we have performed a comprehensive set of calculations involving structural, atomic, and spin configurations. All calculations were executed using the tetragonal lead-oxide or P4/nmm structure, with various volumes, c /a ratios, and internal parameters. Furthermore, we investigated the spin polarization using the LDA functional to assess ferromagnetism in this material. The paramagnetic LDA calculations find the equilibrium configuration of FeSe in the P4/nmm structure to have a volume of 472.5 a.u.3 with a c /a ratio of 1.50 and internal parameter of 0.255, with the ferromagnetic having comparable results to the paramagnetic case. In addition, we calculated total energies for FeSe using a pseudopotential method, and found comparable results to the LAPW calculations. Superconductivity calculations were done using the Gaspari-Gyorffy and the McMillan formalisms and found substantial electron-phonon coupling. Under pressure, our calculations show that the superconductivity critical temperature continues to rise, but underestimates the measured values.

  14. Structural studies of Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$ $+$ Ag superconducting system

    Indian Academy of Sciences (India)

    N RADHIKESH RAVEENDRAN; A K SINHA; R RAJARAMAN; M PREMILA; E P AMALADASS; K VINOD; J JANAKI; S KALAVATHI; AWADHESH MANI

    2016-06-01

    We have studied for the first time the effect of Ag addition (0–15 wt%) to the superconducting system, Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$, on its crystal structure and local structural features, using synchrotron X-ray diffraction(SXRD) and Raman spectroscopy, respectively. SXRD and subsequent Rietveld refinement studies on powders of Nd$_{1.85}$Ce$_{0.15}$CuO$_4$ $+$ Ag system indicate a small but significant change in lattice parameter upon Ag addition, showing evidence for possible incorporation of Ag to the extent of $\\sim$1 wt%. Raman spectroscopic studies indicate that the parent structure of Nd$_{1.85}$Ce$_{0.15}CuO$_{4}$ remains unaffected with no major local structural changes on doping with silver. However, all Raman modes show minor phonon hardening upon Ag addition, which is consistent with the unit cell volume reduction as is observed in XRD. A systematic bleaching out of the apical oxygen defect mode was also observed with increased Ag addition. Polarized Raman measurements helped to identify the asymmetric nature of the B1g Raman mode. X-ray diffraction studies on pellets of Nd$_{1.85}$Ce$_{0.15}CuO$_4$ $+$ Ag system further indicate a randomization of preferred orientation upon Ag addition. The superconductivity of the Nd$_{1.85}$Ce$_{0.15}$CuO$_4$ $+$ Ag system has been well characterized for all the compositions studied.

  15. Multi-quasiparticle {gamma}-band structure in neutron-deficient Ce and Nd isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Sheikh, J.A. [Physics Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831 (United States); Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Bhat, G.H. [Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Palit, R.; Naik, Z. [Tata Institute of Fundamental Research, Colaba, Mumbai, 400 005 (India); Sun, Y. [Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)], E-mail: sunyang@sjtu.edu.cn

    2009-06-01

    The newly developed multi-quasiparticle triaxial projected shell model approach is employed to study the high-spin band structures in neutron-deficient even-even Ce- and Nd-isotopes. It is observed that {gamma}-bands are built on each intrinsic configuration of the triaxial mean-field deformation. Due to the fact that a triaxial configuration is a superposition of several K-states, the projection from these states results in several low-lying bands originating from the same intrinsic configuration. This generalizes the well-known concept of the surface {gamma}-oscillation in deformed nuclei based on the ground-state to {gamma}-bands built on multi-quasiparticle configurations. This new feature provides an alternative explanation on the observation of two I=10 aligning states in {sup 134}Ce and both exhibiting a neutron character.

  16. Multi-Quasiparticle Gamma-Band Structure in Neutron-Deficient Ce and Nd Isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Sheikh, Javid [ORNL; Bhat, G. H. [University of Kashmir, Srinagar, India; Palit, R. [Tata Institute of Fundamental Research, Mumbai, India; Naik, Z. [Tata Institute of Fundamental Research, Mumbai, India; Sun, Y. [Shanghai Jiao Tong University, Shanghai

    2009-01-01

    The newly developed multi-quasiparticle triaxial projected shell-model approach is employed to study the high-spin band structures in neutron-deficient even-even Ce and Nd isotopes. It is observed that gamma bands are built on each intrinsic configuration of the triaxial mean-field deformation. Due to the fact that a triaxial configuration is a superposition of several K states, the projection from these states results in several low-lying bands originating from the same intrinsic configuration. This generalizes the well-known concept of the surface gamma oscillation in deformed nuclei based on the ground state to gamma bands built on multi-quasiparticle configurations. This new feature provides an alternative explanation on the observation of two I=10 aligning states in ^{134}Ce and both exhibiting a neutron character.

  17. TUNABLE Band Structures of 2d Multi-Atom Archimedean-Like Phononic Crystals

    Science.gov (United States)

    Xu, Y. L.; Chen, C. Q.; Tian, X. G.

    2012-06-01

    Two dimensional multi-atom Archimedean-like phononic crystals (MAPCs) can be obtained by adding "atoms" at suitable positions in primitive cells of traditional simple lattices. Band structures of solid-solid and solid-air MAPCs are computed by the finite element method in conjunction with the Bloch theory. For the solid-solid system, our results show that the MAPCs can be suitably designed to split and shift band gaps of the corresponding traditional simple phononic crystal (i.e., with only one scatterer inside a primitive cell). For the solid-air system, the MAPCs have more and wider band gaps than the corresponding traditional simple phononic crystal. Numerical calculations for both solid-solid and solid-air MAPCs show that the band gap of traditional simple phononic crystal can be tuned by appropriately adding "atoms" into its primitive cell.

  18. Valence band structure of strained Si/(111)Si1-xGex

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The strained Si techique has been widely adopted in the high-speed and high-performance devices and circuits. Based on the valence band E-k relations of strained Si/(111)Si1-xGex, the valence band and hole effective mass along the [111] and [-110] directions were obtained in this work. In comparison with the relaxed Si, the valence band edge degeneracy was partially lifted, and the significant change was observed band structures along the [111] and [-110] directions, as well as in its corresponding hole effective masses with the increasing Ge fraction. The results obtained can provide valuable references to the investigation concerning the Si-based strained devices enhancement and the conduction channel design related to stress and orientation.

  19. Crystal structure and band gap of AlGaAsN

    Science.gov (United States)

    Munich, D. P.; Pierret, R. F.

    1987-09-01

    Quantum dielectric theory is applied to the quaternary alloy Al xGa 1- xAs 1- yN y to predict its electronic properties as a function of Al and N mole fractions. Results are presented for the expected crystal structure, minimum electron energy band gap, and direction in k-space of the band gap minimum for all x and y values. The results suggest that, for a proper choice of x and y, Al xGa 1- xAs 1- yN y could exhibit certain advantages over Al xGa 1- xAs when utilized in field-effect transistor structures.

  20. Quantum Devices Based on Modern Band Structure Engineering and Epitaxial Technology

    Science.gov (United States)

    Razeghi, Manijeh

    Modern band structure engineering is based both on the important discoveries of the past century and modern epitaxial technology. The general goal is to control the behavior of charge carriers on an atomic scale, which affects how they interact with each other and their environment. Starting from the basic semiconductor heterostructure, band structure engineering has evolved into a powerful discipline, employing lower dimensionality to demonstrate new material properties. Several modern technologies under development are used as examples of how this discipline is enabling new types of devices and new functionality in areas with immediate application.

  1. Superconductivity in carbon nanomaterials

    Science.gov (United States)

    Dlugon, Katarzyna

    The purpose of this thesis is to explain the phenomenon of superconductivity in carbon nanomaterials such as graphene, fullerenes and carbon nanotubes. In the introductory chapter, there is a description of superconductivity and how it occurs at critical temperature (Tc) that is characteristic and different to every superconducting material. The discovery of superconductivity in mercury in 1911 by Dutch physicist Heike Kamerlingh Onnes is also mentioned. Different types of superconductors, type I and type II, low and high temperatures superconductors, as well as the BCS theory that was developed in 1957 by Bardeen, Cooper, and Schrieffer, are also described in detail. The BCS theory explains how Cooper's pairs are formed and how they are responsible for the superconducting properties of many materials. The following chapters explain superconductivity in doped fullerenes, graphene and carbon nanotubes, respectively. There is a thorough explanation followed by many examples of different types of carbon nanomaterials in which small changes in chemical structure cause significant changes in superconducting properties. The goal of this research was not only to take into consideration well known carbon based superconductors but also to search for the newest available materials such as the fullerene nanowhiskers discovered quite recently. There is also a presentation of fairly new ideas about inducing superconductivity in a monolayer of graphene which is more challenging than inducing superconductivity in graphite by simply intercalating metal atoms between its graphene sheets. An effort has been taken to look for any available information about carbon nanomaterials that have the potential to superconduct at room temperature, mainly because discovery of such materials would be a real revolution in the modern world, although no such materials have been discovered yet.

  2. Band Structure Simulations of the Photoinduced Changes in the MgB2:Cr Films

    Directory of Open Access Journals (Sweden)

    Iwan V. Kityk

    2015-04-01

    Full Text Available An approach for description of the photoinduced nonlinear optical effects in the superconducting MgB2:Cr2O3 nanocrystalline film is proposed. It includes the molecular dynamics step-by-step optimization of the two separate crystalline phases. The principal role for the photoinduced nonlinear optical properties plays nanointerface between the two phases. The first modified layers possess a form of slightly modified perfect crystalline structure. The next layer is added to the perfect crystalline structure and the iteration procedure is repeated for the next layer. The total energy here is considered as a varied parameter. To avoid potential jumps on the borders we have carried out additional derivative procedure.

  3. Edge geometry superconducting tunnel junctions utilizing an NbN/MgO/NbN thin film structure

    Science.gov (United States)

    Hunt, Brian D. (Inventor); Leduc, Henry G. (Inventor)

    1992-01-01

    An edge defined geometry is used to produce very small area tunnel junctions in a structure with niobium nitride superconducting electrodes and a magnesium oxide tunnel barrier. The incorporation of an MgO tunnel barrier with two NbN electrodes results in improved current-voltage characteristics, and may lead to better junction noise characteristics. The NbN electrodes are preferably sputter-deposited, with the first NbN electrode deposited on an insulating substrate maintained at about 250 C to 500 C for improved quality of the electrode.

  4. Relation of Structure and Superconductivity in Self-Compensating Y1-xCaxBa2-xLaxCu3Oy

    Institute of Scientific and Technical Information of China (English)

    SUN Xue-Feng; YU Jing; WANG Fa; ZHANG Han

    2006-01-01

    @@ The self-compensating compound of Y1-xCaxBa2-xLaxCu3Oy is synthesized through a solid-state reaction method with x from 0.25 to 0.55. Structural and superconducting properties have been investigated by x-ray diffraction, Rietveld refinement, and dc magnetization measurement, respectively. The impure peaks appear when x is more than 0.5 in the diffraction pattern. Orthorhombic-tetragonal transition occurs at x=0.45.Some local structural parameters, such as Cu(1)-O(4), Cu(2)-O(4) bond lengths, change randomly in a narrow range. The relationship between the character of (Ba/La)-O plane and Tc is rather interesting. We attribute the behaviour of superconductivity to the joint effects of these local structural parameters. The results give the evidence that the influence of the structural change on superconductivity is essential and independent of carrier concentration.

  5. Complete multipactor suppression in an X-band dielectric-loaded accelerating structure

    Energy Technology Data Exchange (ETDEWEB)

    Jing, C. [Euclid Techlabs, LLC, 5900 Harper Rd, Solon, Ohio 44139, USA; High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Gold, S. H. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375, USA; Fischer, Richard [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375, USA; Gai, W. [High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

    2016-05-09

    Multipactor is a major issue limiting the gradient of rf-driven Dielectric-Loaded Accelerating (DLA) structures. Theoretical models have predicted that an axial magnetic field applied to DLA structures may completely block the multipactor discharge. However, previous attempts to demonstrate this magnetic field effect in an X-band traveling-wave DLA structure were inconclusive, due to the axial variation of the applied magnetic field, and showed only partial suppression of the multipactor loading [Jing et al., Appl. Phys. Lett. 103, 213503 (2013)]. The present experiment has been performed under improved conditions with a uniform axial magnetic field extending along the length of an X-band standing-wave DLA structure. Multipactor loading began to be continuously reduced starting from 3.5 kG applied magnetic field and was completely suppressed at 8 kG. Dependence of multipactor suppression on the rf gradient inside the DLA structure was also measured.

  6. Band gap structures in two-dimensional super porous phononic crystals.

    Science.gov (United States)

    Liu, Ying; Sun, Xiu-zhan; Chen, Shao-ting

    2013-02-01

    As one kind of new linear cellular alloys (LCAs), Kagome honeycombs, which are constituted by triangular and hexagonal cells, attract great attention due to the excellent performance compared to the ordinary ones. Instead of mechanical investigation, the in-plane elastic wave dispersion in Kagome structures are analyzed in this paper aiming to the multi-functional application of the materials. Firstly, the band structures in the common two-dimensional (2D) porous phononic structures (triangular or hexagonal honeycombs) are discussed. Then, based on these results, the wave dispersion in Kagome honeycombs is given. Through the component cell porosity controlling, the effects of component cells on the whole responses of the structures are investigated. The intrinsic relation between the component cell porosity and the critical porosity of Kagome honeycombs is established. These results will provide an important guidance in the band structure design of super porous phononic crystals.

  7. The crystal structure of superconducting FeSe{sub 1-x}Te{sub x} by pulsed neutron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Lehman, M C; Llobet, A; Horigane, K; Louca, D, E-mail: mcl4v@virginia.edu

    2010-11-01

    A transition to a superconducting state was recently observed in the binary alloy of FeSe{sub 1-x}Te{sub x} system where TC rises with increasing x. The substitution of the larger Te for Se ion results in no additional charges but increases the internal chemical pressure. Earlier studies suggested that the crystal structure maintains the tetragonal P4/nmm symmetry with the substitution of Te where the average bond angle, {alpha}, decreases considerably from {approx} 104{sup 0} in FeSe to 100.5{sup 0} in the mixed phase of FeSe{sub 0.5}Te{sub 0.5}. With the use of pulsed neutron power diffraction and the Rietveld analysis, the crystal structure refinement for FeSe{sub 0.5}Te{sub 0.5} yielded very large thermal factors in the superconducting phase indicative of the presence of structural distortions that may be significant in understanding the electronic and magnetic properties of this system.

  8. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, Kevin Jerome [Iowa State Univ., Ames, IA (United States)

    2001-01-01

    Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.

  9. Study on temperature property of band structures in onedimensional photonic crystals

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Using transfer matrix method, the optical transmission properties in one-dimensional (1-D) photonic crystal is analyzed.When the temperature varies, not only the refractive index of the optical medium is changed because of the thermo-optical effect, but also the thickness of the optical medium is changed due to the thermal-expansion effect. Thus, the structure of 1/4 wave-plate stack in original photonic crystal is destroyed and the band structure varies. In this work, the effects of the temperature variation on the first and second band gap in a 1-D photonic crystal are analyzed in detail. It is found that the changes of the starting wavelength, the cut-off wavelength and the forbidden band width depend linearly on the temperature.

  10. Global Evolutionary Algorithms in the Design of Electromagnetic Band Gap Structures with Suppressed Surface Waves Propagation

    Directory of Open Access Journals (Sweden)

    P. Kovacs

    2010-04-01

    Full Text Available The paper is focused on the automated design and optimization of electromagnetic band gap structures suppressing the propagation of surface waves. For the optimization, we use different global evolutionary algorithms like the genetic algorithm with the single-point crossover (GAs and the multi-point (GAm one, the differential evolution (DE and particle swarm optimization (PSO. The algorithms are mutually compared in terms of convergence velocity and accuracy. The developed technique is universal (applicable for any unit cell geometry. The method is based on the dispersion diagram calculation in CST Microwave Studio (CST MWS and optimization in Matlab. A design example of a mushroom structure with simultaneous electromagnetic band gap properties (EBG and the artificial magnetic conductor ones (AMC in the required frequency band is presented.

  11. New band structures and an unpaired crossing in {sup 78}Kr

    Energy Technology Data Exchange (ETDEWEB)

    Sun, H.; Doring, J.; Johns, R.A.; Solomon, G.; Tabor, S.; Devlin, M.; LaFosse, D.; Lerma, F.; Sarantites, D.; Baktash, C.; Rudolph, D.; Yu, C.H.; Lee, I.Y.; Macchiavelli, A.; Birriel, I.; Saladin, J.; Winchell, D.; Wood, V.Q.; Ragnarsson, I.

    1998-07-06

    High-spin states in {sup 78}Kr were studied using the {sup 58}Ni({sup 23}Na,3p) reaction at 70 MeV and the {sup 58}Ni({sup 28}Si,{alpha}4p) reaction at 130 MeV. Prompt {gamma}-{gamma} coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24{sup +} state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands.

  12. New band structures and an unpaired crossing in {sup 78}Kr

    Energy Technology Data Exchange (ETDEWEB)

    Sun, H.; Doering, J.; Johns, G.D.; Kaye, R.A.; Solomon, G.Z.; Tabor, S.L. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Doering, J. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Devlin, M.; LaFosse, D.R.; Lerma, F.; Sarantites, D.G. [Department of Chemistry, Washington University, St. Louis, Missouri 63130 (United States); Baktash, C.; Rudolph, D.; Yu, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Lee, I.Y.; Macchiavelli, A.O. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Birriel, I.; Saladin, J.X.; Winchell, D.F.; Wood, V.Q. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Ragnarsson, I. [Department of Mathematical Physics, Lund Institute of Technology, S-22100 Lund (Sweden)

    1999-02-01

    High-spin states in {sup 78}Kr were studied using the {sup 58}Ni({sup 23}Na,3p) reaction at 70 MeV and the {sup 58}Ni({sup 28}Si,{alpha}4p) reaction at 130 MeV. Prompt {gamma}-{gamma} coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24{sup +} state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. {copyright} {ital 1999} {ital The American Physical Society}

  13. Superconductivity in compensated and uncompensated semiconductors.

    Science.gov (United States)

    Yanase, Youichi; Yorozu, Naoyuki

    2008-12-01

    We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature Tc around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si.

  14. Superconductivity in compensated and uncompensated semiconductors

    Directory of Open Access Journals (Sweden)

    Youichi Yanase and Naoyuki Yorozu

    2008-01-01

    Full Text Available We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature Tc around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si.

  15. Automatically inferred Markov network models for classification of chromosomal band pattern structures.

    Science.gov (United States)

    Granum, E; Thomason, M G

    1990-01-01

    A structural pattern recognition approach to the analysis and classification of metaphase chromosome band patterns is presented. An operational method of representing band pattern profiles as sharp edged idealized profiles is outlined. These profiles are nonlinearly scaled to a few, but fixed number of "density" levels. Previous experience has shown that profiles of six levels are appropriate and that the differences between successive bands in these profiles are suitable for classification. String representations, which focuses on the sequences of transitions between local band pattern levels, are derived from such "difference profiles." A method of syntactic analysis of the band transition sequences by dynamic programming for optimal (maximal probability) string-to-network alignments is described. It develops automatic data-driven inference of band pattern models (Markov networks) per class, and uses these models for classification. The method does not use centromere information, but assumes the p-q-orientation of the band pattern profiles to be known a priori. It is experimentally established that the method can build Markov network models, which, when used for classification, show a recognition rate of about 92% on test data. The experiments used 200 samples (chromosome profiles) for each of the 22 autosome chromosome types and are designed to also investigate various classifier design problems. It is found that the use of a priori knowledge of Denver Group assignment only improved classification by 1 or 2%. A scheme for typewise normalization of the class relationship measures prove useful, partly through improvements on average results and partly through a more evenly distributed error pattern. The choice of reference of the p-q-orientation of the band patterns is found to be unimportant, and results of timing of the execution time of the analysis show that recent and efficient implementations can process one cell in less than 1 min on current standard

  16. Photonic Band Structure of Dispersive Metamaterials Formulated as a Hermitian Eigenvalue Problem

    KAUST Repository

    Raman, Aaswath

    2010-02-26

    We formulate the photonic band structure calculation of any lossless dispersive photonic crystal and optical metamaterial as a Hermitian eigenvalue problem. We further show that the eigenmodes of such lossless systems provide an orthonormal basis, which can be used to rigorously describe the behavior of lossy dispersive systems in general. © 2010 The American Physical Society.

