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Sample records for quasiparticle band structure

  1. Quasiparticle band structure

    Energy Technology Data Exchange (ETDEWEB)

    Manghi, F., E-mail: franca.manghi@unimore.it [Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, Via Campi 213/A, I-41125 Modena (Italy); CNR – Institute of NanoSciences – S3 (Italy); Boni, V. [Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, Via Campi 213/A, I-41125 Modena (Italy)

    2015-04-15

    Highlights: • We review many body techniques for quasiparticle calculations. • We focus on transition metals and transition metal oxides. • We discuss spin dependent energy renormalization and quasiparticle quenching. • We present a detailed comparison between two methods (DMFT and 3BS).

  2. Quasiparticle band structure

    International Nuclear Information System (INIS)

    Manghi, F.; Boni, V.

    2015-01-01

    Highlights: • We review many body techniques for quasiparticle calculations. • We focus on transition metals and transition metal oxides. • We discuss spin dependent energy renormalization and quasiparticle quenching. • We present a detailed comparison between two methods (DMFT and 3BS).

  3. 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

  4. Quasiparticle semiconductor band structures including spin-orbit interactions.

    Science.gov (United States)

    Malone, Brad D; Cohen, Marvin L

    2013-03-13

    We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors.

  5. Study of multi-quasiparticle band structures in 197Tl using α beam

    International Nuclear Information System (INIS)

    Mukherjee, G.; Nandi, S.; Pai, H.

    2016-01-01

    Study of the multi-quasiparticle (qp) states and the band structures built on them in the neutron deficient Tl nuclei in A ∼ 190 mass region provides useful information on particle-hole interaction in the heavy nuclei. In order to investigate the multi-qp band structures we have studied the excited states in 197 Tl by gamma ray spectroscopy

  6. Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions.

    Science.gov (United States)

    Dixit, H; Lamoen, D; Partoens, B

    2013-01-23

    CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass.

  7. The quasiparticle band structure of zincblende and rocksalt ZnO.

    Science.gov (United States)

    Dixit, H; Saniz, R; Lamoen, D; Partoens, B

    2010-03-31

    We present the quasiparticle band structure of ZnO in its zincblende (ZB) and rocksalt (RS) phases at the Γ point, calculated within the GW approximation. The effect of the p-d hybridization on the quasiparticle corrections to the band gap is discussed. We compare three systems, ZB-ZnO which shows strong p-d hybridization and has a direct band gap, RS-ZnO which is also hybridized but includes inversion symmetry and therefore has an indirect band gap, and ZB-ZnS which shows a weaker hybridization due to a change of the chemical species from oxygen to sulfur. The quasiparticle corrections are calculated with different numbers of valence electrons in the Zn pseudopotential. We find that the Zn(20+) pseudopotential is essential for the adequate treatment of the exchange interaction in the self-energy. The calculated GW band gaps are 2.47 eV and 4.27 eV respectively, for the ZB and RS phases. The ZB-ZnO band gap is underestimated compared to the experimental value of 3.27 by ∼ 0.8 eV. The RS-ZnO band gap compares well with the experimental value of 4.5 eV. The underestimation for ZB-ZnO is correlated with the strong p-d hybridization. The GW band gap for ZnS is 3.57 eV, compared to the experimental value of 3.8 eV.

  8. Magnetic oscillations and quasiparticle band structure in the mixed state of type-II superconductors

    International Nuclear Information System (INIS)

    Norman, M.R.; MacDonald, A.H.; Akera, H.

    1995-01-01

    We consider magnetic oscillations due to Landau quantization in the mixed state of type-II superconductors. Our work is based on a previously developed formalism which allows the mean-field gap equations of the Abrikosov state to be conveniently solved in a Landau-level representation. We find that the quasiparticle band structure changes qualitatively when the pairing self-energy becomes comparable to the Landau-level separation. For small pairing self-energies, Landau-level mixing due to the superconducting order is weak and magnetic oscillations survive in the superconducting state although they are damped. We find that the width of the quasiparticle Landau levels in this regime varies approximately as Δ 0 n μ -1/4 where Δ 0 is proportional to the magnitude of the order parameter and n μ is the Landau-level index at the Fermi energy. For larger pairing self-energies, the lowest energy quasiparticle bands occur in pairs which are nearly equally spaced from each other and evolve with weakening magnetic field toward the bound states of an isolated vortex core. These bands have a weak magnetic field dependence and magnetic oscillations vanish rapidly in this regime. We discuss recent observations of the de Haas--van Alphen effect in the mixed state of several type-II superconductors in light of our results

  9. Quasiparticle band structure for the Hubbard systems: Application to α-CeAl2

    International Nuclear Information System (INIS)

    Costa-Quintana, J.; Lopez-Aguilar, F.; Balle, S.; Salvador, R.