  17. Carrier-carrier relaxation kinetics in quantum well semiconductor structures with nonparabolic energy bands

    DEFF Research Database (Denmark)

    Dery, H.; Tromborg, Bjarne; Eisenstein, G.

    2003-01-01

    We describe carrier-carrier scattering dynamics in an inverted quantum well structure including the nonparabolic nature of the valance band. A solution of the semiconductor Bloch equations yields strong evidence to a large change in the temporal evolution of the carrier distributions compared...

  18. Surface plasmon polariton band gap structures: implications to integrated plasmonic circuits

    DEFF Research Database (Denmark)

    Bozhevolnyi, S. I.; Volkov, V. S.; Østergaard, John Erland;

    2001-01-01

    Conventional photonic band gap (PBG) structures are composed of regions with periodic modulation of refractive index that do not allow the propagation of electromagnetic waves in a certain interval of wavelengths, i.e., that exhibit the PBG effect. The PBG effect is essentially an interference ph...

  19. Band structure of one-dimensional plasma photonic crystals using the Fresnel coefficients method

    Science.gov (United States)

    Jafari, A.; Rahmat, A.

    2016-11-01

    The current study has examined the band structures of two types of photonic crystals (PCs). The first is a one-dimensional metamaterial photonic crystal (1DMMPC) composed of double-layered units for which both layers of each unit are dielectric. The second type is a very similar one-dimensional plasma photonic crystal (1DPPC) also composed of double-layered units in which the first layer is a dielectric material but the second is a plasma layer. This study compares the band structures of the 1DMMPC with specific optical characteristics of the 1DPPC using the Fresnel coefficients method and also compares the results of this method with the results of the transfer matrix method. It is concluded that the dependency of the electric permittivity of the plasma layer on the incident field frequency causes differences in the band structures in 1DMMPC and 1DPPC for both TE and TM polarizations and their gaps reside in different frequencies. The band structures of the 1DMMPC and 1DPPC are confirmed by the results of the transfer matrix method.

  20. Evolution of structural relaxation spectra of glycerol within the gigahertz band

    Science.gov (United States)

    Franosch, T.; Göauttze, W.; Mayr, M. R.; Singh, A. P.

    1997-03-01

    The structural relaxation spectra and the crossover from relaxation to oscillation dynamics, as measured by Wuttke et al. [Phys. Rev. Lett. 72, 3052 (1994)] for glycerol within the GHz band by depolarized light scattering, are described by the solutions of a schematic mode coupling theory model. The applicability of scaling laws for the discussion of the model solutions is considered.

  1. Band structure and optical properties of LiKB4O7 single crystal

    NARCIS (Netherlands)

    Smok, P; Seinert, H; Kityk, [No Value; Berdowski, J

    2003-01-01

    The band structure (BS), electronic charge density distribution and linear optical properties of the LiKB4O7 (LKB4) single crystal are calculated using a self-consistent norm-conserving pseudo-potential method within the framework of the local density approximation theory. Dispersion of the imaginar

  2. Direct Measurement of the Band Structure of a Buried Two-Dimensional Electron Gas

    DEFF Research Database (Denmark)

    Miwa, Jill; Hofmann, Philip; Simmons, Michelle Y.;

    2013-01-01

    We directly measure the band structure of a buried two dimensional electron gas (2DEG) using angle resolved photoemission spectroscopy. The buried 2DEG forms 2 nm beneath the surface of p-type silicon, because of a dense delta-type layer of phosphorus n-type dopants which have been placed there. ...

  3. Band structure of thin films by the linear augmented-plane-wave method

    DEFF Research Database (Denmark)

    Jepsen, O.; Madsen, J.; Andersen, Ole Krogh

    1978-01-01

    We present a linear augmented-plane-wave method for solving the band-structure problem in thin crystalline films. The potential is separated into a muffin-tin potential inside the film, a potential depending exclusively on the normal coordinate outside the film, and corrections in both regions...

  4. Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure

    Directory of Open Access Journals (Sweden)

    Hao Liu

    2013-01-01

    Full Text Available A modified electromagnetic-bandgap (M-EBG structure and its application to planar monopole ultra-wideband (UWB antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1–10.6 GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX and the wireless local area network (WLAN at 3.5 GHz and 5.5 GHz, respectively.

  5. Doping and strain dependence of the electronic band structure in Ge and GeSn alloys

    Science.gov (United States)

    Xu, Chi; Gallagher, James; Senaratne, Charutha; Brown, Christopher; Fernando, Nalin; Zollner, Stefan; Kouvetakis, John; Menendez, Jose

    2015-03-01

    A systematic study of the effect of dopants and strain on the electronic structure of Ge and GeSn alloys is presented. Samples were grown by UHV-CVD on Ge-buffered Si using Ge3H8 and SnD4 as the sources of Ge and Sn, and B2H6/P(GeH3)3 as dopants. High-energy critical points in the joint-density of electronic states were studied using spectroscopic ellipsometry, which yields detailed information on the strain and doping dependence of the so-called E1, E1 +Δ1 , E0' and E2 transitions. The corresponding dependencies of the lowest direct band gap E0 and the fundamental indirect band gap Eindwere studied via room-T photoluminescence spectroscopy. Of particular interest for this work were the determination of deformation potentials, band gap renormalization effects, Burstein-Moss shifts due to the presence of carriers at band minima, and the dependence of other critical point parameters, such as amplitudes and phase angles, on the doping concentration. The selective blocking of transitions due to high doping makes it possible to investigate the precise k-space location of critical points. These studies are complemented with detailed band-structure calculations within a full-zone k-dot- p approach. Supported by AFOSR under DOD AFOSR FA9550-12-1-0208 and DOD AFOSR FA9550-13-1-0022.

  6. High Power Test on an x-Band Slotted-Iris Accelerator Structure at NLCTA

    CERN Document Server

    Adolphsen, C; Fandos, R; Grudiev, A; Heikkinen, S; Laurent, L; Rodríguez, José Alberto; Taborelli, M; Wuensch, W

    2007-01-01

    The CLIC study group at CERN has built two X-band HDS (Hybrid Damped Structure) accelerating structures for high-power testing in NLCTA at SLAC. These accelerating structures are novel with respect to their rf-design and their fabrication technique. The eleven-cell constant impedance structures, one made out of copper and one out of molybdenum, are assembled from clamped high-speed milled quadrants. They feature the same heavy higher-order-mode damping as nominal CLIC structures achieved by slotted irises and radial damping waveguides for each cell. The X-band accelerators are exactly scaled versions of structures tested at 30 GHz in the CLIC test facility, CTF3. The results of the X-band tests are presented and compared to those at 30 GHz to determine frequency scaling, and are compared to the extensive copper data from the NLC structure development program to determine material dependence and make a basic validation of the HDS design. INTRODUCTION

  7. A study using a through-space/bond interaction analysis for the band structures of substituted polyacetylene-Be systems

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Shinichirou; Aoki, Yuriko; Imamura, Akira (Dept. of Chemistry, Hiroshima Univ. (Japan))

    1990-05-01

    The band structures of dopant-polymer systems for poly(monofluoroacetylene), (C{sub 2}FH){sub x}, and poly(monohydroxyacetylene), (C{sub 2}H(OH)){sub x}, have been studied using the through-space/bond interaction analysis. It was found that these systems have small band gaps when Be atoms are used as dopants. These small gaps are caused by the band constructed mainly from the orbital of the Be atoms, and the band of Be atoms appears among the band gap of the polymer systems; these band structures are similar to those of the n-type semiconductors. The features of these donor bands near the band gaps are discussed in terms of the through-space/bond interactions by using variational and perturbational methods. Finally, in connection with these systems, a new switching system is proposed. (orig.).

  8. Quasiparticle bands and structural phase transition of iron from Gutzwiller density-functional theory

    Science.gov (United States)

    Schickling, Tobias; Bünemann, Jörg; Gebhard, Florian; Boeri, Lilia

    2016-05-01

    We use the Gutzwiller density-functional theory to calculate ground-state properties and band structures of iron in its body-centered-cubic (bcc) and hexagonal-close-packed (hcp) phases. For a Hubbard interaction U =9 eV and Hund's-rule coupling J =0.54 eV , we reproduce the lattice parameter, magnetic moment, and bulk modulus of bcc iron. For these parameters, bcc is the ground-state lattice structure at ambient pressure up to a pressure of pc=41 GPa where a transition to the nonmagnetic hcp structure is predicted, in qualitative agreement with experiment (pcexp=10 ,...,15 GPa ) . The calculated band structure for bcc iron is in good agreement with ARPES measurements. The agreement improves when we perturbatively include the spin-orbit coupling.

  9. Structural, Magnetic, and Superconducting Properties of Caged Compounds ROs2Zn20 (R = La, Ce, Pr, and Nd)

    Science.gov (United States)

    Wakiya, Kazuhei; Onimaru, Takahiro; Matsumoto, Keisuke T.; Yamane, Yu; Nagasawa, Naohiro; Umeo, Kazunori; Kittaka, Shunichiro; Sakakibara, Toshiro; Matsushita, Yoshitaka; Takabatake, Toshiro

    2017-03-01

    The electrical resistivity, magnetization, and specific heat of the caged compounds ROs2Zn20 (R = La, Ce, Pr, and Nd) have been measured to study their structural, magnetic, and superconducting properties. These measurements indicate that the compounds undergo structural transitions at Ts = 151, 109, 87, and 62 K, respectively. The decrease in Ts along with the lanthanoid contraction suggests that the high-temperature phase is more stable for a smaller lattice volume. Analysis of the lattice specific heat of LaOs2Zn20 reveals that the Zn atom at the 16c site encapsulated in the R2Zn12 cage vibrates at a low energy of 3 meV. For CeOs2Zn20, the small magnetic susceptibility with a broad maximum indicates the valence-fluctuating state of the Ce ions. In PrOs2Zn20, the crystalline electric field ground state of the 4f2 state of the Pr3+ ion remains in a non-Kramers doublet at T > Ts, which is lifted by symmetry lowering of the Pr site at T < Ts. Thereby, the quadrupolar degrees of freedom are quenched, avoiding the long-range quadrupole order. PrOs2Zn20 and LaOs2Zn20 exhibit superconducting transitions at 0.06 and 0.07 K, respectively.

  10. Synthesis of novel strontium-based cuprate superconducting thin films, and the relationship between their crystal structures and electrical properties

    Science.gov (United States)

    Chang, Kuo-Wei

    2000-12-01

    Novel Sr-based cuprate thin films were investigated to explore their potential as next generation superconducting materials. Thin films of infinite-layer compound (Sr,Ca)CuO2 (no blocking layer), cuprate oxycarbonate Sr2CuO2(CO3) (carbonate blocking layer), and Tl(Sr,Ba)2Can-1CunOy (n = 2 and 3) (thin blocking layer) were synthesized using metal-organic chemical vapor deposition. The structure and defect chemistry of the blocking layers of these cuprate compounds were found to have profound effects on the transport properties both in the normal state and the superconducting state. Phase pure, epitaxial infinite-layer compound (Sr1-xCa x)CuO2 thin films were deposited on SrTiO3(100) substrates. However, these films were always semiconducting with resistivities of the order of 1 ohm- cm and with carrier concentrations of 1017~10 19cm-3, which is two to four orders of magnitude lower than the typical superconducting cuprates. The low carrier concentration was attributed to the absence of blocking layers containing a sufficient concentration of charged defects. Transport was via variable range hopping conduction. By annealing in air, the infinite-layer compound SrCuO2 thin films reacted with the CO2 in air to generate Sr 2CuO2(CO3) thin films. Upon formation of carbonate blocking layers, charger carriers were introduced into the Sr2CuO 2(CO3) thin films through the partial substitution of carbon by copper or boron in the SrCO3 blocking layers. After oxygen annealing or upon boron substitution, the carrier concentration increased up to 10 21 cm-3. A superconducting onset temperature of 34K and a zero resistivity temperature of 20K have been observed for Sr 2CuO2(C1-xBx)O3 thin films. A critical carrier density of 0.10~0.12 holes/Cu was required to render superconductivity. The effect of crystal structure on the critical current density was investigated by measuring the vortex pinning energies of Tl2Ba2CaCu 2Oy (Tl-2212) and Tl(Sr,Ba)2Ca Cu2O y (Tl- (Sr,Ba)1212) thin

  11. Superconductivity in Potassium-Doped Metallic Polymorphs of MoS2.

    Science.gov (United States)

    Zhang, Renyan; Tsai, I-Ling; Chapman, James; Khestanova, Ekaterina; Waters, John; Grigorieva, Irina V

    2016-01-13

    Superconducting layered transition metal dichalcogenides (TMDs) stand out among other superconductors due to the tunable nature of the superconducting transition, coexistence with other collective electronic excitations (charge density waves), and strong intrinsic spin-orbit coupling. Molybdenum disulfide (MoS2) is the most studied representative of this family of materials, especially since the recent demonstration of the possibility to tune its critical temperature, Tc, by electric-field doping. However, just one of its polymorphs, band-insulator 2H-MoS2, has so far been explored for its potential to host superconductivity. We have investigated the possibility to induce superconductivity in metallic polytypes, 1T- and 1T'-MoS2, by potassium (K) intercalation. We demonstrate that at doping levels significantly higher than that required to induce superconductivity in 2H-MoS2, both 1T and 1T' phases become superconducting with Tc = 2.8 and 4.6 K, respectively. Unusually, K intercalation in this case is responsible both for the structural and superconducting phase transitions. By adding new members to the family of superconducting TMDs, our findings open the way to further manipulate and enhance the electronic properties of these technologically important materials.

  12. Investigation of band structure of {sup 103,105}Rh using microscopic computational technique

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Amit, E-mail: akbcw2@gmail.com [Research Scholar, Department of Physics and Electronics, University of Jammu, Jammu-180006 (India); Singh, Suram, E-mail: suramsingh@gmail.com [Assistant Professor, Department of Physics Govt. Degree College, Kathua-184142 (India); Bharti, Arun, E-mail: arunbharti-2003@yahoo.co.in [Professor, Department of Physics and Electronics, University of Jammu, Jammu-180006 (India)

    2015-08-28

    The high-spin structure in {sup 61}Cu nucleus is studied in terms of effective two body interaction. In order to take into account the deformed BCS basis, the basis states are expanded in terms of the core eigenfunctions. Yrast band with some other bands havew been obtained and back-bending in moment of inertia has also been calculated and compared with the available experimental data for {sup 61}Cu nucleus. On comparing the available experimental as well as other theoretical data, it is found that the treatment with PSM provides a satisfactory explanation of the available data.

  13. Flexural vibration band gaps in thin plates with two-dimensional binary locally resonant structures

    Institute of Scientific and Technical Information of China (English)

    Yu Dian-Long; Wang Gang; Liu Yao-Zong; Wen Ji-Hong; Qiu Jing

    2006-01-01

    The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically placed in a host material. Numerical simulations show that the low-frequency gaps of flexural wave exist in the thin plates. The width of the first gap decreases monotonically as the matrix density increases. The frequency response of the finite periodic thin plates is simulated by the finite element method, which provides attenuations of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.

  14. Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic-Organic Hybrids.

    Science.gov (United States)

    Roy, Soumyabrata; Sarkar, Sumanta; Pan, Jaysree; Waghmare, Umesh V; Dhanya, R; Narayana, Chandrabhas; Peter, Sebastian C

    2016-04-04

    We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations.

  15. Electronic band structure effects in the stopping of protons in copper

    Science.gov (United States)

    Quashie, Edwin E.; Saha, Bidhan C.; Correa, Alfredo A.

    2016-10-01

    We present an ab initio study of the electronic stopping power of protons in copper over a wide range of proton velocities v =0.02 -10 a .u . where we take into account nonlinear effects. Time-dependent density functional theory coupled with molecular dynamics is used to study electronic excitations produced by energetic protons. A plane-wave pseudopotential scheme is employed to solve the time-dependent Kohn-Sham equations for a moving ion in a periodic crystal. The electronic excitations and the band structure determine the stopping power of the material and alter the interatomic forces for both channeling and off-channeling trajectories. Our off-channeling results are in quantitative agreement with experiments, and at low velocity they unveil a crossover region of superlinear velocity dependence (with a power of ˜1.5 ) in the velocity range v =0.07 -0.3 a .u . , which we associate to the copper crystalline electronic band structure. The results are rationalized by simple band models connecting two separate regimes. We find that the limit of electronic stopping v →0 is not as simple as phenomenological models suggest and it is plagued by band-structure effects.

  16. Electronic structure and optical properties of noncentrosymmetric LiGaSe2: Experimental measurements and DFT band structure calculations

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.

    2017-04-01

    We report on measurements of X-ray photoelectron (XP) spectra for pristine and Ar+ ion-irradiated surfaces of LiGaSe2 single crystal grown by Bridgman-Stockbarger method. Electronic structure of the LiGaSe2 compound is studied from a theoretical and experimental viewpoint. In particular, total and partial densities of states of LiGaSe2 are investigated by density functional theory (DFT) calculations employing the augmented plane wave + local orbitals (APW + lo) method and they are verified by data of X-ray spectroscopy measurements. The DFT calculations indicate that the main contributors to the valence band of LiGaSe2 are the Se 4p states, which contribute mainly at the top and in the upper portion of the valence band, with also essential contributions of these states in the lower portion of the band. Other substantial contributions to the valence band of LiGaSe2 emerge from the Ga 4s and Ga 4p states contributing mainly at the lower ant upper portions of the valence band, respectively. With respect to the conduction band, the calculations indicate that its bottom is composed mainly from contributions of the unoccupied Ga s and Se p states. The present calculations are confirmed experimentally when comparing the XP valence-band spectrum of the LiGaS2 single crystal on a common energy scale with the X-ray emission bands representing the energy distribution of the Ga 4p and Se 4p states. Measurements of the fundamental absorption edges at room temperature reveal that bandgap value, Eg, of LiGaSe2 is equal to 3.47 eV and the Eg value increases up to 3.66 eV when decreasing temperature to 80 K. The main optical characteristics of the LiGaSe2 compound are clarified by the DFT calculations.

  17. Disorder effects on the band structure of ZnGeN2: Role of exchange defects

    Science.gov (United States)

    Skachkov, Dmitry; Quayle, Paul C.; Kash, Kathleen; Lambrecht, Walter R. L.

    2016-11-01

    The role of exchange defects on the band structure of ZnGeN2 is investigated. Exchange defects are defined through the exchange of cations Zn and Ge starting from the ideal P n a 21 crystal structure, which obeys the local octet rule. Each such exchange creates several nitrogen-centered tetrahedra which violate the local octet rule, although overall charge neutrality is preserved. We study several distributions of exchange defects, some with all antisites making up the exchange defect close to each other and with increasing numbers of exchange defects, and others where the two types of antisites ZnGe and GeZn are kept separated from each other. We also compare the results for these models with a fully random distribution of Zn and Ge on the cation sites. We show that for a single-nearest-neighbor exchange defect, the band gap is narrowed by about 0.5 eV due to two effects: (1) the ZnGe antisites form filled acceptor states just above and merging with the valence-band maximum (VBM) of perfect crystal ZnGeN2 and (2) the GeZn antisites form a resonance in the conduction band which lowers the conduction-band minimum (CBM). When more exchange defects are created, these acceptor states broaden into bands which can lower the gap further. When tetrahedra occur surrounded completely by four Zn atoms, states even deeper in the gap are found localized all near these tetrahedra, forming a separate intermediate band. Finally, for phase-segregated ZnGe and GeZn, the gap is significantly more reduced, but no separate band is found to occur. The ZnGe acceptorlike states now form a percolating defect band which is significantly wider and hence reaches deeper into the gap. In all cases, the wave functions near the top of the new VBM remain, to some extent, localized near the ZnGe sites. For a fully random case, the gap is even more severely reduced by almost 3 eV. The total energy of the system increases with the number of octet-rule-violating tetrahedra and the energy cost per

  18. Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying

    DEFF Research Database (Denmark)

    Canulescu, Stela; Rechendorff, K.; Borca, C. N.;

    2014-01-01

    The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at. %. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms...... are not located in a TiO2 unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2 eV (300–135 nm). The results indicate that amorphous anodic Al2O3 has a direct...

  19. Ab initio electronic band structure study of III-VI layered semiconductors

    Science.gov (United States)

    Olguín, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrés

    2013-08-01

    We present a total energy study of the electronic properties of the rhombohedral γ-InSe, hexagonal ɛ-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.

  20. Superconductivity and metallic behavior in Pb{sub x}C{sub y}O{sub δ} structures prepared by focused electron beam induced deposition

    Energy Technology Data Exchange (ETDEWEB)

    Winhold, M., E-mail: winhold@Physik.uni-frankfurt.de; Weirich, P. M.; Schwalb, C. H.; Huth, M. [Physikalisches Institut, Goethe-University, 60438 Frankfurt am Main (Germany)

    2014-10-20

    Focused electron beam induced deposition as a direct-write approach possesses great potential to meet the demands for superconducting nanostructure fabrication especially regarding its 3D patterning capabilities combined with the high resolution in the nanometer regime. So far, however, it was not possible to fabricate superconducting structures with this technique. In this work, we present a lead-based superconductor prepared by focused electron beam induced deposition by dissociation of the precursor tetraethyllead. The as-grown structures exhibit metallic behavior and a minimum resistivity in the normal state of ρ = 16 μΩcm at T = 9 K followed by a superconducting transition at T{sub c} = 7.2 K.

  1. Ground-based testing of the dynamics of flexible space structures using band mechanisms

    Science.gov (United States)

    Yang, L. F.; Chew, Meng-Sang

    1991-01-01

    A suspension system based on a band mechanism is studied to provide the free-free conditions for ground based validation testing of flexible space structures. The band mechanism consists of a noncircular disk with a convex profile, preloaded by torsional springs at its center of rotation so that static equilibrium of the test structure is maintained at any vertical location; the gravitational force will be directly counteracted during dynamic testing of the space structure. This noncircular disk within the suspension system can be configured to remain unchanged for test articles with the different weights as long as the torsional spring is replaced to maintain the originally designed frequency ratio of W/k sub s. Simulations of test articles which are modeled as lumped parameter as well as continuous parameter systems, are also presented.

  2. Band structure and itinerant magnetism in quantum critical NbFe2

    Energy Technology Data Exchange (ETDEWEB)

    Subedi, A. P. [University of Tennessee, Knoxville (UTK); Singh, David J [ORNL

    2010-01-01

    We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.

  3. Robust topology optimization of three-dimensional photonic-crystal band-gap structures

    CERN Document Server

    Men, Han; Freund, Robert M; Peraire, Jaime; Johnson, Steven G

    2014-01-01

    We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniq...

  4. Study on Band Structure of YbB6 and Analysis of Its Optical Conductivity Spectrum

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The electronic structure of YbB6 crystal was studied by means of density functional (GGA+U) method.The calculations were performed by FLAPW method.The high accurate band structure was achieved.The correlation between the feature of the band structure and the Yb-B6 bonding in YbB6 was analyzed.On this basis, some optical constants of YbB6 such as reflectivity, dielectric function, optical conductivity, and energy-loss function were calculated.The results are in good agreement with the experiments.The real part of the optical conductivity spectrum and the energy-loss function spectrum were analyzed in detail.The assignments of the spectra were carried out to correlate the spectral peaks with the interband electronic transitions, which justify the reasonable part of previous empirical assignments and renew the missed or incorrect ones.

  5. Broadband sample holder for microwave spectroscopy of superconducting qubits.

    Science.gov (United States)

    Averkin, A S; Karpov, A; Shulga, K; Glushkov, E; Abramov, N; Huebner, U; Il'ichev, E; Ustinov, A V

    2014-10-01

    We present a practical design and implementation of a broadband sample holder suitable for microwave experiments with superconducting integrated circuits at millikelvin temperatures. Proposed design can be easily integrated in standard dilution cryostats, has flat pass band response in a frequency range from 0 to 32 GHz, allowing the RF testing of the samples with substrate size up to 4 × 4 mm(2). The parasitic higher modes interference in the holder structure is analyzed and prevented via design considerations. The developed setup can be used for characterization of superconducting parametric amplifiers, bolometers, and qubits. We tested the designed sample holder by characterizing of a superconducting flux qubit at 20 mK temperature.

  6. Introduction of DC line structures into a superconducting microwave 3D cavity

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Wei-Cheng; Deng, Guang-Wei; Li, Shu-Xiao; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guo-Ping, E-mail: gpguo@ustc.edu.cn [Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026, China and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2015-02-15

    We report a technique that can noninvasively add multiple DC wires into a 3D superconducting microwave cavity for electronic devices that require DC electrical terminals. We studied the influence of our DC lines on the cavity performance systematically. We found that the quality factor of the cavity is reduced if any of the components of the electrical wires cross the cavity equipotential planes. Using this technique, we were able to incorporate a quantum dot (QD) device into a 3D cavity. We then controlled and measured the QD transport signal using the DC lines. We have also studied the heating effects of the QD by the microwave photons in the cavity.

  7. Large-Area Superconducting Nanowire Single-Photon Detector with Double-Stage Avalanche Structure

    OpenAIRE

    2016-01-01

    We propose a novel design of superconducting nanowire avalanche photodetectors (SNAPs), which combines the advantages of multi-stage avalanche SNAPs to lower the avalanche current I_AV and that of series-SNAPs to reduce the reset time. As proof of principle, we fabricated 800 devices with large detection area (15 um * 15 um) and five different designs on a single silicon chip for comparison, which include standard SNSPDs, series-3-SNAPs and our modified series-SNAPs with double-stage avalanch...

  8. Structural and low-field magnetic characterization of superconducting MgB{sub 2} wires

    Energy Technology Data Exchange (ETDEWEB)

    Kilic, A. [Faculty of Sciences, Department of Physics, Ankara University, 06100-Tandogan/Ankara (Turkey); Okur, S. [Izmir Institute of Technology, Department of Physics, 35437-Urla/Izmir (Turkey); Gueclue, N. [Faculty of Sciences and Art, Department of Physics, Gaziosmanpasa University, 60100-Taslicftlik/Tokat (Turkey)]. E-mail: guclu06@hotmail.com; Koelemen, U. [Faculty of Sciences and Art, Department of Physics, Gaziosmanpasa University, 60100-Taslicftlik/Tokat (Turkey); Uzun, O. [Faculty of Sciences and Art, Department of Physics, Gaziosmanpasa University, 60100-Taslicftlik/Tokat (Turkey); Oezyuezer, L. [Izmir Institute of Technology, Department of Physics, 35437-Urla/Izmir (Turkey); Gencer, A. [Faculty of Sciences, Department of Physics, Ankara University, 06100-Tandogan/Ankara (Turkey)

    2004-10-01

    Superconducting MgB{sub 2} composite wires were prepared by packing blend of MgB{sub 2} inside of Cu tubes using powder in tube (PIT) method. The produced samples of the wires were then characterised by using SEM, XRD and AC susceptibility measurements. The measured fundamental susceptibility is compared with Bean model. We have obtained an empirical functions for the penetration field H{sub p} = H{sub {alpha}}(1-t){sup {beta}}, where t is the reduced temperature. In addition, ac losses were calculated at the same fixed temperatures to compare theoretical solutions. There is a qualitative agreement between the experimental results and theory.

  9. Structural, elastic and electronic properties of superconducting anti-perovskites MgCNi{sub 3}, ZnCNi{sub 3} and CdCNi{sub 3} from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Shein, I.R.; Bannikov, V.V. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620041, Ekaterinburg (Russian Federation); Ivanovskii, A.L. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620041, Ekaterinburg (Russian Federation)], E-mail: ivanovskii@ihim.uran.ru

    2008-01-01

    First principle total energy calculations using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential were performed to investigate the systematic trends for structural, elastic and electronic properties of the family of superconducting anti-perovskites MCNi{sub 3} depending from the type of M cations (M are Mg, Zn and Cd). In result the optimized lattice parameters, independent elastic constants (C{sub 11}, C{sub 12} and C{sub 44}), bulk modulus B, compressibility {beta}, shear modulus G and tetragonal shear modulus G' are evaluated. Further, for the first time the numerical estimates of a set of elastic parameters (bulk and shear modulus, Young's modulus Y, Poisson's ratio ({nu}), Lame's coefficients ({mu}, {lambda})) of the polycrystalline superconducting MCNi{sub 3} ceramics (in framework of the Voigt-Reuss-Hill approximation) were performed. Besides, the band structures, densities of states (DOS), total and site-projected l-decomposed DOS at the Fermi level, the shapes of the Fermi surfaces, the Sommerfeld's coefficients and the molar Pauli paramagnetic susceptibility for these anti-perovskites were obtained and analyzed in comparison with the available theoretical and experimental data.

  10. Structural and superconducting properties of LaFeAs1-xSbxO1-yFy

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    We report the antimony(Sb) doping effect in a prototype system of iron-based superconductors LaFeAsO1-yFy(y=0,0.1,0.15).X-ray powder diffraction indicates that the lattice parameters increase with Sb content within the doping limit.Rietveld structural refinements show that,with the partial substitution of Sb for As,the thickness of the Fe2As2 layers increases significantly,whereas that of the La2O2 layers shrinks simultaneously.So a negative chemical pressure is indeed "applied" to the superconducting-active Fe2As2 layers,in contrast to the effect of positive chemical pressure by the phosphorus doping.Electrical resistance and magnetic susceptibility measurements indicate that,while the Sb doping hardly influences the SDW anomaly in LaFeAsO,it recovers SDW order for the optimally-doped sample of y=0.1.In the meantime,the superconducting transition temperature can be raised up to 30 K in LaFeAs1-xSbxO1-yFy with x=0.1 and y=0.15.The Sb doping effects are discussed in term of both J1-J2 model and Fermi Surface(FS) nesting scenario.

  11. Study on effect of annealing conditions on structural, magnetic and superconducting properties of MgB{sub 2} bulk samples

    Energy Technology Data Exchange (ETDEWEB)

    Phaneendra, Konduru, E-mail: phaneendra-50@yahoo.com; Asokan, K., E-mail: phaneendra-50@yahoo.com; Kanjilal, D. [Inter University Accelerator Centre, Aruna Asaf Ali Marg, Vasanth Kung, New Delhi-110067 (India); Awana, V. P. S. [Quantum Phenomena and Applications, National Physical Laboratory, K S Krishnan Marg, New Delhi-110012 (India); Sastry, S. Sreehari [Dept. of Physics, Acharya Nagarjuna University, Guntur-522510 (India)

    2014-04-24

    Effect of annealing conditions on structural, magnetic and superconducting properties of Magnesium Diboride (MgB{sub 2}) bulk superconductor samples prepared by solid state route method are compared. The samples are made by taking Magnesium and Boron powders in stoichiometric ratio, grounded well and pelletized at pressure of about 10Tonnes. These pellets are annealed in both Argon and vacuum environment separately up to 800°c for two hours. Both the samples show clear superconducting transition at Tc ∼ 38 k. This is further conformed by AC/DC magnetization (M-T), Resistivity [ρ (T, H)] measurements under magnetic field up to 14 Tesla as well. Rietveld refinement of X-ray diffraction of both samples conformed the MgB{sub 2} phase formation with P6/mmm space group symmetry. Scanning Electron Microscopy images of the surface revile more agglomeration of grains in case of Argon annealed samples. This result in more critical current density (J{sub c}) of Argon annealed samples than vacuum annealed one calculated from Bean's critical state model. This high Jc is explained in terms of more inter grain connectivity for Argon annealed sample than vacuum annealed sample.

  12. Study on effect of annealing conditions on structural, magnetic and superconducting properties of MgB2 bulk samples

    Science.gov (United States)

    Phaneendra, Konduru; Asokan, K.; Awana, V. P. S.; Sastry, S. Sreehari; Kanjilal, D.

    2014-04-01

    Effect of annealing conditions on structural, magnetic and superconducting properties of Magnesium Diboride (MgB2) bulk superconductor samples prepared by solid state route method are compared. The samples are made by taking Magnesium and Boron powders in stoichiometric ratio, grounded well and pelletized at pressure of about 10Tonnes. These pellets are annealed in both Argon and vacuum environment separately up to 800°c for two hours. Both the samples show clear superconducting transition at Tc ˜ 38 k. This is further conformed by AC/DC magnetization (M-T), Resistivity [ρ (T, H)] measurements under magnetic field up to 14 Tesla as well. Rietveld refinement of X-ray diffraction of both samples conformed the MgB2 phase formation with P6/mmm space group symmetry. Scanning Electron Microscopy images of the surface revile more agglomeration of grains in case of Argon annealed samples. This result in more critical current density (Jc) of Argon annealed samples than vacuum annealed one calculated from Bean's critical state model. This high Jc is explained in terms of more inter grain connectivity for Argon annealed sample than vacuum annealed sample.

  13. Normal state electronic structure and the superconducting energy gap in HTSC's as determined from photoemission spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Arko, A.J.; List, R.S.; Bartlett, R.J.; Cheong, S.W.; Fisk, Z.; Thompson, J.D. (Los Alamos National Lab., NM (USA)); Olson, C.G.; Yang, A.B.; Liu, R.; Gu, C. (Ames Lab., IA (USA)); Veal, B.W.; Liu, J.Z.; Paulikas, A.P.; Vandervoort, K.; Claus, H.; Campuzano, J.C. (Argonne National Lab., IL (USA))

    1989-01-01

    Photoemission spectroscopy has been utilized to determine the electronic structure of high-T{sub c} materials. The observation of dispersive bands at E{sub F} suggests a Fermi surface similar to that obtained from a band calculation. The results apparently are not inconsistent with the notion of a correlated Fermi liquid consisting of hybridized p-d bands. However, it is becoming more and more difficult to distinguish between Fermi liquid behavior in the new high-T{sub c} superconductors and behavior expected on the basis of the novel new non-Fermi liquid theories. The differences are now predicted to be on an energy scale smaller than our experimental resolution. We point out that, while deviations from simple band theory certainly do exist in the form of core and valence band satellites, band narrowing, and rapid photoemission peak broadening away from E{sub F}, there are sufficient agreements with the overall DOS that it should be considered a good starting point for the electronic structure. For example, the calculated Fermi surface for both the 123 and 2212 structures is reasonably well reproduced experimentally and the bands at E{sub F} consist of p-d hybridized orbitals just as predicted by local density functional theory. Our spectra clearly show that a BCS-like DOS is obtained at the Fermi energy as a gap opens up below T{sub c}. This is just one more indication that the old conventional models should be considered more seriously. 18 refs., 6 figs.

  14. Banded structures in electron pitch angle diffusion coefficients from resonant wave-particle interactions

    Science.gov (United States)

    Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

    2016-04-01

    Electron pitch angle (Dαα) and momentum (Dpp) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies ≤10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = ±1, ±2, … ±5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (α) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in Dαα and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than Dαα coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than Dαα coefficients for the case n ≠ 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of Dαα coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89° and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle 10° and Landau

  15. Directional point-contact spectroscopy of MgB$_{2}$ single crystals in magnetic fields two-band superconductivity and critical fields

    CERN Document Server

    Gonnelli, R S; Ummarino, G A; Della Rocca, V; Calzolari, A; Stepanov, V A; Jun, J; Kazakov, S M; Karpinski, J; Dellarocca, Valeria

    2004-01-01

    The results of the first directional point-contact measurements in MgB2 single crystals, in the presence of magnetic fields up to 9 T either parallel or perpendicular to the ab planes, are presented. By applying suitable magnetic fields, we separated the partial contributions of the sigma and pi bands to the total Andreev-reflection conductance. Their fit with the BTK model allowed a very accurate determination of the temperature dependency of the gaps (Delta_sigma and Delta_pi), that resulted in close agreement with the predictions of the two-band models for MgB2. We also obtained, for the first time with point-contact spectroscopy, the temperature dependence of the (anisotropic) upper critical field of the sigma band and of the (isotropic) upper critical field of the pi band.

  16. Chromosome banding and gene localizations support extensive conservation of chromosome structure between cattle and sheep.

    Science.gov (United States)

    Hediger, R; Ansari, H A; Stranzinger, G F

    1991-01-01

    By using three gene probes, one derived from the porcine major histocompatibility complex (MHC) and two from bovine cytokeratin genes, type I (KRTA) and type II (KRTB), the hypothesis of conservation of genome structure in two members of the family Bovidae was examined. Gene mapping data revealed the MHC to be in chromosome region 23q15----q23 in cattle (BOLA) and 20q15----q23 in sheep (OLA). KRTA was localized to chromosome region 19q25----q29 in cattle and 11q25----q29 in sheep and KRTB to 5q14----q22 in cattle and 3q14----q22 in sheep. The banding patterns of the chromosome arms to which the loci were assigned were identical in both species. Moreover, the resemblances of GTG- or QFQ-banding patterns between the cattle and sheep karyotypes illustrated further chromosome homologies. These studies, based on gene mapping comparisons and comparative cytogenetics, document that within bovid chromosomes, homology of banding patterns corresponds to a homologous genetic structure. Hence, we propose that gene assignments on identified chromosomal segments in one species of the Bovidae can be extrapolated, in general, to other bovid species based on the banding homologies presented here.

  17. Determination of the band structure of LuNi{sub 2}B{sub 2}C

    Energy Technology Data Exchange (ETDEWEB)

    Bergk, B. [Hochfeld-Magnetlabor, Forschungszentrum Rossendorf, Dresden (Germany); Inst. fuer Festkoerperphysik, Technische Univ. Dresden (Germany); Bartkowiak, M.; Ignatchik, O. [Hochfeld-Magnetlabor, Forschungszentrum Rossendorf, Dresden (Germany); Jaeckel, M. [Inst. fuer Festkoerperphysik, Technische Univ. Dresden (Germany); Wosnitza, J.; Rosner, H.; Petzold, V. [MPI fuer chemische Physik fester Stoffe, Dresden (Germany); Canfield, P. [Iowa State Univ. of Science and Technology, Ames (United States). Ames Lab., Condensed Matter Physics

    2007-07-01

    We present de Haas-van Alphen (dHvA) investigations on the nonmagnetic borocarbide superconductor LuNi{sub 2}B{sub 2}C which have been performed by use of the torque method in high magnetic fields up to 32 T and at low temperatures down to 50 mK. The complex band structure is extracted from the quantum oscillations in the normal state. In comparison with full-potential-local-orbital calculations of the band structure we are able to assign the observed dHvA frequencies to the different bands. Temperature dependent dHvA investigations allowed the extraction of the effective band masses for the several Fermi-surface sheets. We observe an enhancement of the effective masses compared to the theoretical calculations which is due to electron-phonon interaction. Finally, we are able to examine the angular dependence of the electron-phonon coupling for the different Fermi-surface sheets. (orig.)