    1990-01-01

    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 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 α-CeAl 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

  10. Dispersion Corrected Structural Properties and Quasiparticle Band Gaps of Several Organic Energetic Solids.

    Science.gov (United States)

    Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

    2015-06-18

    We have performed ab initio calculations for a series of energetic solids to explore their structural and electronic properties. To evaluate the ground state volume of these molecular solids, different dispersion correction methods were accounted in DFT, namely the Tkatchenko-Scheffler method (with and without self-consistent screening), Grimme's methods (D2, D3(BJ)), and the vdW-DF method. Our results reveal that dispersion correction methods are essential in understanding these complex structures with van der Waals interactions and hydrogen bonding. The calculated ground state volumes and bulk moduli show that the performance of each method is not unique, and therefore a careful examination is mandatory for interpreting theoretical predictions. This work also emphasizes the importance of quasiparticle calculations in predicting the band gap, which is obtained here with the GW approximation. We find that the obtained band gaps are ranging from 4 to 7 eV for the different compounds, indicating their insulating nature. In addition, we show the essential role of quasiparticle band structure calculations to correlate the gap with the energetic properties.

  11. Momentum-Space Imaging of the Dirac Band Structure in Molecular Graphene via Quasiparticle Interference

    Science.gov (United States)

    Stephenson, Anna; Gomes, Kenjiro K.; Ko, Wonhee; Mar, Warren; Manoharan, Hari C.

    2014-03-01

    Molecular graphene is a nanoscale artificial lattice composed of carbon monoxide molecules arranged one by one, realizing a dream of exploring exotic quantum materials by design. This assembly is done by atomic manipulation with a scanning tunneling microscope (STM) on a Cu(111) surface. To directly probe the transformation of normal surface state electrons into massless Dirac fermions, we map the momentum space dispersion through the Fourier analysis of quasiparticle scattering maps acquired at different energies with the STM. The Fourier analysis not only bridges the real-space and momentum-space data but also reveals the chiral nature of those quasiparticles, through a set of selection rules of allowed scattering involving the pseudospin and valley degrees of freedom. The graphene-like band structure can be reshaped with simple alterations to the lattice, such as the addition of a strain. We analyze the effect on the momentum space band structure of multiple types of strain on our system. Supported by DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515.

  12. Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

    Science.gov (United States)

    Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye A.; Sun, Yi-Yang; Zhang, Shengbai; Zhang, Peihong

    2016-02-01

    The quasiparticle band gap is one of the most important materials properties for photovoltaic applications. Often the band gap of a photovoltaic material is determined (and can be controlled) by various factors, complicating predictive materials optimization. An in-depth understanding of how these factors affect the size of the gap will provide valuable guidance for new materials discovery. Here we report a comprehensive investigation on the band gap formation mechanism in organic-inorganic hybrid perovskites by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Major factors, namely, quasiparticle self-energy, spin-orbit coupling, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organic-inorganic hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap by introducing structural distortions and controlling the overall lattice constants. The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies.

  13. Determination of band structure parameters and the quasi-particle gap of CdSe quantum dots by cyclic voltammetry.

    Science.gov (United States)

    Inamdar, Shaukatali N; Ingole, Pravin P; Haram, Santosh K

    2008-12-01

    Band structure parameters such as the conduction band edge, the valence band edge and the quasi-particle gap of diffusing CdSe quantum dots (Q-dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q-dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi-empirical pseudopotential method (SEPM)-especially in the strong size-confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q-dots, the difference between the quasi-particle gap and the optical band gap gives the electron-hole Coulombic interaction energy (J(e1,h1)). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.