  18. Electronic band structure of a Tl/Sn atomic sandwich on Si(111)

    Science.gov (United States)

    Gruznev, D. V.; Bondarenko, L. V.; Matetskiy, A. V.; Tupchaya, A. Y.; Alekseev, A. A.; Hsing, C. R.; Wei, C. M.; Eremeev, S. V.; Zotov, A. V.; Saranin, A. A.

    2015-01-01

    A two-dimensional compound made of one monolayer of Tl and one monolayer of Sn on Si(111) has been found to have a sandwichlike structure in which the Sn layer (having the milk-stool arrangement) resides on the bulklike terminated Si(111) surface and the Tl layer (having the honeycomb-chained-trimer arrangement) is located above the Sn layer. The electronic band structure of the compound contains two spin-split surface-state bands, of which one is nonmetallic and the other is metallic. Near the Fermi level the metallic band is split with the momentum splitting Δ k∥=0.037 Å-1 and energy splitting Δ EF=167 meV. The steep dispersion of the band when crossing the Fermi level corresponds to an electron velocity of ≈8.5 ×105 m/s, which is comparable to the value reported for graphene. The 2D Fermi contours have almost circular shape with spin texture typical for hexagonal surfaces.

  19. Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects

    Science.gov (United States)

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-09-01

    Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

  20. Strain effect on graphene nanoribbon carrier statistic in the presence of non-parabolic band structure

    Science.gov (United States)

    Izuani Che Rosid, N. A.; Ahmadi, M. T.; Ismail, Razali

    2016-09-01

    The effect of tensile uniaxial strain on the non-parabolic electronic band structure of armchair graphene nanoribbon (AGNR) is investigated. In addition, the density of states and the carrier statistic based on the tight-binding Hamiltonian are modeled analytically. It is found that the property of AGNR in the non-parabolic band region is varied by the strain. The tunable energy band gap in AGNR upon strain at the minimum energy is described for each of n-AGNR families in the non-parabolic approximation. The behavior of AGNR in the presence of strain is attributed to the breakable AGNR electronic band structure, which varies the physical properties from its normality. The linear relation between the energy gap and the electrical properties is featured to further explain the characteristic of the deformed AGNR upon strain. Project supported by the Ministry of Higher Education (MOHE), Malaysia under the Fundamental Research Grant Scheme (FRGS) (Grant No.Q.J130000.7823.4F477). We also thank the Research Management Center (RMC) of Universiti Teknologi Malaysia (UTM) for providing an excellent research environment.

  1. Triaxial projected shell model description of high-spin band-structures in {sup 103,105}Rh isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Bhat, G.H. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Sheikh, J.A., E-mail: sjaphysics@gmail.com [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Dar, W.A. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Jehangir, S. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Department of Physics, National Institute of Technology, Srinagar 190 006 (India); Palit, R., E-mail: palit@tifr.res.in [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Colaba, Mumbai (India); Ganai, P.A. [Department of Physics, University of Kashmir, Srinagar 190 006 (India); Department of Physics, National Institute of Technology, Srinagar 190 006 (India)

    2014-11-10

    High-spin band structures in odd-proton {sup 103,105}Rh are investigated using the microscopic triaxial projected shell model approach. It is demonstrated that the observed band structures built on one- and three-quasiparticle states are reproduced reasonably well in the present work. Further, it is evident from the analysis of the projected wavefunctions that side-band in the low-spin regime is the normal γ-band built on the ground-state configuration. However, in the high-spin regime, the side band is shown to be highly mixed and ceases to be a γ-band. We provide a complete set of electromagnetic transition probabilities for the two bands and the experimental measurements are desirable to test the predictions of the present work.

  2. Two-dimensional microwave band-gap structures of different dielectric materials

    Indian Academy of Sciences (India)

    E D V Nagesh; G Santosh Babu; V Subramanian; V Sivasubramanian; V R K Murthy

    2005-12-01

    We report the use of low dielectric constant materials to form two-dimensional microwave band-gap structures for achieving high gap-to-midgap ratio. The variable parameters chosen are the lattice spacing and the geometric structure. The selected geometries are square and triangular and the materials chosen are PTFE ( = 2.1), PVC ( = 2.38) and glass ( = 5.5). Using the plane-wave expansion method, proper lattice spacing is selected for each structure and material. The observed experimental results are analyzed with the help of the theoretical prediction.

  3. Alternative structure of TiO2 with higher energy valence band edge

    Science.gov (United States)

    Coh, Sinisa; Yu, Peter Y.; Aoki, Yuta; Saito, Susumu; Louie, Steven G.; Cohen, Marvin L.

    2017-02-01

    We propose an alternative structure of TiO2 anatase that has a higher energy oxygen p -like valence band maximum than pristine TiO2 anatase and thus has a much better alignment with the water splitting levels. This alternative structure is unique when considering a large subspace of possible structural distortions of TiO2 anatase. We propose two routes towards this state and argue that one of them might have been realized in the recently discovered so-called black TiO2.

  4. Structural and magnetic phase diagram of CeFeAsO(1- x)F(x) and its relation to high-temperature superconductivity.

    Science.gov (United States)

    Zhao, Jun; Huang, Q; de la Cruz, Clarina; Li, Shiliang; Lynn, J W; Chen, Y; Green, M A; Chen, G F; Li, G; Li, Z; Luo, J L; Wang, N L; Dai, Pengcheng

    2008-12-01

    Recently, high-transition-temperature (high-Tc) superconductivity was discovered in the iron pnictide RFeAsO(1-x)F(x) (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO(1-x)F(x) as the system is tuned from a semimetal to a high-Tc superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x=0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x>0.06, resulting in an electronic phase diagram remarkably similar to that of the high-Tc copper oxides. Comparison of the structural evolution of CeFeAsO(1-x)F(x) with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-Tc superconductivity in these Fe pnictides.

  5. Band Gap Opening Induced by the Structural Periodicity in Epitaxial Graphene Buffer Layer.

    Science.gov (United States)

    N Nair, Maya; Palacio, Irene; Celis, Arlensiú; Zobelli, Alberto; Gloter, Alexandre; Kubsky, Stefan; Turmaud, Jean-Philippe; Conrad, Matthew; Berger, Claire; de Heer, Walter; Conrad, Edward H; Taleb-Ibrahimi, Amina; Tejeda, Antonio

    2017-04-12

    The epitaxial graphene buffer layer on the Si face of hexagonal SiC shows a promising band gap, of which the precise origin remains to be understood. In this work, we correlate the electronic to the atomic structure of the buffer layer by combining angle resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), and high-resolution scanning transmission electron microscopy (HR-STEM). We show that the band structure in the buffer has an electronic periodicity related to the structural periodicity observed in STM images and published X-ray diffraction. Our HR-STEM measurements show the bonding of the buffer layer to the SiC at specific locations separated by 1.5 nm. This is consistent with the quasi 6 × 6 periodic corrugation observed in the STM images. The distance between buffer C and SiC is 1.9 Å in the bonded regions and up to 2.8 Å in the decoupled regions, corresponding to a 0.9 Å corrugation of the buffer layer. The decoupled regions are sp(2) hybridized. Density functional tight binding (DFTB) calculations demonstrate the presence of a gap at the Dirac point everywhere in the buffer layer, even in the decoupled regions where the buffer layer has an atomic structure close to that of graphene. The surface periodicity also promotes band in the superperiodic Brillouin zone edges as seen by photoemission and confirmed by our calculations.

  6. Kinetic Inductance Photodetectors Based on Nonequilibrium Response in Superconducting Thin-Film Structures

    Science.gov (United States)

    Sergeev, A. V.; Karasik, B. S.; Gogidze, I. G.; Mitin, V. V.

    2001-01-01

    While experimental studies of kinetic-inductance sensors have been limited so far by the temperature range near the superconducting transition, these detectors can be very sensitivity at temperatures well below the transition, where the number of equilibrium quasiparticles is exponentially small. In this regime, a shift of the quasiparticle chemical potential under radiation results in the change of the kinetic inductance, which can be measured by a sensitive SQUID readout. We modeled the kinetic inductance response of detectors made from disordered superconducting Nb, NbC, and MoRe films. Low phonon transparency of the interface between the superconductor and the substrate causes substantial re-trapping of phonons providing high quantum efficiency and the operating time of approximately 1 ms at 1 K. Due to the small number of quasiparticles, the noise equivalent power of the detector determined by the quasiparticle generation-recombination noise can be as small as approximately 10(exp -19) W/Hz(exp 1/2) at He4 temperatures.

  7. Response of superconductivity and crystal structure of LiFeAs to hydrostatic pressure.

    Science.gov (United States)

    Mito, Masaki; Pitcher, Michael J; Crichton, Wilson; Garbarino, Gaston; Baker, Peter J; Blundell, Stephen J; Adamson, Paul; Parker, Dinah R; Clarke, Simon J

    2009-03-04

    On the application of hydrostatic pressures of up to 1.3 GPa, the superconducting transition temperatures (T(c)) of samples of LiFeAs are lowered approximately monotonically at approximately -2 K GPa(-1). Measurements of the X-ray powder diffraction pattern at hydrostatic pressures of up to 17 GPa applied by a He gas pressure medium in a diamond anvil cell reveal a bulk modulus for LiFeAs of 57.3(6) GPa which is much smaller than that of other layered arsenide and oxyarsenide superconductors. LiFeAs also exhibits much more isotropic compression than other layered iron arsenide superconductors. The higher and more isotropic compressibility is presumably a consequence of the small size of the lithium ion. At ambient pressure the FeAs(4) tetrahedra are the most compressed in the basal plane of those in any of the superconducting iron arsenides. On increasing the pressure the Fe-Fe distance contracts more rapidly than the Fe-As distance so that the FeAs(4) tetrahedra become even more distorted from the ideal tetrahedral shape. The decrease in T(c) with applied pressure is therefore consistent with the observations that in the iron arsenides and related materials investigated thus far, T(c) is maximized for a particular electron count when the FeAs(4) tetrahedra are close to regular.

  8. Fabrication and superconducting properties of a simple-structured jelly-roll Nb{sub 3}Al wire with low-temperature heat-treatment

    Energy Technology Data Exchange (ETDEWEB)

    Cui, L.J. [National Engineering Laboratory for Superconducting Materials (NELSM), Western Superconducting Technologies (WST) Co. Ltd., Xi’an 710018 (China); Yan, G., E-mail: gyan@c-wst.com [National Engineering Laboratory for Superconducting Materials (NELSM), Western Superconducting Technologies (WST) Co. Ltd., Xi’an 710018 (China); Pan, X.F. [National Engineering Laboratory for Superconducting Materials (NELSM), Western Superconducting Technologies (WST) Co. Ltd., Xi’an 710018 (China); Zhang, P.X. [National Engineering Laboratory for Superconducting Materials (NELSM), Western Superconducting Technologies (WST) Co. Ltd., Xi’an 710018 (China); Northwest Institute for Nonferrous Metal Research (NIN), Xi’an 710016 (China); Qi, M. [Northwest Institute for Nonferrous Metal Research (NIN), Xi’an 710016 (China); Liu, X.H.; Feng, Y. [National Engineering Laboratory for Superconducting Materials (NELSM), Western Superconducting Technologies (WST) Co. Ltd., Xi’an 710018 (China); Chen, Y.L.; Zhao, Y. [Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Superconductivity and New Energy R& D Center, Southwest Jiaotong University (SWJTU), Chengdu 610031 (China)

    2015-06-15

    Highlights: • Nb{sub 3}Al superconducting wires with Cu-matrix and different filament numbers were prepared by the jelly-roll method. • The length of 18-cores Nb{sub 3}Al superconducting wire reaches 100 m without any breakage and intermediate anneal. • This wire has the uniform filament-shapes and fine long-wire homogeneity. • This Nb{sub 3}Al long wire has the T{sub c} of 13.4 K and J{sub c} of 4.7 × 10{sup 4} A/cm{sup 2} at 4.2 K and 12 T. - Abstract: With extremely high critical current density (J{sub c}) and excellent strain tolerance, Nb{sub 3}Al superconductor is considered as an alternative to Nb{sub 3}Sn for application of high-field magnets. However, owing to their complex structure, Nb{sub 3}Al superconducting wires can hardly meet the requirement of engineering application at present. In this work, a novel simple-structured Nb{sub 3}Al superconducting wires with Cu-matrix and different filament numbers were prepared by the conventional jelly-roll method, as well as a heat-treatment of 800–850 °C for 20–50 h. The results show that a 18-filament superconducting wire with length longer than 100 m can be successfully prepared by this method, and also this Nb{sub 3}Al long wire has the T{sub c} of 13.4 K and J{sub c} of 4.7 × 10{sup 4} A/cm{sup 2} at 4.2 K and 12 T. These suggest that with further optimization, the simple-structured Nb{sub 3}Al superconducting wires are very promising to fabricate the km-grade long wires to meet the requirement of engineering application.

  9. Superconducting electronics

    NARCIS (Netherlands)

    Rogalla, Horst

    1994-01-01

    During the last decades superconducting electronics has been the most prominent area of research for small scale applications of superconductivity. It has experienced quite a stormy development, from individual low frequency devices to devices with high integration density and pico second switching

  10. Th-substituted SmFeAsO: Structural details and superconductivity with Tc above 50 K

    Science.gov (United States)

    Zhigadlo, N. D.; Katrych, S.; Weyeneth, S.; Puzniak, R.; Moll, P. J. W.; Bukowski, Z.; Karpinski, J.; Keller, H.; Batlogg, B.

    2010-08-01

    We report structural, magnetic, and transport properties of polycrystalline samples and single crystals of superconducting Sm1-xThxFeAsO with maximal Tc above 50 K, prepared under high pressure. Bulk superconducting samples do not undergo a structural phase transition from tetragonal to orthorhombic symmetry at low temperatures. The unit-cell parameters a and c shrink with Th substitution and the fractional atomic coordinate of the As site zAs remains almost unchanged while that of Sm/Th zSm/Th increases. Upon warming from 5 to 295 K the increase in the FeAs layer thickness is dominant, while the changes in the other structural building blocks are minor, and they compensate each other, since the As-Sm/Th distance contracts by about the same amount as the O-Sm/Th expands. The polycrystalline and single-crystalline samples are characterized by a full diamagnetic response in low magnetic field, by a high intergrain critical current density for polycrystalline samples, and by a critical current density on the order of 8×105A/cm2 for single crystals at 2 K in fields up to 7 T. The magnetic penetration depth anisotropy γλ increases with decreasing temperature, in a similar way to that of SmFeAsO1-xFy single crystals. The upper critical field estimated from resistance measurements is anisotropic with slopes of ˜5.4T/K ( H∥ab plane) and ˜2.7T/K ( H∥c axis), at temperatures sufficiently far below Tc . The low-temperature upper critical field anisotropy γH is in the range of ˜2 , consistent with the tendency of a decreasing γH with decreasing temperature, previously reported for SmFeAsO1-xFy single crystals.

  11. Impact of the electronic band structure in high-harmonic generation spectra of solids

    CERN Document Server

    Tancogne-Dejean, Nicolas; Kärtner, Franz X; Rubio, Angel

    2016-01-01

    An accurate analytic model describing high-harmonic generation (HHG) in solids is derived. Extensive first-principles simulations within a time-dependent density-functional framework corroborate the conclusions of the model. Our results reveal that: (i) the emitted HHG spectra are highly anisotropic and laser-polarization dependent even for cubic crystals, (ii) the harmonic emission is enhanced by the inhomogeneity of the electron-nuclei potential, the yield is increased for heavier atoms, and (iii) the cutoff photon energy is driver-wavelength independent. Moreover, we show that it is possible to predict the laser polarization for optimal HHG in bulk crystals solely from the knowledge of their electronic band structure. Our results pave the way to better control and optimize HHG in solids by engineering their band structure.

  12. Growth, Band Structure and Optical Properties of LiSrBO3 Crystal

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The bulk crystal of LiSrBO3(8.39 g) with a size of 21mm × 20mm × 15mm was grown by high temperature solution growth method. The relationship between growth habit and crystal structure was discussed. The transmission spectrum shows an UV absorption edge at about 300 nm. The melting temperature of this crystal was determined to be 942 ℃ by DTA-TG measurement. The band structure of the LiSrBO3 crystal was studied by means of the first principle method. An indirect band gap was found to be about 4.0 eV, and a low dielectric constant was estimated to be about 1.9 in terms of theoretical results.

  13. Deformed configurations, band structures and spectroscopic properties of = 50 Ge and Se nuclei

    Indian Academy of Sciences (India)

    S K Ghorui; C R Praharaj

    2014-04-01

    The deformed configurations and rotational band structures in =50 Ge and Se nuclei are studied by deformed Hartree–Fock with quadrupole constraint and angular momentum projection. Apart from the `almost’ spherical HF solution, a well-deformed configuration occurs at low excitation. A deformed well-mixed = 1/2+ neutron orbit comes down in energy (from the shell above = 50) to break the = 50 spherical shell closure. A = 7− isomer is predicted in 84Se at fairly low excitation energy. At higher excitation energies (8 MeV), a deformed band with = 7/2+–1/2− (based on $h_{11/2}$) neutron 1p–1h excitation, for 82Ge and 84Se, is shown in our calculation. Our study gives insight into possible deformed structures at spherical shell closure.

  14. Band structure and optical properties of amber studied by first principles

    Energy Technology Data Exchange (ETDEWEB)

    Rao, Zhi-Fan, E-mail: raozhifan@163.com [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China); Zhou, Rong-Feng [Analysis and Testing Center of Yunnan, Kunming University of Science and Technology, Kunming 650093 (China)

    2013-03-01

    The band structure and density of states of amber is studied by the first principles calculation based on density of functional theory. The complex structure of amber has 214 atoms and the band gap is 5.0 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The optical properties' results show that the reflectivity is low, and the refractive index is 1.65 in visible light range. The highest absorption coefficient peak is at 172 nm and another higher peak is at 136 nm. These convince that the amber would have a pretty sheen and that amber is a good and suitable crystal for jewelry and ornaments.

  15. Evidence of a structural phase transition in superconducting SmFeAsO1-xFx from 19F NMR

    Science.gov (United States)

    Majumder, M.; Ghoshray, K.; Mazumdar, C.; Poddar, A.; Ghoshray, A.; Berardan, D.; Dragoe, N.

    2013-01-01

    We report resistivity, magnetization and 19F NMR results in a polycrystalline sample of SmFeAsO0.86F0.14. The resistivity and magnetization data show a sharp drop at 48 K indicating a superconducting transition. The nuclear spin-lattice rate (1/T1) and spin-spin relaxation rate (1/T2) clearly show the existence of a structural phase transition near 163 K in the sample, which also undergoes a superconducting transition. This finding creates interest in exploring whether this is unique for Sm based systems or is also present in other rare-earth based 1111 superconductors.

  16. Short pulse equations and localized structures in frequency band gaps of nonlinear metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Tsitsas, N.L. [School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Zografos, Athens 15773 (Greece); Horikis, T.P. [Department of Mathematics, University of Ioannina, Ioannina 45110 (Greece); Shen, Y.; Kevrekidis, P.G.; Whitaker, N. [Department of Mathematics and Statistics, University of Massachusetts, Amherst, MA 01003-4515 (United States); Frantzeskakis, D.J., E-mail: dfrantz@phys.uoa.g [Department of Physics, University of Athens, Panepistimiopolis, Zografos, Athens 157 84 (Greece)

    2010-03-01

    We consider short pulse propagation in nonlinear metamaterials characterized by a weak Kerr-type nonlinearity in their dielectric response. Two short-pulse equations (SPEs) are derived for the high- and low-frequency 'band gaps' (where linear electromagnetic waves are evanescent) with linear effective permittivity epsilon<0 and permeability mu>0. The structure of the solutions of the SPEs is also briefly discussed, and connections with the soliton solutions of the nonlinear Schroedinger equation are made.

  17. Band structure and Bloch states in birefringent 1D magnetophotonic crystals: An analytical approach

    CERN Document Server

    Lévy, M; Levy, Miguel; Jalali, Amir A

    2007-01-01

    An analytical formulation for the band structure and Bloch modes in elliptically birefringent magnetophotonic crystals is presented. The model incorporates both the effects of gyrotropy and linear birefringence generally present in magneto-optic thin film devices. Full analytical expressions are obtained for the dispersion relation and Bloch modes in a layered stack photonic crystal and their properties are analyzed. It is shown that other models recently discussed in the literature are contained as special limiting cases of the formulation presented herein.

  18. Dispersion characteristics of a slow wave structure with a modified photonic band gap

    Institute of Scientific and Technical Information of China (English)

    Gao Xi; Yang Zi-Qiang; Cao Wei-Ping; Jiang Yan-Nan

    2011-01-01

    This paper studies the dispersion characteristics of a modified photonic band-gap slow-wave structure with an open boundary by simulation and experiment. A mode launcher with a wheel radiator and a coupling probe is presented to excite a pure TM01-like mode. The cold test and simulation results show that the TM01-like mode is effectively excited and no parasitic modes appear. The dispersion characteristics obtained from the cold test are in good agreement with the calculated results.

  19. Band structures tunability of bulk 2D phononic crystals made of magneto-elastic materials

    Directory of Open Access Journals (Sweden)

    J. O. Vasseur

    2011-12-01

    Full Text Available The feasibility of contactless tunability of the band structure of two-dimensional phononic crystals is demonstrated by employing magnetostrictive materials and applying an external magnetic field. The influence of the amplitude and of the orientation with respect to the inclusion axis of the applied magnetic field are studied in details. Applications to tunable selective frequency filters with switching functionnality and to reconfigurable wave-guides and demultiplexing devices are then discussed.

  20. Superconducting Fullerene Nanowhiskers

    Directory of Open Access Journals (Sweden)

    Yoshihiko Takano

    2012-04-01

    Full Text Available We synthesized superconducting fullerene nanowhiskers (C60NWs by potassium (K intercalation. They showed large superconducting volume fractions, as high as 80%. The superconducting transition temperature at 17 K was independent of the K content (x in the range between 1.6 and 6.0 in K-doped C60 nanowhiskers (KxC60NWs, while the superconducting volume fractions changed with x. The highest shielding fraction of a full shielding volume was observed in the material of K3.3C60NW by heating at 200 °C. On the other hand, that of a K-doped fullerene (K-C60 crystal was less than 1%. We report the superconducting behaviors of our newly synthesized KxC60NWs in comparison to those of KxC60 crystals, which show superconductivity at 19 K in K3C60. The lattice structures are also discussed, based on the x-ray diffraction (XRD analyses.

  1. Structural and superconducting properties of La2−xNdxCuO4+y (0≤x≤0.5) prepared by room temperature chemical oxidation

    DEFF Research Database (Denmark)

    Rial, C.; Morán, E.; Alario-Franco, M.A.;

    1997-01-01

    The systematic characterization of the structural and superconducting properties of room temperature chemically oxidized T/O La2-xNdxCuO4+y (0 less than or equal to x less than or equal to 0.5) has been performed by neutron powder diffraction and magnetic susceptibility measurements. Similarities...

  2. Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (Ca(x)Sr(1-x))₃Rh₄Sn₁₃.

    Science.gov (United States)

    Yu, Wing Chi; Cheung, Yiu Wing; Saines, Paul J; Imai, Masaki; Matsumoto, Takuya; Michioka, Chishiro; Yoshimura, Kazuyoshi; Goh, Swee K

    2015-11-13

    The family of the superconducting quasiskutterudites (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) features a structural quantum critical point at x(c)=0.9, around which a dome-shaped variation of the superconducting transition temperature T(c) is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching x(c), which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2Δ/k(B)T(c) and ΔC/γT(c) beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.

  3. Superconductivity in graphite intercalation compounds

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Robert P. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Weller, Thomas E.; Howard, Christopher A. [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom); Dean, Mark P.M. [Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973 (United States); Rahnejat, Kaveh C. [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom); Saxena, Siddharth S. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Ellerby, Mark, E-mail: mark.ellerby@ucl.ac.uk [Department of Physics & Astronomy, University College of London, Gower Street, London WCIE 6BT (United Kingdom)

    2015-07-15

    Highlights: • Historical background of graphite intercalates. • Superconductivity in graphite intercalates and its place in the field of superconductivity. • Recent developments. • Relevant modeling of superconductivity in graphite intercalates. • Interpretations that pertain and questions that remain. - Abstract: The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s (Dresselhaus and Dresselhaus, 1981; Enoki et al., 2003). This paper recontextualizes the field in light of the discovery of superconductivity in CaC{sub 6} and YbC{sub 6} in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how these relate to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity, and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.

  4. Structure and superconductivity in (Bi(0.35)Cu(0.65))Sr2YCu2O7 and related materials

    Science.gov (United States)

    Jennings, R. A.; Williams, S. P.; Greaves, C.

    1995-01-01

    The recently reported (Bi/Cu)Sr2YCu2O7 phase has been studied by time of flight powder neutron diffraction. The proposed 1212 structure has been confirmed and refinements have shown the oxygen in the (Bi/Cu)O layer is displaced by 0.78 A from the ideal (1/2,1/2,0) site (P4/mmm space group) along /100/. Bond Valence Sum calculations have suggested oxidation states of Bi(5+) and Cu(2+) for the cations in the (Bi/Cu)O layers. The material is non-superconducting and all attempts to induce superconductivity have been unsuccessful. Work on the related material (Ce/Cu)Sr2YCu2O7 has shown the ideal Ce content to be 0.5 Ce per formula unit. The introduction of Ba (10%) onto the Sr site dramatically increases phase stability and also induces superconductivity (62 K).

  5. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study.

    Science.gov (United States)

    Zhong, C; Zhang, H; Cao, Q P; Wang, X D; Zhang, D X; Ramamurty, U; Jiang, J Z

    2016-08-02

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and "liquid-like" regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested.

  6. Banding and electronic structures of metal azides——Sensitivity and conductivity

    Institute of Scientific and Technical Information of China (English)

    肖鹤鸣; 李永富

    1995-01-01

    By using both DV-Xα and EH-CO methods, the calculation studies of the structure-property relationships of a series of metal azides, of their clusters’ electronic structures in ground and excited states, of their systems with cation vacancy and the doped Pb(N3)2, as well as their crystal band structures have been conducted. The results show that the sensitivity of ionic-type metal azides varies with the degree of difficulty of electronic transition of the losing charge on N3. A metal azide with cation vacancies has a greater sensitivity than the perfect one. When doped with monovalent metal ions, lead azide’s sensitivity increased; when with trivalent ones, its sensitivity decreased; when with divalent ones, little of it changed. Compared with heavy metal azides. an alkali metal azide has a larger band gap, a smaller band width and a greater transition energy of frontier electron with a smaller amount of losing charge on N3, and thus has lower sensitivity and conductivity than heavy metal azides.

  7. Robust topology optimization of three-dimensional photonic-crystal band-gap structures.

    Science.gov (United States)

    Men, H; Lee, K Y K; Freund, R M; Peraire, J; Johnson, S G

    2014-09-22

    We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for robust topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors.

  8. Anticorrelation between polar lattice instability and superconductivity in the Weyl semimetal candidate MoTe2

    Science.gov (United States)

    Takahashi, H.; Akiba, T.; Imura, K.; Shiino, T.; Deguchi, K.; Sato, N. K.; Sakai, H.; Bahramy, M. S.; Ishiwata, S.

    2017-03-01

    The relation between the polar structural instability and superconductivity in a Weyl semimetal candidate MoTe2 has been clarified by finely controlled physical and chemical pressure. The physical pressure as well as the chemical pressure, i.e., the Se substitution for Te, enhances the superconducting transition temperature Tc at around the critical pressure where the polar structure transition disappears. From the heat capacity and thermopower measurements, we ascribe the significant enhancement of Tc at the critical pressure to a subtle modification of the phonon dispersion or the semimetallic band structure upon the polar-to-nonpolar transition. On the other hand, the physical pressure, which strongly reduces the interlayer distance, is more effective on the suppression of the polar structural transition and the enhancement of Tc as compared with the chemical pressure, which emphasizes the importance of the interlayer coupling on the structural and superconducting instability in MoTe2.

  9. Phase separation in iron chalcogenide superconductor Rb0.8+xFe1.6+ySe2 as seen by Raman light scattering and band structure calculations

    Science.gov (United States)

    Pashkevich, Yu.; Gnezdilov, V.; Lemmens, P.; Shevtsova, T.; Gusev, A.; Lamonova, K.; Wulferding, D.; Gnatchenko, S.; Pomjakushina, E.; Conder, K.

    2016-06-01

    We report Raman light scattering in the phase separated superconducting single crystal Rb0.77Fe1.61Se2 with Tc = 32 K over a wide temperature region 3-500 K. The observed phonon lines from the majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN = 525 K demonstrate modest anomalies in the frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed RbδFe2Se2 (122) conductive phase. The superconducting gap with d x 2 - y 2 symmetry has been detected in our spectra. In the range 0-600 cm-1 we observe a weak but highly polarized B1g-type background which becomes well-structured upon cooling. A possible magnetic or multiorbital origin of this background is discussed. We argue that the phase separation in M0.8+xFe1.6+ySe2 is of pure magnetic origin. It occurs below the Néel temperature when the magnetic moment of iron reaches a critical value. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab initio spin-polarized band structure calculations we demonstrate that the compressed vacancy ordered Rb2Fe4Se5 phase can be conductive and therefore may serve as a protective interface spacer between the purely metallic RbδFe2Se2 phase and the insulating Rb2Fe4Se5 phase providing percolative Josephson-junction like superconductivity all throughout of Rb0.8+xFe1.6+ySe2. Our lattice dynamics calculations show significant differences in the phonon spectra of the conductive and insulating Rb2Fe4Se5 phases.

  10. Probing Atomic Structure and Majorana Wavefunctions in Mono-Atomic Fe-chains on Superconducting Pb-Surface

    CERN Document Server

    Pawlak, Remy; Klinovaja, Jelena; Meier, Tobias; Kawai, Shigeki; Glatzel, Thilo; Loss, Daniel; Meyer, Ernst

    2015-01-01

    Motivated by the striking promise of quantum computation, Majorana bound states (MBSs) in solid-state systems have attracted wide attention in recent years. In particular, the wavefunction localization of MBSs is a key feature and crucial for their future implementation as qubits. Here, we investigate the spatial and electronic characteristics of topological superconducting chains of iron atoms on the surface of Pb(110) by combining scanning tunneling microscopy (STM) and atomic force microscopy (AFM). We demonstrate that the Fe chains are mono-atomic, structured in a linear fashion, and exhibit zero-bias conductance peaks at their ends which we interprete as signature for a Majorana bound state. Spatially resolved conductance maps of the atomic chains reveal that the MBSs are well localized at the chain ends (below 25 nm), with two localization lengths as predicted by theory. Our observation lends strong support to use MBSs in Fe chains as qubits for quantum computing devices.

  11. Hyper-Temporal C-Band SAR for Baseline Woody Structural Assessments in Deciduous Savannas

    Directory of Open Access Journals (Sweden)

    Russell Main

    2016-08-01

    Full Text Available Savanna ecosystems and their woody vegetation provide valuable resources and ecosystem services. Locally calibrated and cost effective estimates of these resources are required in order to satisfy commitments to monitor and manage change within them. Baseline maps of woody resources are important for analyzing change over time. Freely available, and highly repetitive, C-band data has the potential to be a viable alternative to high-resolution commercial SAR imagery (e.g., RADARSAT-2, ALOS2 in generating large-scale woody resources maps. Using airborne LiDAR as calibration, we investigated the relationships between hyper-temporal C-band ASAR data and woody structural parameters, namely total canopy cover (TCC and total canopy volume (TCV, in a deciduous savanna environment. Results showed that: the temporal filter reduced image variance; the random forest model out-performed the linear model; while the TCV metric consistently showed marginally higher accuracies than the TCC metric. Combinations of between 6 and 10 images could produce results comparable to high resolution commercial (C- & L-band SAR imagery. The approach showed promise for producing a regional scale, locally calibrated, baseline maps for the management of deciduous savanna resources, and lay a foundation for monitoring using time series of data from newer C-band SAR sensors (e.g., Sentinel1.

  12. A Ku-band magnetically insulated transmission line oscillator with overmoded slow-wave-structure

    Science.gov (United States)

    Jiang, Tao; He, Jun-Tao; Zhang, Jian-De; Li, Zhi-Qiang; Ling, Jun-Pu

    2016-12-01

    In order to enhance the power capacity, an improved Ku-band magnetically insulated transmission line oscillator (MILO) with overmoded slow-wave-structure (SWS) is proposed and investigated numerically and experimentally. The analysis of the dispersion relationship and the resonant curve of the cold test indicate that the device can operate at the near π mode of the TM01 mode, which is useful for mode selection and control. In the particle simulation, the improved Ku-band MILO generates a microwave with a power of 1.5 GW and a frequency of 12.3 GHz under an input voltage of 480 kV and input current of 42 kA. Finally, experimental investigation of the improved Ku-band MILO is carried out. A high-power microwave (HPM) with an average power of 800 MW, a frequency of 12.35 GHz, and pulse width of 35 ns is generated under a diode voltage of 500 kV and beam current of 43 kA. The consistency between the experimental and simulated far-field radiation pattern confirms that the operating mode of the improved Ku-band MILO is well controlled in π mode of the TM01 mode. Project supported partly by the National Natural Science Foundation of China (Grant No. 61171021).

  13. Experimental validation of superconducting quantum interference device sensors for electromagnetic scattering in geologic structures

    Energy Technology Data Exchange (ETDEWEB)

    Krauss, R.H. Jr.; Flynn, E.; Ruminer, P. [and others

    1997-10-01

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This project has supported the collaborative development with Sandia National Laboratories (SNL) and the University of New Mexico (UNM) of two critical components for a hand-held low-field magnetic sensor based on superconducting quantum interference device (SQUID) sensor technology. The two components are a digital signal processing (DSP) algorithm for background noise rejection and a small hand-held dewar cooled by a cryocooler. A hand-held sensor has been designed and fabricated for detection of extremely weak magnetic fields in unshielded environments. The sensor is capable of measuring weak magnetic fields in unshielded environments and has multiple applications. We have chosen to pursue battlefield medicine as the highest probability near-term application because of stated needs of several agencies.

  14. Fabrication of the CERN/PSI/ST X-Band accelerating structures

    CERN Document Server

    Dehler, Micha; Gudkov, Dmitry; Lebet, Serge; Riddone, Germana; Shi, Jiaru; Citterio, Alessandro; Zennaro, Riccardo; D'Auria, Gerardo; Serpico, Claudio

    2011-01-01

    In a collaboration between CERN, PSI and Sincrotrone Trieste (ST), a multi- purpose X-band accelerating structure has been designed and fabricated, used for high gradients tests in the CLIC structure testing program and in the FEL projects of PSI and ST. The structure has 72 cells with a phase advance of 5 pi/6 and includes upstream and down-stream wakefield monitors to measure the beam alignment. The SLAC mode launcher design is used to feed it with RF power. Following the CERN fabrication procedures for high-gradient structure, diffusion bonding and brazing in hydrogen atmosphere is used to assemble the cells. After tuning, a vacuum bakeout is required before the feedthroughs for the wake field monitors are welded in as a last step. We describe the experiences gained in finishing the first two structures out of a series of four and present the results from the RF tuning and low level RF tests.

  15. Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure.

    Science.gov (United States)

    Simakov, Evgenya I; Arsenyev, Sergey A; Buechler, Cynthia E; Edwards, Randall L; Romero, William P; Conde, Manoel; Ha, Gwanghui; Power, John G; Wisniewski, Eric E; Jing, Chunguang

    2016-02-12

    We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic-band-gap (PBG) accelerating structure at 11.700 GHz. It has been long recognized that PBG structures have the potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. We conducted an experiment at the Argonne Wakefield Accelerator test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test.

  16. Band structure calculation of GaSe-based nanostructures using empirical pseudopotential method

    Science.gov (United States)

    Osadchy, A. V.; Volotovskiy, S. G.; Obraztsova, E. D.; Savin, V. V.; Golovashkin, D. L.

    2016-08-01

    In this paper we present the results of band structure computer simulation of GaSe- based nanostructures using the empirical pseudopotential method. Calculations were performed using a specially developed software that allows performing simulations using cluster computing. Application of this method significantly reduces the demands on computing resources compared to traditional approaches based on ab-initio techniques and provides receiving the adequate comparable results. The use of cluster computing allows to obtain information for structures that require an explicit account of a significant number of atoms, such as quantum dots and quantum pillars.

  17. Extended Hückel theory for carbon nanotubes: band structure and transport properties.

    Science.gov (United States)

    Zienert, Andreas; Schuster, Jörg; Gessner, Thomas

    2013-05-02

    Extended Hückel theory (EHT) is a well established method for the description of the electronic structure of molecules and solids. In this article, we present a set of extended Hückel parameters for carbon nanotubes (CNTs), obtained by fitting the ab initio band structure of the (6,0) CNT. The new parameters are highly transferable to different types of CNTs. To demonstrate the versatility of the approach, we perform self-consistent EHT-based electron transport calculations for finite length CNTs with metal electrodes.

  18. Quasiparticle band structure for the Hubbard systems: Application to. alpha. -CeAl sub 2

    Energy Technology Data Exchange (ETDEWEB)

    Costa-Quintana, J.; Lopez-Aguilar, F. (Departamento de Fisica, Grupo de Electromagnetismo, Universidad Autonoma de Barcelona, Bellaterra, E-08193 Barcelona, Spain (ES)); Balle, S. (Departament de Fisica, Universitat de les Illes Balears, E-07071 Palma de Mallorca, Spain (ES)); Salvador, R. (Control Data Corporation, TALLAHASSEE, FL (USA) Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida 32306-4052 (USA))

    1990-04-01

    A self-energy formalism for determining the quasiparticle band structure of the Hubbard systems is deduced. The self-energy is obtained from the dynamically screened Coulomb interaction whose bare value is the correlation energy {ital U}. A method for integrating the Schroedingerlike equation with the self-energy operator is given. The method is applied to the cubic Laves phase of {alpha}-CeAl{sub 2} because it is a clear Hubbard system with a very complex electronic structure and, moreover, this system provides us with sufficient experimental data for testing our method.

  19. DFT Study of Effects of Potassium Doping on Band Structure of Crystalline Cuprous Azide

    Institute of Scientific and Technical Information of China (English)

    ZHU,Wei-Hua; ZHANG,Xiao-Wen; WEI,Tao; XIAO,He-Ming

    2008-01-01

    The structure and defect formation energies of the K-doped CuN3 were studied using density functional theory within the generalized gradient approximation. The results show that the K-doping breaks the azide symmetry and causes asymmetric atomic displacement. As the K-doping level increases, the band gap of the doped system gradually increases. The K impurity is easily incorporated into the crystal thermodynamically. The Cu vacancy is easily created thermodynamically and the K impurity can serve as nucleation centers for vacancy clustering. Finally the effects of K-doping concentrations on the sensitivity of CuN3 were understood based on electronic structures.