  14. Microscopic mechanism of identical multi-quasiparticle bands

    International Nuclear Information System (INIS)

    Lei Yian; Zhao Enguang; Zeng Jinyan

    1997-01-01

    Identical one-quasiparticle and two-quasiparticle bands in neighboring odd-and even-mass nuclei are recognized; The intrinsic structure of identical bands is demonstrated by using the particle-number-conserving (PNC) treatment. The occurrence of almost identical moments of inertia is the result of competition among the shell effect (including shape variation), pairing (anti-alignment) effect and blocking (anti-pairing) effect. The observed moments of inertia of identical multi-quasiparticle bands are reproduced quite well by the PNC calculation

  15. Quasiparticle self-consistent GW calculations for PbS, PbSe, and PbTe: Band structure and pressure coefficients

    DEFF Research Database (Denmark)

    Svane, Axel; Christensen, Niels Egede; Cardona,, M.

    2010-01-01

    The electronic band structures of PbS, PbSe, and PbTe in the rocksalt structure are calculated with the quasiparticle self-consistent GW (QSGW) approach with spin-orbit coupling included. The semiconducting gaps and their deformation potentials as well as the effective masses are obtained. The GW...

  16. Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc.

    Science.gov (United States)

    Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon

    2015-07-24

    Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between d(x(2)-y(2)) and d(3z(2)-r(2)) is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc.

  17. Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields

    International Nuclear Information System (INIS)

    Brandow, B.H.

    1985-01-01

    Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs

  18. Relativistic quasiparticle band structures of Mg2Si, Mg2Ge, and Mg2Sn: Consistent parameterization and prediction of Seebeck coefficients

    Science.gov (United States)

    Shi, Guangsha; Kioupakis, Emmanouil

    2018-02-01

    We apply density functional and many-body perturbation theory calculations to consistently determine and parameterize the relativistic quasiparticle band structures of Mg2Si, Mg2Ge, and Mg2Sn, and predict the Seebeck coefficient as a function of doping and temperature. The quasiparticle band gaps, including spin-orbit coupling effects, are determined to be 0.728 eV, 0.555 eV, and 0.142 eV for Mg2Si, Mg2Ge, and Mg2Sn, respectively. The inclusion of the semicore electrons of Mg, Ge, and Sn in the valence is found to be important for the accurate determination of the band gaps of Mg2Ge and Mg2Sn. We also developed a Luttinger-Kohn Hamiltonian and determined a set of band parameters to model the near-edge relativistic quasiparticle band structure consistently for all three compounds that can be applied for thermoelectric device simulations. Our calculated values for the Seebeck coefficient of all three compounds are in good agreement with the available experimental data for a broad range of temperatures and carrier concentrations. Our results indicate that quasiparticle corrections are necessary for the accurate determination of Seebeck coefficients at high temperatures at which bipolar transport becomes important.

  19. Identical high- K three-quasiparticle rotational bands

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, Harjeet; Singh, Pardeep [Guru Nanak Dev University, Department of Physics, Amritsar (India)

    2016-12-15

    A comprehensive study of high-K three-quasiparticle rotational bands in odd-A nuclei indicates the similarity in γ-ray energies and dynamic moment of inertia I{sup (2)}. The extent of the identicality between the rotational bands is evaluated by using the energy factor method. For nuclei pairs exhibiting identical bands, the average relative change in the dynamic moment of inertia I{sup (2)} is also determined. The identical behaviour shown by these bands is attributed to the interplay of nuclear structure parameters: deformation and the pairing correlations. Also, experimental trend of the I(ℎ) vs. ℎω (MeV) plot for these nuclei pairs is shown to be in agreement with Tilted-Axis Cranking (TAC) model calculations. (orig.)

  20. Three- and five-quasiparticle isomers, rotational bands and residual interactions in 175Hf

    International Nuclear Information System (INIS)

    Dracoulis, G.D.; Walker, P.M.