  20. Structure-Band Gap Relationships in Hexagonal Polytypes and Low-Dimensional Structures of Hybrid Tin Iodide Perovskites.

    Science.gov (United States)

    Stoumpos, Constantinos C; Mao, Lingling; Malliakas, Christos D; Kanatzidis, Mercouri G

    2017-01-03

    The present study deals with the structural characterization and classification of the novel compounds 1-8 into perovskite subclasses and proceeds in extracting the structure-band gap relationships between them. The compounds were obtained from the employment of small, 3-5-atom-wide organic ammonium ions seeking to discover new perovskite-like compounds. The compounds reported here adopt unique or rare structure types akin to the prototype structure perovskite. When trimethylammonium (TMA) was employed, we obtained TMASnI3 (1), which is our reference compound for a "perovskitoid" structure of face-sharing octahedra. The compounds EASnI3 (2b), GASnI3 (3a), ACASnI3 (4), and IMSnI3 (5) obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium (ACA), and imidazolium (IM) cations, respectively, represent the first entries of the so-called "hexagonal perovskite polytypes" in the hybrid halide perovskite library. The hexagonal perovskites define a new family of hybrid halide perovskites with a crystal structure that emerges from a blend of corner- and face-sharing octahedral connections in various proportions. The small organic cations can also stabilize a second structural type characterized by a crystal lattice with reduced dimensionality. These compounds include the two-dimensional (2D) perovskites GA2SnI4 (3b) and IPA3Sn2I7 (6b) and the one-dimensional (1D) perovskite IPA3SnI5 (6a). The known 2D perovskite BA2MASn2I7 (7) and the related all-inorganic 1D perovskite "RbSnF2I" (8) have also been synthesized. All compounds have been identified as medium-to-wide-band-gap semiconductors in the range of Eg = 1.90-2.40 eV, with the band gap progressively decreasing with increased corner-sharing functionality and increased torsion angle in the octahedral connectivity.

  1. Tunable mechanical monolithic sensors for large band low frequency monitoring and characterization of sites and structures

    Science.gov (United States)

    Barone, F.; Giordano, G.; Acernese, F.; Romano, R.

    2016-10-01

    Among the different mechanical architectures present in literature, the Watts linkage is one of the most promising ones for the implementation of a new class of mechanical accelerometers (horizontal, vertical and angular). In this paper, we present monolithic implementations of uniaxial and triaxial mechanical seismometers and accelerometers based on the UNISA Folded Pendulum mechanical configuration, optimized for low frequency characterization of sites (including underground sites) and structures as inertial sensor (seismometer). This mechanical architecture allows the design and implementation of very large band monolithic sensors (10-7Hz 102 Hz), whose sensitivities for the most common applications are defined by the noise introduced by their readouts (e.g. ¡ 10-12 m/sqrt(Hz) with classical LVDT readouts). These unique features, coupled other relevant properties like scalability, compactness, lightness, high directivity, frequency tunability (typical resonance frequencies in the band 10-1 Hz 102 Hz), very high immunity to environmental noises and low cost make this class of sensors very effective for the implementation of uniaxial (horizontal and/or vertical) and triaxial seismometers and accelerometers for ground, space and underwater applications, including UHV and cryogenics ones. Typical applications of this class of monolithic sensors are in the field of earthquake engineering, seismology, geophysics, civil engineering, characterization of sites (including underground sites), structures (e.g. buildings, bridges, historical monuments), and, in general, in all applications requiring large band-low frequency performances coupled with high sensitivities and compactness.

  2. Crystal structure, conformation, vibration and optical band gap analysis of bis[ rac-propranolol nitrate

    Science.gov (United States)

    Franklin, S.; Balasubramanian, T.; Nehru, K.; Kim, Youngmee

    2009-06-01

    The crystal structure of the title rac-propranolol salt, CHNO2+·NO3-, consists of two protonated propranolol residues and nitrate anions. Three virtually flat fragments, characteristics of most of the β-adrenolytics with oxy-methylene bridge are present in both the cations (A and B). The plane of the propranolol chain is twisted with respect to the plane of the aromatic ring in both the cations. Present study investigates the conformation and hydrogen bonding interactions, which play an important role in biological functions. A gauche conformation is observed for the oxo-methylene bridge of cation A, while a trans conformation prevails in cation B. These conformations are found in majority of β-blockers. Presence of twenty intermolecular hydrogen bonds mediating through the anions stabilizes the crystal packing. Vibration analysis and earlier theoretical predictions complement the structure analysed. From the UV-Vis spectral analysis for the crystal, the optical band gap is found to be Eg = 5.12 eV, where as the chloride salt has Eg = 3.81 eV. The increase in the band gap may be attributed by the increase in the number of intermolecular hydrogen bonds. Good optical transmittance in the entire visible region and the direct band gap property suggest that it is a suitable candidate for optical applications in UV region.

  3. Band structure and spin texture of Bi2Se3 3 d ferromagnetic metal interface

    Science.gov (United States)

    Zhang, Jia; Velev, Julian P.; Dang, Xiaoqian; Tsymbal, Evgeny Y.

    2016-07-01

    The spin-helical surface states in a three-dimensional topological insulator (TI), such as Bi2Se3 , are predicted to have superior efficiency in converting charge current into spin polarization. This property is said to be responsible for the giant spin-orbit torques observed in ferromagnetic metal/TI structures. In this work, using first-principles and model tight-binding calculations, we investigate the interface between the topological insulator Bi2Se3 and 3 d -transition ferromagnetic metals Ni and Co. We find that the difference in the work functions of the topological insulator and the ferromagnetic metals shift the topological surface states down about 0.5 eV below the Fermi energy where the hybridization of these surface states with the metal bands destroys their helical spin structure. The band alignment of Bi2Se3 and Ni (Co) places the Fermi energy far in the conduction band of bulk Bi2Se3 , where the spin of the carriers is aligned with the magnetization in the metal. Our results indicate that the topological surface states are unlikely to be responsible for the huge spin-orbit torque effect observed experimentally in these systems.

  4. Band Structure and Optical Properties of Kesterite Type Compounds: first principle calculations

    Science.gov (United States)

    Palaz, S.; Unver, H.; Ugur, G.; Mamedov, A. M.; Ozbay, E.

    2017-02-01

    In present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated.

  5. Superconductivity of metallic boron in MgB2.

    Science.gov (United States)

    Kortus, J; Mazin, I I; Belashchenko, K D; Antropov, V P; Boyer, L L

    2001-05-14

    Boron in MgB2 forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate via zone-center frozen phonon calculations to be between 300 and 700 cm(-1), this produces a high critical temperature, consistent with recent experiments. Thus MgB2 can be viewed as an analog of the long sought, but still hypothetical, superconducting metallic hydrogen.

  6. The effect of spin-orbit coupling in band structure of few-layer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Sahdan, Muhammad Fauzi, E-mail: sahdan89@yahoo.co.id; Darma, Yudi, E-mail: sahdan89@yahoo.co.id [Department of Physics, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung 40132 (Indonesia)

    2014-03-24

    Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. This can be happened due to spin-orbit coupling and time-reversal symmetry. Moreover, the edge current flows through their edge or surface depends on its spin orientation and also it is robust against non-magnetic impurities. Therefore, topological insulators are predicted to be useful ranging from spintronics to quantum computation. Graphene was first predicted to be the precursor of topological insulator by Kane-Mele. They developed a Hamiltonian model to describe the gap opening in graphene. In this work, we investigate the band structure of few-layer graphene by using this model with analytical approach. The results of our calculations show that the gap opening occurs at K and K’ point, not only in single layer, but also in bilayer and trilayer graphene.

  7. InN/GaN Superlattices: Band Structures and Their Pressure Dependence

    DEFF Research Database (Denmark)

    Gorczyca, Iza; Suski, Tadek; Staszczak, Grzegorz;

    2013-01-01

    with one monolayer of InN and 40 monolayers of GaN. The results are compared with calculations performed for different types of superlattices: InN/GaN, InGaN/GaN, and InN/InGaN/GaN with single monolayers of InN and/or InGaN. The superlattices are simulated by band structure calculations based on the local......Creation of short-period InN/GaN superlattices is one of the possible ways of conducting band gap engineering in the green-blue range of the spectrum. The present paper reports results of photoluminescence experiments, including pressure effects, on a superlattice sample consisting of unit cells...

  8. Investigation of the Band Structure of Graphene-Based Plasmonic Photonic Crystals

    Directory of Open Access Journals (Sweden)

    Pingping Qiu

    2016-09-01

    Full Text Available In this paper, one-dimensional (1D and two-dimensional (2D graphene-based plasmonic photonic crystals (PhCs are proposed. The band structures and density of states (DOS have been numerically investigated. Photonic band gaps (PBGs are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC.

  9. Impurity effects on the band structure of one-dimensional photonic crystals: experiment and theory

    Energy Technology Data Exchange (ETDEWEB)

    Luna-Acosta, G A [Instituto de Fisica, BUAP Apartado Postal J-48, 72570 Puebla (Mexico); Schanze, H; Kuhl, U; Stoeckmann, H-J [Fachbereich Physik der Philipps-Universitaet Marburg, Renthof 5, D-35032 (Germany)], E-mail: gluna@sirio.ifuap.buap.mx

    2008-04-15

    We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one-dimensional (1D) obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e.g. interstitial and substitutional) and show that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulae, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penney model.

  10. Fermi surface and band structure of BiPd from ARPES studies

    Science.gov (United States)

    Lohani, H.; Mishra, P.; Gupta, Anurag; Awana, V. P. S.; Sekhar, B. R.

    2017-03-01

    We present a detailed electronic structure study of the non-centrosymmetric superconductor BiPd based on our angle resolved photoemission spectroscopy (ARPES) measurements and Density Functional Theory (DFT) based calculations. We observe a high intensity distribution on the Fermi surface (FS) of this compound resulting from various electron and hole like bands which are present in the vicinity of the Fermi energy (Ef). The near Ef states are primarily composed of Bi-6p with a little admixture of Pd-4dx2-y2/zy orbitals. There are various spin-orbit split bands involved in the crossing of Ef making a complex FS. The FS mainly consists of multi sheets of three dimensions which disfavor the nesting between different sheets of the FS. Our comprehensive study elucidates that BiPd could be a s-wave multiband superconductor.

  11. Direct observation of the band structure in bulk hexagonal boron nitride

    Science.gov (United States)

    Henck, Hugo; Pierucci, Debora; Fugallo, Giorgia; Avila, José; Cassabois, Guillaume; Dappe, Yannick J.; Silly, Mathieu G.; Chen, Chaoyu; Gil, Bernard; Gatti, Matteo; Sottile, Francesco; Sirotti, Fausto; Asensio, Maria C.; Ouerghi, Abdelkarim

    2017-02-01

    A promising route towards nanodevice applications relies on the association of graphene and transition metal dichalcogenides with hexagonal boron nitride (h -BN ). Due to its insulating nature, h -BN has emerged as a natural substrate and gate dielectric for graphene-based electronic devices. However, some fundamental properties of bulk h -BN remain obscure. For example, the band structure and the position of the Fermi level have not been experimentally resolved. Here, we report a direct observation of parabolic dispersions of h -BN crystals using high-resolution angle-resolved photoemission spectroscopy (ARPES). We find that h -BN exfoliation on epitaxial graphene enables overcoming the technical difficulties of using ARPES with insulating materials. We show trigonal warping of the intensity maps at constant energy. The valence-band maxima are located around the K points, 2.5 eV below the Fermi level, thus confirming the residual p -type character of typical h -BN .

  12. Investigation of the Band Structure of Graphene-Based Plasmonic Photonic Crystals

    Science.gov (United States)

    Qiu, Pingping; Qiu, Weibin; Lin, Zhili; Chen, Houbo; Tang, Yixin; Wang, Jia-Xian; Kan, Qiang; Pan, Jiao-Qing

    2016-01-01

    In this paper, one-dimensional (1D) and two-dimensional (2D) graphene-based plasmonic photonic crystals (PhCs) are proposed. The band structures and density of states (DOS) have been numerically investigated. Photonic band gaps (PBGs) are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC.

  13. The band structure of carbonmonoxide on 2-D Au islands on graphene

    KAUST Repository

    Katsiev, Khabiboulakh

    2014-06-01

    The dispersion of the occupied molecular orbitals of carbon monoxide adsorbed on Au 2D islands, vapor-deposited on graphene/Ru(0 0 0 1), is seen to be wave vector dependent, as revealed by angle-resolved photoemission. The band dispersion is similar to CO monolayers adsorbed on many single crystal metal surfaces. Thus not only are the adsorbed gold islands on graphene flat and crystalline, as evident in the dispersion of the Au d-states, but the CO molecular adlayer is both molecular and ordered as well. The experimental angle-resolved photoemission combined with model calculations of the occupied CO band structure, suggest that, in spite of being a very weakly bound adsorbate, the CO adlayer on Au 2D islands on graphene is strongly hybridized to the Au layer. . © 2014 Elsevier B.V. All rights reserved.

  14. Impurity effects on the band structure of one-dimensional photonic crystals: Experiment and theory

    CERN Document Server

    Luna-Acosta, G A; Kuhl, U; Stoeckmann, H -J

    2007-01-01

    We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one dimensional obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes, and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e. g. interstitial, substitutional) and shows that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulas, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penn...

  15. Compact Dual-Band Planar Inverted-e-Shaped Antenna Using Defected Ground Structure

    Directory of Open Access Journals (Sweden)

    Wen Piao Lin

    2014-01-01

    Full Text Available This paper presents a novel dual-band planar inverted-e-shaped antenna (PIEA using defected ground structure (DGS for Bluetooth and wireless local area network (WLAN applications. The PIEA can reduce electromagnetic interferences (EMIs and it is constructed on a compact printed circuit board (PCB size of 10 × 5 × 4 mm3. Experimental results indicate that the antenna with a compact meandered slit can improve the operating impedance matching and bandwidths at 2.4 and 5.5 GHz. The measured power gains at 2.4 and 5.5 GHz band are 1.99 and 3.71 dBi; antenna efficiencies are about 49.33% and 55.23%, respectively. Finally, the good performances of the proposed antenna can highly promote for mobile device applications.

  16. Dual Band and Beam-Steering Antennas Using Reconfigurable Feed on Sierpinski Structure

    Directory of Open Access Journals (Sweden)

    Seonghun Kang

    2015-01-01

    Full Text Available Fractal patch antennas based on the Sierpinski structure are studied in this paper. The antennas operate at dual bands (around 2 and 5 GHz and are designed to steer the beam directions at around 5 GHz band (the first harmonic. The antennas use reconfigurable triple feeds on the same antenna plane to have three beam directions. The same scale factor defines the geometrical self-similarity of the Sierpinski fractal. The proposed antennas are fabricated through three iterations from 1st order to 3rd order and utilize FR-4 (εr = 4.4 for the microwave substrate. The performances of the antennas, such as reflection coefficients and radiation patterns are verified by simulation and measurement. The results show that the properties of the proposed antennas in three orders are similar.

  17. Multiband frequency-reconfigurable antenna using metamaterial structure of electromagnetic band gap

    Science.gov (United States)

    Dewan, Raimi; Rahim, M. K. A.; Himdi, Mohamed; Hamid, M. R.; Majid, H. A.; Jalil, M. E.

    2017-01-01

    A metamaterial of electromagnetic band gap (EBG) is incorporated to an antenna for frequency reconfigurability is proposed. The EBG consists of two identical unit cells that provide multiple band gaps at 1.88-1.94, 2.25-2.44, 2.67-2.94, 3.52-3.54, and 5.04-5.70 GHz with different EBG configurations. Subsequently, the antenna is incorporated with EBG. The corresponding incorporated structure successfully achieves various reconfigurable frequencies at 1.60, 1.91, 2.41, 3.26, 2.87, 5.21, and 5.54 GHz. The antenna has the potential to be implemented for Bluetooth, Wi-Fi, WiMAX, LTE, and cognitive radio applications.

  18. HOM-Free Linear Accelerating Structure for e+ e- Linear Collider at C-Band

    CERN Document Server

    Kubo, K

    2003-01-01

    HOM-free linear acceleration structure using the choke mode cavity (damped cavity) is now under design for e sup + e sup - linear collider project at C-band frequency (5712 MHz). Since this structure shows powerful damping effect on most of all HOMs, there is no multibunch problem due to long range wakefields. The structure will be equipped with the microwave absorbers in each cells and also the in-line dummy load in the last few cells. The straightness tolerance for 1.8 m long structure is closer than 30 (micro)m for 25% emittance dilution limit, which can be achieved by standard machining and braising techniques. Since it has good vacuum pumping conductance through annular gaps in each cell, instabilities due to the interaction of beam with the residual-gas and ions can be minimized.

  19. Cohesive band structure of carbon nanotubes for applications in quantum transport.

    Science.gov (United States)

    Arora, Vijay K; Bhattacharyya, Arkaprava

    2013-11-21

    An integrated cohesive band structure of carbon nanotubes (CNTs) applicable to all chirality directions (n, m), starting from the Dirac cone of a graphene nanolayer in k-space, is demarcated, in direct contrast to dissimilar chiral and achiral versions in the published literature. The electron wave state of a CNT is quantized into one-dimensional (1-D) nanostructure with a wrapping mode, satisfying the boundary conditions from one Dirac K-point to an equivalent neighboring one with an identical phase and returning to the same K point. The repetitive rotation for an identical configuration with added band index (n-m)mod3, yields one metallic (M) with zero bandgap corresponding to (n-m)mod3 = 0, semiconducting state SC1 with (n-m)mod3 = 1 and SC2 with (n-m)mod3 = 2. The band gap and effective mass of SC2 state are twice as large as those of SC1 state. A broad-spectrum expression signifying the linear dependence of the effective mass on the bandgap is obtained. Both the Fermi energy and the intrinsic velocity limiting the current to the saturation level is calculated as a function of the carrier concentration. Limitations of the parabolic approximation are pointed out. Several new features of the band structure are acquired in a seamlessly unified mode for all CNTs, making it suitable for all-encompassing applications. Applications of the theory to high-field transport are advocated with an example of a metallic CNT, in agreement with experimental observations. The mechanism behind the breakdown of the linear current-voltage relation of Ohm's law and the associated surge in resistance are explained on the basis of the nonequilibrium Arora's distribution function (NEADF). These results are important for the performance evaluation and characterization of a variety of applications on CNT in modern nanoscale circuits and devices.

  20. Pressure-induced superconductivity in the giant Rashba system BiTeI

    Science.gov (United States)

    VanGennep, D.; Linscheid, A.; Jackson, D. E.; Weir, S. T.; Vohra, Y. K.; Berger, H.; Stewart, G. R.; Hennig, R. G.; Hirschfeld, P. J.; Hamlin, J. J.

    2017-03-01

    At ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to  ∼40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with T c values as high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute T c and find that our data is consistent with phonon-mediated superconductivity.

  1. Band Structure and Fermi Surface of Cu2Sb by the LMTO Method

    DEFF Research Database (Denmark)

    Jan, J. P.; Skriver, Hans Lomholt

    1977-01-01

    in four bands. The first and second bands contain closed sheets, degenerate along a plane in the absence of spin-orbit splitting. The third band contains a multiply-connected sheet. The fourth band consists of undulating columns, degenerate along a plane with the third band in the absence of spin...

  2. Mangrove vegetation structure in Southeast Brazil from phased array L-band synthetic aperture radar data

    Science.gov (United States)

    de Souza Pereira, Francisca Rocha; Kampel, Milton; Cunha-Lignon, Marilia

    2016-07-01

    The potential use of phased array type L-band synthetic aperture radar (PALSAR) data for discriminating distinct physiographic mangrove types with different forest structure developments in a subtropical mangrove forest located in Cananéia on the Southern coast of São Paulo, Brazil, is investigated. The basin and fringe physiographic types and the structural development of mangrove vegetation were identified with the application of the Kruskal-Wallis statistical test to the SAR backscatter values of 10 incoherent attributes. The best results to separate basin to fringe types were obtained using copolarized HH, cross-polarized HV, and the biomass index (BMI). Mangrove structural parameters were also estimated using multiple linear regressions. BMI and canopy structure index were used as explanatory variables for canopy height, mean height, and mean diameter at breast height regression models, with significant R2=0.69, 0.73, and 0.67, respectively. The current study indicates that SAR L-band images can be used as a tool to discriminate physiographic types and to characterize mangrove forests. The results are relevant considering the crescent availability of freely distributed SAR images that can be more utilized for analysis, monitoring, and conservation of the mangrove ecosystem.

  3. Contrasting 1D tunnel-structured and 2D layered polymorphs of V2O5: relating crystal structure and bonding to band gaps and electronic structure.

    Science.gov (United States)

    Tolhurst, Thomas M; Leedahl, Brett; Andrews, Justin L; Marley, Peter M; Banerjee, Sarbajit; Moewes, Alexander

    2016-06-21

    New V2O5 polymorphs have risen to prominence as a result of their open framework structures, cation intercalation properties, tunable electronic structures, and wide range of applications. The application of these materials and the design of new, useful polymorphs requires understanding their defining structure-property relationships. We present a characterization of the band gap and electronic structure of nanowires of the novel ζ-phase and the orthorhombic α-phase of V2O5 using X-ray spectroscopy and density functional theory calculations. The band gap is found to decrease from 1.90 ± 0.20 eV in the α-phase to 1.50 ± 0.20 eV in the ζ-phase, accompanied by the loss of the α-phase's characteristic split-off dxy band in the ζ-phase. States of dxy origin continue to dominate the conduction band edge in the new polymorph but the inequivalence of the vanadium atoms and the increased local symmetry of [VO6] octahedra results in these states overlapping with the rest of the V 3d conduction band. ζ-V2O5 exhibits anisotropic conductivity along the b direction, defining a 1D tunnel, in contrast to α-V2O5 where the anisotropic conductivity is along the ab layers. We explain the structural origins of the differences in electronic properties that exist between the α- and ζ-phase.

  4. Superconductivity in a chiral nanotube

    Science.gov (United States)

    Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.

    2017-02-01

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity--unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

  5. $^{16}$O + $^{16}$O molecular structures of positive- and negative-parity superdeformed bands in $^{34}$S

    CERN Document Server

    Taniguchi, Yasutaka

    2014-01-01

    The structures of excited states in $^{34}$S are investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter $\\beta$. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity superdeformed (SD) bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of $^{16}$O + $^{16}$O + two valence neutrons in molecular orbitals around the two $^{16}$O cores in a cluster picture. The configurations of the two valence neutrons are $\\delta^2$ and $\\pi^2$ for the positive-parity SD bands and $\\pi^1\\delta^1$ for the negative-parity SD band. The structural changes of the yrast states are also discussed.

  6. A Reconfigurable Triple-Notch-Band Antenna Integrated with Defected Microstrip Structure Band-Stop Filter for Ultra-Wideband Cognitive Radio Applications

    Directory of Open Access Journals (Sweden)

    Yingsong Li

    2013-01-01

    Full Text Available A printed reconfigurable ultra-wideband (UWB monopole antenna with triple narrow band-notched characteristics is proposed for cognitive radio applications in this paper. The triple narrow band-notched frequencies are obtained using a defected microstrip structure (DMS band stop filter (BSF embedded in the microstrip feed line and an inverted π-shaped slot etched in the rectangular radiation patch, respectively. Reconfigurable characteristics of the proposed cognitive radio antenna (CRA are achieved by means of four ideal switches integrated on the DMS-BSF and the inverted π-shaped slot. The proposed UWB CRA can work at eight modes by controlling switches ON and OFF. Moreover, impedance bandwidth, design procedures, and radiation patterns are presented for analysis and explanation of this antenna. The designed antenna operates over the frequency band between 3.1 GHz and 14 GHz (bandwidth of 127.5%, with three notched bands from 4.2 GHz to 6.2 GHz (38.5%, 6.6 GHz to 7.0 GHz (6%, and 12.2 GHz to 14 GHz (13.7%. The antenna is successfully simulated, fabricated, and measured. The results show that it has wide impedance bandwidth, multimodes characteristics, stable gain, and omnidirectional radiation patterns.

  7. Direct evidence for two-band superconductivity in MgB2 single crystals from directional point-contact spectroscopy in magnetic fields.

    Science.gov (United States)

    Gonnelli, R S; Daghero, D; Ummarino, G A; Stepanov, V A; Jun, J; Kazakov, S M; Karpinski, J

    2002-12-01

    We present the results of the first directional point-contact spectroscopy experiments in high-quality MgB2 single crystals. Because of the directionality of the current injection into the samples, the application of a magnetic field allowed us to separate the contributions of the sigma and pi bands to the total conductance of our point contacts. By using this technique, we were able to obtain the temperature dependency of each gap independent of the other. The consequent, strong reduction of the error on the value of the gap amplitude as a function of temperature allows a stricter test of the predictions of the two-band model for MgB2.

  8. 8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

    Energy Technology Data Exchange (ETDEWEB)

    Gladysiewicz, M.; Wartak, M. S. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5 (Canada); Kudrawiec, R. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

    2015-08-07

    The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ≤ 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 × 10{sup 18 }cm{sup −3}, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (ε = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 μm. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 μm and 1.55 μm) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga{sub 0.47}In{sub 0.53}As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 μm, i.e., at the wavelengths that are not available in current InP-based lasers.

  9. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films.

    Science.gov (United States)

    Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

    2016-02-08

    The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

  10. Quasiclassical description of multi-band superconductors with two order parameters

    Energy Technology Data Exchange (ETDEWEB)

    Moor, Andreas

    2014-05-19

    This Thesis deals with multi-band superconductors with two order parameters, i.e., the superconductivity and the spin-density wave, also touching on one-band superconductors with a charge-density wave, as well as with only the superconducting order parameter. Quasiclassical description of suchlike structures is developed and applied to investigation of various effects, inter alia, the Josephson and the proximity effects, the Knight shift, the Larkin-Ovchinnikov-Fulde-Ferrell-like state, and the interplay of the order parameters in coexistence regime. The applicability of the developed approach to pnictides is discussed.

  11. Microscopic annealing process and its impact on superconductivity in T'-structure electron-doped copper oxides.

    Science.gov (United States)

    Kang, Hye Jung; Dai, Pengcheng; Campbell, Branton J; Chupas, Peter J; Rosenkranz, Stephan; Lee, Peter L; Huang, Qingzhen; Li, Shiliang; Komiya, Seiki; Ando, Yoichi

    2007-03-01

    High-transition-temperature superconductivity arises in copper oxides when holes or electrons are doped into the CuO(2) planes of their insulating parent compounds. Whereas hole doping quickly induces metallic behaviour and superconductivity in many cuprates, electron doping alone is insufficient in materials such as R(2)CuO(4) (R is Nd, Pr, La, Ce and so on), where it is necessary to anneal an as-grown sample in a low-oxygen environment to remove a tiny amount of oxygen in order to induce superconductivity. Here we show that the microscopic process of oxygen reduction repairs Cu deficiencies in the as-grown materials and creates oxygen vacancies in the stoichiometric CuO(2) planes, effectively reducing disorder and providing itinerant carriers for superconductivity. The resolution of this long-standing materials issue suggests that the fundamental mechanism for superconductivity is the same for electron- and hole-doped copper oxides.

  12. Structural analysis and manufacture for the vacuum vessel of experimental advanced superconducting tokamak (EAST) device

    Energy Technology Data Exchange (ETDEWEB)

    Song Yuntao [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Anhui, Hefei 230031 (China)]. E-mail: songyt@ipp.ac.cn; Yao Damao [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Anhui, Hefei 230031 (China); Wu Songata [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Anhui, Hefei 230031 (China); Weng Peide [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Anhui, Hefei 230031 (China)

    2006-02-15

    The experimental advanced superconducting tokamak (EAST) is an advanced steady-state plasma physics experimental device, which has been approved by the Chinese government and is being constructed as the Chinese national nuclear fusion research project. The vacuum vessel, that is one of the key components, will have to withstand not only the electromagnetic force due to the plasma disruption and the Halo current, but also the pressure of boride water and the thermal stress due to the 250 deg. C baking out by the hot pressure nitrogen gas, or the 100 deg. C hot wall during plasma operation. This paper is a report of the mechanical analyses of the vacuum vessel. According to the allowable stress criteria of American Society of Mechanical Engineers, Boiler and Pressure Vessel Committee (ASME), the maximum integrated stress intensity on the vacuum vessel is 396 MPa, less than the allowable design stress intensity 3S {sub m} (441 MPa). At the same time, some key R and D issues are presented, which include supporting system, bellows and the assembly of the whole vacuum vessel.

  13. Classification of magnetic inhomogeneities and 0 -π transitions in superconducting-magnetic hybrid structures

    Science.gov (United States)

    Baker, Thomas E.; Richie-Halford, Adam; Bill, Andreas

    2016-09-01

    We present a comparative study of pair correlations and currents through superconducting-magnetic hybrid systems with a particular emphasis on the tunable Bloch domain wall of an exchange spring. This study of the Gor'kov functions contrasts magnetic systems with domain walls that change at discrete points in the magnetic region with those that change continuously throughout. We present results for misaligned homogeneous magnetic multilayers, including spin valves, for discrete domain walls, as well as exchange springs and helical domain walls—such as Holmium—for the continuous case. Introducing a rotating basis to disentangle the role of singlet and triplet correlations, we demonstrate that substantial amounts of (so-called short-range) singlet correlations are generated throughout the magnetic system in a continuous domain wall via the cascade effect. We propose a classification of 0 -π transitions of the Josephson current into three types, according to the predominant pair correlations symmetries involved in the current. Properties of exchange springs for an experimental study of the proposed effects are discussed. The interplay between components of the Gor'kov function that are parallel and perpendicular to the local magnetization lead to a novel prediction about their role in a proximity system with a progressively twisting helix that is experimentally measurable.

  14. First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2

    Institute of Scientific and Technical Information of China (English)

    HOU Xing-Gang; LIU An-Dong; HUANG Mei-Dong; LIAO Bin; WU Xiao-Ling

    2009-01-01

    The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density funetionai theory with the full-potentiai linearized-augraented-plane-wave method.New occupied bands ore found between the band gaps of both Ag-doped rutile and anatase TiO2.The formation of these new bands Capri be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption.

  15. On the Design of Laser Structured Ka Band Multi-Chip Module

    Directory of Open Access Journals (Sweden)

    Ghulam Mehdi

    2013-09-01

    Full Text Available The rapid prototyping of millimeter wave (MMW multi-chip module (MCM on low-cost ceramic-polymer composite substrate using laser ablation process is presented. A Ka band MCM front-end receiver is designed, fabricated and tested. The complete front-end receiver module except the IF and power distribution sections is realized on the single prescribed substrate. The measured receiver gain, noise figure and image rejection is 37 dB, 4.25 dB and 40 dB respectively. However, it deduced from the experimental results of the two front-end modules that the complex permittivity characteristics of the substrate are altered after the laser ablation process. The effective permittivity alteration phenomenon is further validated through the characterization and comparison of various laser ablated and chemically etched Ka band parallel-coupled band-pass filters. A simple and experimentally verified method is worked out to utilize the laser ablation structuring process on the prescribed substrate. It is anticipated that the proposed method can be applied to other laminated substrates as well with the prescribed manufacturing process.

  16. Core levels, valence band structure and unoccupied states of clean InN surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Himmerlich, Marcel; Eisenhardt, Anja; Schaefer, Juergen A.; Krischok, Stefan [Institut fuer Physik and Institut fuer Mikro- und Nanotechnologien, TU Ilmenau (Germany)

    2008-07-01

    In this study we used a surface analytics system directly connected to a MBE growth module to study the surface properties of thin InN films. The samples were prepared by plasma assisted molecular beam epitaxy on GaN/Al{sub 2}O{sub 3}(0001) templates and exhibited a 2 x 2 reconstruction after growth. The prepared samples were analysed by photoelectron spectroscopy as well as electron energy loss spectroscopy (EELS). For the occupied states, a very good agreement to available theoretical calculations is found. Although, the valence band maximum is located at 1.6 eV, indicating strong downward band bending of {proportional_to}0.9 eV, photoemission is detected up to E{sub F}. This indicates that the Fermi level is pinned above the conduction band minimum, as recently predicted. The spin-orbit splitting of the In 4d level at 17.8 eV could be resolved using He II radiation. Furthermore, from the fine structure of the secondary electron cascade peak we extract the energy of different unoccupied states 0 eV to 9 eV above the vacuum level. These measurements enable us to identify features in the InN EELS spectra, with a loss energy larger than 16 eV, as interband transitions from the In 4d level.

  17. Design and Characterization of a W-Band Folded-Waveguide Slow-Wave Structure

    Science.gov (United States)

    Sumathy, Murugan; Datta, Subrata Kumar

    2016-12-01

    A single-section slow-wave structure for a W-band folded-waveguide traveling-wave tube with operating bandwidth of around 4% was designed for delivering the output power of 50 W at the operating voltage of 13.5 kV and operating beam current of 80 mA. The design was carried out using analytical formulations and 3D electromagnetic simulations. The beam-wave interaction analysis was carried out using large signal Lagrangian analysis and particle-in-cell simulation. The folded-waveguide slow-wave structure along with input-output couplers and RF windows were fabricated. Cold test measurements were carried out for dispersion characteristics of the slow-wave structure and voltage standing-wave ratio and insertion loss characteristics of the RF window. The measured cold circuit parameters show close agreement with the analysis.

  18. Manipulation of Optoelectronic Properties and Band Structure Engineering of Ultrathin Te Nanowires by Chemical Adsorption.

    Science.gov (United States)

    Roy, Ahin; Amin, Kazi Rafsanjani; Tripathi, Shalini; Biswas, Sangram; Singh, Abhishek K; Bid, Aveek; Ravishankar, N

    2017-01-13

    Band structure engineering is a powerful technique both for the design of new semiconductor materials and for imparting new functionalities to existing ones. In this article, we present a novel and versatile technique to achieve this by surface adsorption on low dimensional systems. As a specific example, we demonstrate, through detailed experiments and ab initio simulations, the controlled modification of band structure in ultrathin Te nanowires due to NO2 adsorption. Measurements of the temperature dependence of resistivity of single ultrathin Te nanowire field-effect transistor (FET) devices exposed to increasing amounts of NO2 reveal a gradual transition from a semiconducting to a metallic state. Gradual quenching of vibrational Raman modes of Te with increasing concentration of NO2 supports the appearance of a metallic state in NO2 adsorbed Te. Ab initio simulations attribute these observations to the appearance of midgap states in NO2 adsorbed Te nanowires. Our results provide fundamental insights into the effects of ambient on the electronic structures of low-dimensional materials and can be exploited for designing novel chemical sensors.

  19. Estimating tropical forest structure using LIDAR AND X-BAND INSAR

    Science.gov (United States)

    Palace, M. W.; Treuhaft, R. N.; Keller, M. M.; Sullivan, F.; Roberto dos Santos, J.; Goncalves, F. G.; Shimbo, J.; Neumann, M.; Madsen, S. N.; Hensley, S.

    2013-12-01

    Tropical forests are considered the most structurally complex of all forests and are experiencing rapid change due to anthropogenic and climatic factors. The high carbon stocks and fluxes make understanding tropical forests highly important to both regional and global studies involving ecosystems and climate. Large and remote areas in the tropics are prime targets for the use of remotely sensed data. Radar and lidar have previously been used to estimate forest structure, with an emphasis on biomass. These two remote sensing methods have the potential to yield much more information about forest structure, specifically through the use of X-band radar and waveform lidar data. We examined forest structure using both field-based and remotely sensed data in the Tapajos National Forest, Para, Brazil. We measured multiple structural parameters for about 70 plots in the field within a 25 x 15 km area that have TanDEM-X single-pass horizontally and vertically polarized radar interferometric data. High resolution airborne lidar were collected over a 22 sq km portion of the same area, within which 33 plots were co-located. Preliminary analyses suggest that X-band interferometric coherence decreases by about a factor of 2 (from 0.95 to 0.45) with increasing field-measured vertical extent (average heights of 7-25 m) and biomass (10-430 Mg/ha) for a vertical wavelength of 39 m, further suggesting, as has been observed at C-band, that interferometric synthetic aperture radar (InSAR) is substantially more sensitive to forest structure/biomass than SAR. Unlike InSAR coherence versus biomass, SAR power at X-band versus biomass shows no trend. Moreover, airborne lidar coherence at the same vertical wavenumbers as InSAR is also shown to decrease as a function of biomass, as well. Although the lidar coherence decrease is about 15% more than the InSAR, implying that lidar penetrates more than InSAR, these preliminary results suggest that X-band InSAR may be useful for structure and

  20. Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Hunte, F. [Florida State University; Jaroszynski, J. [Florida State University; Gurevich, A. [Florida State University; Larbalestier, D. C. [Florida State University; Jin, Rongying [ORNL; Safa-Sefat, Athena [ORNL; McGuire, Michael A [ORNL; Sales, Brian C [ORNL; Christen, David K [ORNL; Mandrus, David [ORNL

    2008-01-01

    The recent synthesis of the superconductor LaFeAsO{sub 0.89}F{sub 0.11} with transition temperature T{sub c} {approx} 26 K (refs 1-4) has been quickly followed by reports of even higher transition temperatures in related compounds: 41 K in CeFeAsO{sub 0.84}F{sub 0.16} (ref. 5), 43 K in SmFeAsO{sub 0.9}F{sub 0.1} (ref. 6), and 52 K in NdFeAsO{sub 0.89}F{sub 0.11} and PrFeAsO{sub 0.89}F{sub 0.11}. These discoveries have generated much interest in the mechanisms and manifestations of unconventional superconductivity in the family of doped quaternary layered oxypnictides LnOTMPn (Ln: La, Pr, Ce, Sm; TM: Mn, Fe, Co, Ni; Pn: P, As), because many features of these materials set them apart from other known superconductors. Here we report resistance measurements of LaFeAsO{sub 0.89}F{sub 0.11} at high magnetic fields, up to 45 T, that show a remarkable enhancement of the upper critical field B{sub c2} compared to values expected from the slopes dB{sub c2}/dT 2 T K{sup -1} near T{sub c}, particularly at low temperatures where the deduced B{sub c2}(0) 63-65 T exceeds the paramagnetic limit. We argue that oxypnictides represent a new class of high-field superconductors with B{sub c2} values surpassing those of Nb{sub 3}Sn, MgB{sub 2} and the Chevrel phases, and perhaps exceeding the 100 T magnetic field benchmark of the high-T{sub c} copper oxides.

  1. Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields.