    1980-03-01

    Two 3-quasiparticle isomers with spins, parities and half lives of 19/2 + , 1.1 μ and 23/2 - , 1.2 ns have been identified at 1433 and 1766 keV in 175 Hf. A third isomer possibly 35/2 - with a 1.2 μs half-life is found at 3015 keV. The first two are characterised as a 7/2 + (633) neutron coupled to the known 6 + and 8 - 2-proton isomers of the core nuclei. Rotational bands based on the 3-qp isomers are highly perturbed, due to Coriolis mixing, and their structure is reproduced in a band mixing calculation. The energy depression of the 3-quasiparticle states relative to the 2-quasiproton core states is attributed mainly to the residual proton-neutron interaction, and possibly also to blocking effects through neutron admixtures

  1. Projected quasiparticle theory for molecular electronic structure

    Science.gov (United States)

    Scuseria, Gustavo E.; Jiménez-Hoyos, Carlos A.; Henderson, Thomas M.; Samanta, Kousik; Ellis, Jason K.

    2011-09-01

    We derive and implement symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations and apply them to the molecular electronic structure problem. All symmetries (particle number, spin, spatial, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. We show that the resulting method yields a comprehensive black-box treatment of static correlations with effective one-electron (mean-field) computational cost. The ensuing wave function is of multireference character and permeates the entire Hilbert space of the problem. The energy expression is different from regular HFB theory but remains a functional of an independent quasiparticle density matrix. All reduced density matrices are expressible as an integration of transition density matrices over a gauge grid. We present several proof-of-principle examples demonstrating the compelling power of projected quasiparticle theory for quantum chemistry.

  2. Non-equilibrium quasiparticle processes in superconductor tunneling structures

    International Nuclear Information System (INIS)

    Perold, W.J.

    1990-01-01

    A broad overview is presented of the phenomenon of superconductivity. The tunneling of quasiparticles in superconducter-insulator structures is described. Related non-equilibrium processes, such as superconductor bandgap suppresion, quasiparticle diffusion and recombination, and excess quasiparticle collection are discussed. The processes are illustrated with numerical computer simulation data. The importance of the inter-relationship between these processes in practical multiple tunneling junction superconducting device structures is also emphasized. 14 refs., 8 figs

  3. Quasi-particle electronic band structure and alignment of the V-VI-VII semiconductors SbSI, SbSBr, and SbSeI for solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Butler, Keith T. [Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom); McKechnie, Scott; Azarhoosh, Pooya; Schilfgaarde, Mark van [Department of Physics, Kings College London, London WC2R 2LS (United Kingdom); Scanlon, David O. [University College London, Kathleen Lonsdale Materials Chemistry, 20 Gordon Street, London WC1H 0AJ (United Kingdom); Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE (United Kingdom); Walsh, Aron, E-mail: a.walsh@bath.ac.uk [Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom); Global E" 3 Institute and Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of)

    2016-03-14

    The ternary V-VI-VII chalcohalides consist of one cation and two anions. Trivalent antimony—with a distinctive 5s{sup 2} electronic configuration—can be combined with a chalcogen (e.g., S or Se) and halide (e.g., Br or I) to produce photoactive ferroelectric semiconductors with similarities to the Pb halide perovskites. We report—from relativistic quasi-particle self-consistent GW theory—that these materials have a multi-valley electronic structure with several electron and hole basins close to the band extrema. We predict ionisation potentials of 5.3–5.8 eV from first-principles for the three materials, and assess electrical contacts that will be suitable for achieving photovoltaic action from these unconventional compounds.

  4. Measurements of quasiparticle tunneling dynamics in a band-gap-engineered transmon qubit.

    Science.gov (United States)

    Sun, L; DiCarlo, L; Reed, M D; Catelani, G; Bishop, Lev S; Schuster, D I; Johnson, B R; Yang, Ge A; Frunzio, L; Glazman, L; Devoret, M H; Schoelkopf, R J

    2012-06-08

    We have engineered the band gap profile of transmon qubits by combining oxygen-doped Al for tunnel junction electrodes and clean Al as quasiparticle traps to investigate energy relaxation due to quasiparticle tunneling. The relaxation time T1 of the qubits is shown to be insensitive to this band gap engineering. Operating at relatively low-E(J)/E(C) makes the transmon transition frequency distinctly dependent on the charge parity, allowing us to detect the quasiparticles tunneling across the qubit junction. Quasiparticle kinetics have been studied by monitoring the frequency switching due to even-odd parity change in real time. It shows the switching time is faster than 10  μs, indicating quasiparticle-induced relaxation has to be reduced to achieve T1 much longer than 100  μs.

  5. Signature splitting in two quasiparticle rotational bands of 180, 182 Ta

    Indian Academy of Sciences (India)

    quasiparticle rotor model. The phase as well as magnitudeof the experimentally observed signature splitting in K π = 1 + band of 180 Ta, which could not be explained in earlier calculations, is successfully reproduced. The conflict regarding placement of ...

  6. Identicity in high-K three quasiparticle rotational bands: a theoretical approach

    International Nuclear Information System (INIS)

    Kaur, Harjeet; Singh, Pardeep; Malik, Sham S

    2015-01-01

    The systematics are studied for the identical band phenomenon in high-K three quasiparticle rotational bands. The identical rotational bands based on the same bandhead spin are analyzed on the basis of similarities in γ-ray energies, dynamic moment of inertia and kinematic moment of inertia in particular, which is a function of deformation degrees of freedom, pairing strengths and Nilsson orbitals in nuclei. It is established that a combined effect of all these parameters decides the identicity of the moment of inertia in high-K three quasiparticle rotational bands as the systematics are backed by the Tilted Axis Cranking model calculations. (paper)

  7. Description of multi-quasiparticle bands by the tilted axis cranking model

    International Nuclear Information System (INIS)

    Frauendorf, S.

    2000-01-01

    The selfconsistent cranking approach is extended to the case of rotation about an axis which is tilted with respect to the principal axes of the deformed potential (Tilted Axis Cranking). Expressions for the energies and the intra bands electro-magnetic transition probabilities are given. The mean field solutions are interpreted in terms of quantal rotational states. The construction of the quasiparticle configurations and the elimination of spurious states is discussed. The application of the theory to high spin data is demonstrated by analyzing the multi-quasiparticle bands in the nuclides with N=102,103 and Z=71,72,73

  8. Marginal Fermi liquid and kink structure of quasiparticles in cuprates

    International Nuclear Information System (INIS)

    Kakehashi, Y.; Fulde, P.

    2007-01-01

    On the basis of the self-consistent projection operator method for nonlocal excitations, we show that a kink structure appears in the quasiparticle excitation spectrum of the two-dimensional Hubbard model at low doping concentrations. It is caused by a mixing between the quasiparticle state and the excitations with short-range antiferromagnetic order. The results explain the kink in high-T c cuprates

  9. Alignments of multi-quasiparticle bands and seniority-dependent reduced pairing

    International Nuclear Information System (INIS)

    Dracoulis, G.D.

    1994-09-01

    Pairing correlations in multi-quasiparticle states in deformed nuclei are expected to be reduced because of blocking. New intrinsic states and their associated rotational bands have been identified allowing comparisons to be made as a function of seniority and between nuclei. The possible effects of the reduced pairing on the collective rotation, and its manifestation in terms of alignment, are discussed. 13 refs., 2 figs

  10. Anisotropic energy-gaps of iron-based superconductivity from intra-band quasiparticle interference in LiFeAs

    Energy Technology Data Exchange (ETDEWEB)

    Rost, A.W. [LASSP, Department of Physics, Cornell, Ithaca, NY 14853 (United States); SUPA, School of Physics and Astronomy, Univ. of St Andrews, St Andrews, Fife KY16 9SS (United Kingdom); Allan, M.P. [LASSP, Department of Physics, Cornell, Ithaca, NY 14853 (United States); SUPA, School of Physics and Astronomy, Univ. of St Andrews, St Andrews, Fife KY16 9SS (United Kingdom); CMPMS Department, Brookhaven National Laboratory, Upton, NY 11973 (United States); Mackenzie, A.P. [SUPA, School of Physics and Astronomy, Univ. of St Andrews, St Andrews, Fife KY16 9SS (United Kingdom); Xie, Y. [CMPMS Department, Brookhaven National Laboratory, Upton, NY 11973 (United States); Davis, J.C. [LASSP, Department of Physics, Cornell, Ithaca, NY 14853 (United States); SUPA, School of Physics and Astronomy, Univ. of St Andrews, St Andrews, Fife KY16 9SS (United Kingdom); CMPMS Department, Brookhaven National Laboratory, Upton, NY 11973 (United States); Kavli Institute at Cornell for Nanoscale Science, Cornell, Ithaca, NY 14853 (United States); Kihou, K.; Lee, C.H.; Iyo, A.; Eisaki, H. [AIST, Tsukuba, Ibaraki 305-8568 (Japan); Chuang, T.M. [LASSP, Department of Physics, Cornell, Ithaca, NY 14853 (United States); CMPMS Department, Brookhaven National Laboratory, Upton, NY 11973 (United States); Inst. of Physics, Academica Sinica, Nankang, Taipei 11529, Taiwan (China)