    Science.gov (United States)

    Hunte, F; Jaroszynski, J; Gurevich, A; Larbalestier, D C; Jin, R; Sefat, A S; McGuire, M A; Sales, B C; Christen, D K; Mandrus, D

    2008-06-12

    The recent synthesis of the superconductor LaFeAsO(0.89)F(0.11) with transition temperature T(c) approximately 26 K (refs 1-4) has been quickly followed by reports of even higher transition temperatures in related compounds: 41 K in CeFeAsO(0.84)F(0.16) (ref. 5), 43 K in SmFeAsO(0.9)F(0.1) (ref. 6), and 52 K in NdFeAsO(0.89)F(0.11) and PrFeAsO(0.89)F(0.11) (refs 7, 8). These discoveries have generated much interest in the mechanisms and manifestations of unconventional superconductivity in the family of doped quaternary layered oxypnictides LnOTMPn (Ln: La, Pr, Ce, Sm; TM: Mn, Fe, Co, Ni; Pn: P, As), because many features of these materials set them apart from other known superconductors. Here we report resistance measurements of LaFeAsO(0.89)F(0.11) at high magnetic fields, up to 45 T, that show a remarkable enhancement of the upper critical field B(c2) compared to values expected from the slopes dB(c2)/dT approximately 2 T K(-1) near T(c), particularly at low temperatures where the deduced B(c2)(0) approximately 63-65 T exceeds the paramagnetic limit. We argue that oxypnictides represent a new class of high-field superconductors with B(c2) values surpassing those of Nb(3)Sn, MgB(2) and the Chevrel phases, and perhaps exceeding the 100 T magnetic field benchmark of the high-T(c) copper oxides.

  2. Band structure and transport studies of copper selenide: An efficient thermoelectric material

    Science.gov (United States)

    Tyagi, Kriti; Gahtori, Bhasker; Bathula, Sivaiah; Auluck, S.; Dhar, Ajay

    2014-10-01

    We report the band structure calculations for high temperature cubic phase of copper selenide (Cu2Se) employing Hartree-Fock approximation using density functional theory within the generalized gradient approximation. These calculations were further extended to theoretically estimate the electrical transport coefficients of Cu2Se employing Boltzmann transport theory, which show a reasonable agreement with the corresponding experimentally measured values. The calculated transport coefficients are discussed in terms of the thermoelectric (TE) performance of this material, which suggests that Cu2Se can be a potential p-type TE material with an optimum TE performance at a carrier concentration of ˜ 4 - 6 × 10 21 cm - 3 .

  3. Staggering of the B(M1) value as a fingerprint of specific chiral bands structure

    CERN Document Server

    Grodner, Ernest

    2011-01-01

    Nuclear chirality has been intensively studdied for the last several years in the context of experimental as well as theoretical approach. Characteristic gamma selection rules have been predicted for the strong chiral symmetry breaking limit that has been observed in Cs isotopes. The presented analysis shows that the gamma selection rules cannot be attributed only to chiral symmetry breaking. The selection rules relate to structural composition of the chiral rotational bands, i.e. to odd particle configuration and the deformation of the core.

  4. Exceptional contours and band structure design in parity-time symmetric photonic crystals

    CERN Document Server

    Cerjan, Alexander; Fan, Shanhui

    2016-01-01

    We investigate the properties of multidimensional parity-time symmetric periodic systems whose non-Hermitian periodicity is an integer multiple of the underlying Hermitian system's periodicity. This creates a natural set of degeneracies which can undergo thresholdless $\\mathcal{PT}$ transitions. We derive a $\\mathbf{k} \\cdot \\mathbf{p}$ perturbation theory suited to the continuous eigenvalues of such systems in terms of the modes of the underlying Hermitian system. In photonic crystals, such thresholdless $\\mathcal{PT}$ transitions are shown to yield significant control over the band structure of the system, and can result in all-angle supercollimation, a $\\mathcal{PT}$-superprism effect, and unidirectional behavior.

  5. Energy-band structure and intrinsic coherent properties in two weakly linked Bose-Einstein condensates

    Science.gov (United States)

    Li, Wei-Dong; Zhang, Yunbo; Liang, J.-Q.

    2003-06-01

    The energy-band structure and energy splitting due to quantum tunneling in two weakly linked Bose-Einstein condensates were calculated by using the instanton method. The intrinsic coherent properties of Bose-Josephson junction (BJJ) were investigated in terms of energy splitting. For EC/EJ≪1, the energy splitting is small and the system is globally phase coherent. In the opposite limit, EC/EJ≫1, the energy splitting is large and the system becomes phase dissipated. Our results suggest that one should investigate the coherence phenomena of BJJ in proper condition such as EC/EJ˜1.

  6. Photonic Band Gaps in 3D Network Structures with Short-range Order

    CERN Document Server

    Liew, Seng Fatt; Noh, Heeso; Schreck, Carl F; Dufresne, Eric R; O'Hern, Corey S; Cao, Hui

    2011-01-01

    We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PAS) with short-range order. From calculations of the density of optical states (DOS) for PAS with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PAS, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PAS without long-range order.

  7. Competition between magnetic field dependent band structure and coherent backscattering in multiwall carbon nanotubes

    Science.gov (United States)

    Stojetz, B.; Roche, S.; Miko, C.; Triozon, F.; Forró, L.; Strunk, C.

    2007-03-01

    Magnetotransport measurements in large diameter multiwall carbon nanotubes (20 40 nm) demonstrate the competition of a magnetic-field dependent bandstructure and Altshuler Aronov Spivak oscillations. By means of an efficient capacitive coupling to a backgate electrode, the magnetoconductance oscillations are explored as a function of Fermi level shift. Changing the magnetic field orientation with respect to the tube axis and by ensemble averaging, allows the contributions of different Aharonov Bohm phases to be identified. The results are in qualitative agreement with numerical calculations of the band structure and the conductance.

  8. First principles electronic band structure and phonon dispersion curves for zinc blend beryllium chalcogenide

    Energy Technology Data Exchange (ETDEWEB)

    Dabhi, Shweta, E-mail: venu.mankad@gmail.com; Mankad, Venu, E-mail: venu.mankad@gmail.com; Jha, Prafulla K., E-mail: venu.mankad@gmail.com [Department of Physics, Maharaja Krishnakumasinhji Bhavnagar University, Bhavnagar-364001 (India)

    2014-04-24

    A detailed theoretical study of structural, electronic and Vibrational properties of BeX compound is presented by performing ab-initio calculations based on density-functional theory using the Espresso package. The calculated value of lattice constant and bulk modulus are compared with the available experimental and other theoretical data and agree reasonably well. BeX (X = S,Se,Te) compounds in the ZB phase are indirect wide band gap semiconductors with an ionic contribution. The phonon dispersion curves are represented which shows that these compounds are dynamically stable in ZB phase.

  9. Exceptional Contours and Band Structure Design in Parity-Time Symmetric Photonic Crystals.

    Science.gov (United States)

    Cerjan, Alexander; Raman, Aaswath; Fan, Shanhui

    2016-05-20

    We investigate the properties of two-dimensional parity-time symmetric periodic systems whose non-Hermitian periodicity is an integer multiple of the underlying Hermitian system's periodicity. This creates a natural set of degeneracies that can undergo thresholdless PT transitions. We derive a k·p perturbation theory suited to the continuous eigenvalues of such systems in terms of the modes of the underlying Hermitian system. In photonic crystals, such thresholdless PT transitions are shown to yield significant control over the band structure of the system, and can result in all-angle supercollimation, a PT-superprism effect, and unidirectional behavior.

  10. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, Kevin Jerome [Iowa State Univ., Ames, IA (United States)

    2001-06-27

    Over the last ten years, photonic band gap (PBG) theory and technology have become an important area of research because of the numerous possible applications ranging from high-efficiency laser diodes to optical circuitry. This research concentrates on reducing the length scale in the fabrication of layered photonic band gap structures and developing procedures to improve processing consistency. Various procedures and materials have been used in the fabrication of layered PBG structures. This research focused on an economical micro transfer molding approach to create the final PBG structure. A poly dimethylsiloxane (PDMS) rubber mold was created from a silicon substrate. It was filled with epoxy and built layer-by-layer to create a 3-D epoxy structure. This structure was infiltrated with nanoparticle titania or a titania sol-gel, then fired to remove the polymer mold, leaving a monolithic ceramic inverse of the epoxy structure. The final result was a lattice of titania rolds that resembles a face-centered tetragonal structure. The original intent of this research was to miniaturize this process to a bar size small enough to create a photonic band gap for wavelengths of visible electro-magnetic radiation. The factor limiting progress was the absence of a silicon master mold of small enough dimensions. The Iowa State Microelectronics Research Center fabricated samples with periodicities of 2.5 and 1.0 microns with the existing technology, but a sample was needed on the order of 0.3 microns or less. A 0.4 micron sample was received from Sandia National Laboratory, which was made through an electron beam lithography process, but it contained several defects. The results of the work are primarily from the 2.5 and 1.0 micron samples. Most of the work focused on changing processing variables in order to optimize the infiltration procedure for the best results. Several critical parameters were identified, ranging from the ambient conditions to the specifics of the

  11. Local structure, stripe pinning, and superconductivity in La1.875Ba0.125CuO4 at high pressure

    Science.gov (United States)

    Fabbris, G.; Hücker, M.; Gu, G. D.; Tranquada, J. M.; Haskel, D.

    2013-08-01

    The interplay between stripe correlations, local structure, and superconductivity in La1.875Ba0.125CuO4 is studied with concomitant polarized x-ray absorption fine structure (XAFS) and x-ray diffraction measurements at high pressure. Long-range order of the CuO6 octahedral tilt pattern that pins charge-stripe order vanishes at a pressure-induced structural transition (P=1.8 GPa at T=5 K). Diffraction shows that static charge stripe and associated octahedral tilt correlations which survive in the high-pressure phase are effectively suppressed above 3.5 GPa. In contrast, XAFS analysis shows that instantaneous local correlations of the characteristic octahedral tilt pattern remain robust to at least 5 GPa. The decreasing local tilt angle is well correlated with a gradual increase in the superconducting transition temperature, suggesting that orientational pinning of charge correlations can survive the loss of static stripe order.

  12. Probing the connections between superconductivity, stripe order, and structure in La1.905Ba0.095Cu1-yZnyO4

    Science.gov (United States)

    Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Jie, Qing; Hücker, M.; Zheludev, A.; Tian, Wei; Winn, B. L.; Zarestky, J. L.; Singh, D. K.; Hong, Tao; Li, Qiang; Gu, Genda; Tranquada, J. M.

    2012-04-01

    The superconducting system La2-xBaxCuO4 is known to show a minimum in the transition temperature Tc at x=(1)/(8) where maximal stripe order is pinned by the anisotropy within the CuO2 planes that occurs in the low-temperature-tetragonal (LTT) crystal structure. For x=0.095, where Tc reaches its maximum value of 32 K, there is a roughly coincident structural transition to a phase that is very close to LTT. Here, we present a neutron scattering study of the structural transition, and demonstrate how features of it correlate with anomalies in the magnetic susceptibility, electrical resistivity, thermal conductivity, and thermoelectric power. We also present measurements on a crystal with 1% Zn substituted for Cu, which reduces Tc to 17 K, enhances the spin stripe order, but has much less effect on the structural transition. We make the case that the structural transition correlates with a reduction of the Josephson coupling between the CuO2 layers, which interrupts the growth of the superconducting order. We also discuss evidence for two-dimensional superconducting fluctuations in the normal state, analyze the effective magnetic moment per Zn impurity, and consider the significance of the anomalous thermopower often reported in the stripe-ordered phase.

  13. Probing the connections between superconductivity, stripe order, and structure in La1.905Ba0.095Cu1 yZnyO4

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Jinsheng [University of California, Berkeley; Xu, Zhijun [Brookhaven National Laboratory (BNL); Xu, Guangyong [Brookhaven National Laboratory (BNL); Jie, Qing [Brookhaven National Laboratory (BNL); Hucker, M. [Brookhaven National Laboratory (BNL); Zheludev, A [ETH Zurich, Switzerland; Tian, Wei [Ames Laboratory and Iowa State University; Winn, Barry L [ORNL; Zarestky, Jerel L [ORNL; Singh, D. K. [University of Maryland and NIST; Hong, Tao [ORNL; Li, Qiang [Brookhaven National Laboratory (BNL); Gu, Genda [Brookhaven National Laboratory (BNL); Tranquada, John M. [Brookhaven National Laboratory (BNL)

    2012-01-01

    The superconducting system La2 xBaxCuO4 is known to show a minimum in the transition temperature, Tc, at x = 1/8 where maximal stripe order is pinned by the anisotropy within the CuO2 planes that occurs in the low-temperature-tetragonal (LTT) crystal structure. For x = 0.095, where Tc reaches its maximum value of 32 K, there is a roughly coincident structural transition to a phase that is very close to LTT. Here we present a neutron scattering study of the structural transition, and demonstrate how features of it correlate with anomalies in the magnetic susceptibility, electrical resistivity, thermal conductivity, and thermoelectric power. We also present measurements on a crystal with 1% Zn substituted for Cu, which reduces Tc to 17 K, enhances the spin stripe order, but has much less effect on the structural transition. We make the case that the structural transition correlates with a reduction of the Josephson coupling between the CuO2 layers, which interrupts the growth of the superconducting order. We also discuss evidence for two-dimensional superconducting fluctuations in the normal state, analyze the effective magnetic moment per Zn impurity, and consider the significance of the anomalous thermopower often reported in the stripeordered phase.

  14. Correlated Band Structure of a Transition Metal Oxide ZnO Obtained from a Many-Body Wave Function Theory

    Science.gov (United States)

    Ochi, Masayuki; Arita, Ryotaro; Tsuneyuki, Shinji

    2017-01-01

    Obtaining accurate band structures of correlated solids has been one of the most important and challenging problems in first-principles electronic structure calculation. There have been promising recent active developments of wave function theory for condensed matter, but its application to band-structure calculation remains computationally expensive. In this Letter, we report the first application of the biorthogonal transcorrelated (BITC) method: self-consistent, free from adjustable parameters, and systematically improvable many-body wave function theory, to solid-state calculations with d electrons: wurtzite ZnO. We find that the BITC band structure better reproduces the experimental values of the gaps between the bands with different characters than several other conventional methods. This study paves the way for reliable first-principles calculations of the properties of strongly correlated materials.

  15. 16O + 16O molecular structures of positive- and negative-parity superdeformed bands in 34S

    Directory of Open Access Journals (Sweden)

    Taniguchi Yasutaka

    2016-01-01

    Full Text Available The structures of excited states in 34S are investigated using the antisymmetrized molecular dynamics and generator coordinate method(GCM. The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter β. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity super de formed(SD bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16O + 16O + two valence neutrons in molecular orbitals around the two 16O cores in a cluster picture. The configurations of the two valence neutrons are δ2 and π2 for the positive-parity SD bands and π1δ1 for the negative parity SD band.

  16. Correlation of Photocatalytic Activity with Band Structure of Low-dimensional Semiconductor Nanostructures

    Science.gov (United States)

    Meng, Fanke

    Photocatalytic hydrogen generation by water splitting is a promising technique to produce clean and renewable solar fuel. The development of effective semiconductor photocatalysts to obtain efficient photocatalytic activity is the key objective. However, two critical reasons prevent wide applications of semiconductor photocatalysts: low light usage efficiency and high rates of charge recombination. In this dissertation, several low-dimensional semiconductors were synthesized with hydrothermal, hydrolysis, and chemical impregnation methods. The band structures of the low-dimensional semiconductor materials were engineered to overcome the above mentioned two shortcomings. In addition, the correlation between the photocatalytic activity of the low-dimensional semiconductor materials and their band structures were studied. First, we studied the effect of oxygen vacancies on the photocatalytic activity of one-dimensional anatase TiO2 nanobelts. Given that the oxygen vacancy plays a significant role in band structure and photocatalytic performance of semiconductors, oxygen vacancies were introduced into the anatase TiO2 nanobelts during reduction in H2 at high temperature. The oxygen vacancies of the TiO2 nanobelts boosted visible-light-responsive photocatalytic activity but weakened ultraviolet-light-responsive photocatalytic activity. As oxygen vacancies are commonly introduced by dopants, these results give insight into why doping is not always beneficial to the overall photocatalytic performance despite increases in absorption. Second, we improved the photocatalytic performance of two-dimensional lanthanum titanate (La2Ti2 O7) nanosheets, which are widely studied as an efficient photocatalyst due to the unique layered crystal structure. Nitrogen was doped into the La2Ti2O7 nanosheets and then Pt nanoparticles were loaded onto the La2Ti2O7 nanosheets. Doping nitrogen narrowed the band gap of the La2Ti 2O7 nanosheets by introducing a continuum of states by the valence

  17. Numerical and Experimental Investigation of Stop-Bands in Finite and Infinite Periodic One-Dimensional Structures

    DEFF Research Database (Denmark)

    Domadiya, Parthkumar Gandalal; Manconi, Elisabetta; Vanali, Marcello;

    2016-01-01

    method deals with the evaluation of a vibration level difference (VLD) in a finite periodic structure embedded within an infinite one-dimensional waveguide. This VLD is defined to predict the performance in terms of noise and vibration insulation of periodic cells embedded in an otherwise uniform...... vibration and noise transmission. The aim of this paper is to investigate, numerically and experimentally, stop-bands in periodic one-dimensional structures. Two methods for pre-dicting stop-bands are described: the first method applies to infinite periodic structures using a wave approach; the second...... of the structure) predict those obtained from the VLD of the corresponding finite periodic structure....

  18. Electronic materials high-T(sub c) superconductivity polymers and composites structural materials surface science and catalysts industry participation

    Science.gov (United States)

    1988-01-01

    The fifth year of the Center for Advanced Materials was marked primarily by the significant scientific accomplishments of the research programs. The Electronics Materials program continued its work on the growth and characterization of gallium arsenide crystals, and the development of theories to understand the nature and distribution of defects in the crystals. The High Tc Superconductivity Program continued to make significant contributions to the field in theoretical and experimental work on both bulk materials and thin films and devices. The Ceramic Processing group developed a new technique for cladding YBCO superconductors for high current applications in work with the Electric Power Research Institute. The Polymers and Composites program published a number of important studies involving atomistic simulations of polymer surfaces with excellent correlations to experimental results. The new Enzymatic Synthesis of Materials project produced its first fluorinated polymers and successfully began engineering enzymes designed for materials synthesis. The structural Materials Program continued work on novel alloys, development of processing methods for advanced ceramics, and characterization of mechanical properties of these materials, including the newly documented characterization of cyclic fatigue crack propagation behavior in toughened ceramics. Finally, the Surface Science and Catalysis program made significant contributions to the understanding of microporous catalysts and the nature of surface structures and interface compounds.

  19. Low-lying levels and high-spin band structures in sup 1 sup 0 sup 2 Rh

    CERN Document Server

    Gizon, J; Timar, J; Cata-Danil, G; Nyakó, B M; Zolnai, L; Boston, A J; Joss, D T; Paul, E S; Semple, A T; O'Brien, N J; Parry, C M; Bucurescu, D; Brant, S; Paar, V

    1999-01-01

    Levels in sup 1 sup 0 sup 2 Rh have been populated in the reaction sup 7 sup 0 Zn+ sup 3 sup 6 S at 130 MeV. The level structure of sup 1 sup 0 sup 2 Rh has been investigated using the EUROGAM II array. Low-lying states and four high-spin bands have been identified. The configurations of low-lying levels and two-quasiparticle bands are interpreted in the frame of the interacting boson-fermion-fermion model. The four observed band structures are also compared with cranked shell model calculations using a modified oscillator potential.

  20. Bohr Hamiltonian with different mass parameters applied to band structures of Eu isotopes built on Nilsson orbitals

    Indian Academy of Sciences (India)

    ERMAMATOV M J; YÉPEZ-MARTÍNEZ H; SRIVASTAVA P C

    2016-05-01

    The band structure of the proton-odd nuclei $^{153,155}$Eu, built on Nilsson orbitals, is investigated within the framework of a recently developed extended Bohr Hamiltonian model. The relative distance between spherical orbitals is taken into account by considering single-particle energies as a parameter which changes with increasing neutron number. Energy levels of each band and$B(E2)$ values inside the ground-state band are calculated and compared with the available experimental data. Thus, more comprehensive information on the structure of deformed nuclei can be obtained by studying the rotation–vibration spectra of odd nuclei built on Nilsson single-particle orbitals.