    2012-07-01

    Cooper pairing in the Fe-based superconductors is thought to occur due to the projection of the antiferromagnetic interactions between iron atoms onto the complex momentum-space electronic structure. A key consequence is that distinct anisotropic energy gaps {Delta}{sub i}(k) with specific relative orientations should occur on the different electronic bands i. To determine this previously unresolved gap structure high-precision spectroscopy is required. Here we introduce the STM technique of intra-band Bogolyubov quasiparticle scattering interference (QPI) to iron-based superconductor studies, focusing on LiFeAs. We identify the QPI signatures of three hole-like dispersions and, by introducing a new QPI technique, determine the magnitude and relative orientations of corresponding anisotropic {Delta}{sub i}(k). Intra-band Bogolyubov QPI therefore yields the spectroscopic information required to identify the mechanism of superconductivity in Fe-based superconductors.

  11. Close near-degeneracy in a pair of four-quasiparticle bands in 194Tl

    International Nuclear Information System (INIS)

    Masiteng, P.L.; Lawrie, E.A.; Ramashidzha, T.M.; Bark, R.A.; Carlsson, B.G.; Lawrie, J.J.; Lindsay, R.; Komati, F.; Kau, J.; Maine, P.; Maliage, S.M.; Matamba, I.; Mullins, S.M.; Murray, S.H.T.; Mutshena, K.P.; Pasternak, A.A.; Ragnarsson, I.

    2013-01-01

    A pair of rotational bands associated with the πh 9/2 ⊗νi 13/2 −1 configuration at lower spins and with the πh 9/2 ⊗νi 13/2 −3 configuration at higher spins is found in 194 Tl. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. Such close near-degeneracy probably indicates chiral geometry in the angular momentum space

  12. Heavy-fermion quasiparticles in UPt3

    International Nuclear Information System (INIS)

    Taillefer, L.; Lonzarich, G.G.

    1988-01-01

    The quasiparticle band structure of the heavy-fermion superconductor UPt 3 has been investigated by means of angle-resolved measurements of the de Haas--van Alphen effect. Most of the results are consistent with a model of five quasiparticle bands at the Fermi level corresponding to Fermi surfaces similar to those calculated by band theory. However, as inferred from the extremely high cyclotron masses, the quasiparticle bands are much flatter than the calculated ones. The nature of the observed quasiparticles and their relationship to thermodynamic properties are briefly considered

  13. 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.

  14. 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

  15. Robust determination of the superconducting gap sign structure via quasiparticle interference

    Energy Technology Data Exchange (ETDEWEB)

    Altenfeld, Dustin [Institut fuer Theoretische Physik III, Ruhr-Universitaet Bochum, D-44801 Bochum (Germany); Hirschfeld, Peter [Department of Physics, University of Florida, Gainesville, Florida 32611 (United States); Eremin, Ilya [Institut fuer Theoretische Physik III, Ruhr-Universitaet Bochum, D-44801 Bochum (Germany); Kazan Federal University, Kazan 420008 (Russian Federation); Mazin, Igor [Naval Research Laboratory, Code 6393, Washington, DC 20375 (United States)

    2016-07-01

    Using an electronic theory, we present a qualitative description to identify sign changes of the superconducting order parameter via quasiparticle interference (QPI) measurement in Fe-based superconductors (FeSc). In particular, we point out that the temperature dependence of the momentum-integrated QPI data can be used to differentiate between s{sub +-} and s{sub ++} states in a system with typical iron pnictide Fermi surface. We show that the signed symmetrized and antisymmetrized QPI maps are useful to obtain a characteristic signature of a gap sign change or lack thereof, starting from two-band model up to ab initio based band structure calculation. We further suggest this method as a robust way of the determination of the superconducting gap sign structure in experiment and discuss its application to the LiFeAs compounds.

  16. Structure of quasiparticles and their fusion algebra in fractional quantum Hall states

    Science.gov (United States)

    Barkeshli, Maissam; Wen, Xiao-Gang

    2009-05-01

    It was recently discovered that fractional quantum Hall (FQH) states can be characterized quantitatively by the pattern of zeros that describe how the ground-state wave function goes to zero when electrons are brought close together. Quasiparticles in the FQH states can be described in a similar quantitative way by the pattern of zeros that result when electrons are brought close to the quasiparticles. In this paper, we combine the pattern of zeros approach and the conformal field theory (CFT) approach to calculate the topological properties of quasiparticles. We discuss how the quasiparticles in FQH states naturally form representations of a magnetic translation algebra, with members of a representation differing from each other by Abelian quasiparticles. We find that this structure dramatically simplifies topological properties of the quasiparticles, such as their fusion rules, charges, and scaling dimensions, and has consequences for the ground state degeneracy of FQH states on higher genus surfaces. We find constraints on the pattern of zeros of quasiparticles that can fuse together, which allow us to derive the fusion rules of quasiparticles from their pattern of zeros, at least in the case of the (generalized and composite) parafermion states. We also calculate from CFT the number of quasiparticle types in the generalized and composite parafermion states, which confirm the result obtained previously through a completely different approach.

  17. Structure of quasiparticles and their fusion algebra in fractional quantum Hall states

    International Nuclear Information System (INIS)

    Barkeshli, Maissam; Wen Xiaogang

    2009-01-01

    It was recently discovered that fractional quantum Hall (FQH) states can be characterized quantitatively by the pattern of zeros that describe how the ground-state wave function goes to zero when electrons are brought close together. Quasiparticles in the FQH states can be described in a similar quantitative way by the pattern of zeros that result when electrons are brought close to the quasiparticles. In this paper, we combine the pattern of zeros approach and the conformal field theory (CFT) approach to calculate the topological properties of quasiparticles. We discuss how the quasiparticles in FQH states naturally form representations of a magnetic translation algebra, with members of a representation differing from each other by Abelian quasiparticles. We find that this structure dramatically simplifies topological properties of the quasiparticles, such as their fusion rules, charges, and scaling dimensions, and has consequences for the ground state degeneracy of FQH states on higher genus surfaces. We find constraints on the pattern of zeros of quasiparticles that can fuse together, which allow us to derive the fusion rules of quasiparticles from their pattern of zeros, at least in the case of the (generalized and composite) parafermion states. We also calculate from CFT the number of quasiparticle types in the generalized and composite parafermion states, which confirm the result obtained previously through a completely different approach.

  18. Band structures in near spherical 138Ce

    Science.gov (United States)

    Bhattacharjee, T.; Chanda, S.; Bhattacharyya, S.; Basu, S. K.; Bhowmik, R. K.; Das, J. J.; Pramanik, U. Datta; Ghugre, S. S.; Madhavan, N.; Mukherjee, A.; Mukherjee, G.; Muralithar, S.; Singh, R. P.

    2009-06-01

    The high spin states of N=80138Ce have been populated in the fusion evaporation reaction 130Te( 12C, 4n) 138Ce at E=65 MeV. The γ transitions belonging to various band structures were detected and characterized using an array of five Clover Germanium detectors. The level scheme has been established up to a maximum spin and excitation energy of 23 ℏ and 9511.3 keV, respectively, by including 53 new transitions. The negative parity ΔI=1 band, developed on the 6536.3 keV 15 level, has been conjectured to be a magnetic rotation band following a semiclassical analysis and comparing the systematics of similar bands in the neighboring nuclei. The said band is proposed to have a four quasiparticle configuration of [πgh]⊗[. Other band structures are interpreted in terms of multi-quasiparticle configurations, based on Total Routhian Surface (TRS) calculations. For the low and medium spin states, a shell model calculation using a realistic two body interaction has been performed using the code OXBASH.

  19. Direct imaging of band profile in single layer MoS2 on graphite: quasiparticle energy gap, metallic edge states, and edge band bending.

    Science.gov (United States)

    Zhang, Chendong; Johnson, Amber; Hsu, Chang-Lung; Li, Lain-Jong; Shih, Chih-Kang

    2014-05-14

    Using scanning tunneling microscopy and spectroscopy, we probe the electronic structures of single layer MoS2 on graphite. The apparent quasiparticle energy gap of single layer MoS2 is measured to be 2.15 ± 0.06 eV at 77 K, albeit a higher second conduction band threshold at 0.2 eV above the apparent conduction band minimum is also observed. Combining it with photoluminescence studies, we deduce an exciton binding energy of 0.22 ± 0.1 eV (or 0.42 eV if the second threshold is use), a value that is lower than current theoretical predictions. Consistent with theoretical predictions, we directly observe metallic edge states of single layer MoS2. In the bulk region of MoS2, the Fermi level is located at 1.8 eV above the valence band maximum, possibly due to the formation of a graphite/MoS2 heterojunction. At the edge, however, we observe an upward band bending of 0.6 eV within a short depletion length of about 5 nm, analogous to the phenomena of Fermi level pinning of a 3D semiconductor by metallic surface states.

  20. 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...

  1. Investigation of the two-quasiparticle bands in the doubly-odd nucleus 166Ta using a particle-number conserving cranked shell model

    Science.gov (United States)

    Zhang, ZhenHua

    2016-07-01

    The high-spin rotational properties of two-quasiparticle bands in the doubly-odd 166Ta are analyzed using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the blocking effects are taken into account exactly. The experimental moments of inertia and alignments and their variations with the rotational frequency hω are reproduced very well by the particle-number conserving calculations, which provides a reliable support to the configuration assignments in previous works for these bands. The backbendings in these two-quasiparticle bands are analyzed by the calculated occupation probabilities and the contributions of each orbital to the total angular momentum alignments. The moments of inertia and alignments for the Gallagher-Moszkowski partners of these observed two-quasiparticle rotational bands are also predicted.

  2. Experimental estimates of quasiparticle interactions for rotational nuclei

    International Nuclear Information System (INIS)

    Frauendorf, S.; Riedinger, L.L.

    1984-01-01

    Previously presented data on rotationally aligned quasiparticle bands in sup(160,161,162,163)Yb are analyzed to give experimental values of the quasiparticle interactions Vsub(μν) as a function of rotational frequency. The measured level energies are converted to the rotating frame of reference and expressed as routhians. The routhian of a multi-quasiparticle band is compared to the sum of the routhians of the component quasiparticles at a given frequency, the difference being the quasiparticle interaction. The experimental spectra of bands in these nuclei are consistent with the assumption of a binary interaction between the rotating quasiparticles, where most of the Vsub(μν) are in the range -0.3 to -0.1 MeV. Analysis of the shift in the observed crossing frequencies for bands of different quasiparticle number yields similar values. The extracted Vsub(μν) are found to have a frequency dependence, which is associated with the loss of alignment of a multi-quasiparticle state. An equidistant-level model is used to estimate the contributions to the quasiparticle interactions by polarization of the collective degrees of freedom. This model yields typical Vsub(μν) values of -0.15 MeV, which is only half of some values extracted from experiment. This suggests that the extracted Vsub(μν) contain a significant amount of nuclear-structure information. (orig.)

  3. Quasi-particle excitations and dynamical structure function of trapped Bose-condensates in the WKB approximation

    OpenAIRE

    Csordás, András; Graham, Robert; Szépfalusy, Péter

    1997-01-01

    The Bogoliubov equations of the quasi-particle excitations in a weakly interacting trapped Bose-condensate are solved in the WKB approximation in an isotropic harmonic trap, determining the discrete quasi-particle energies and wave functions by torus (Bohr-Sommerfeld) quantization of the integrable classical quasi-particle dynamics. The results are used to calculate the position and strengths of the peaks in the dynamic structure function which can be observed by off-resonance inelastic light...

  4. Band structure in 104Ag

    International Nuclear Information System (INIS)

    Goswami, A.; Saha Sarkar, M.; Datta Pramanik, U.; Banerjee, P.; Basu, P.; Bhattacharya, P.; Bhattacharya, S.; Chatterjee, M.L.; Sen, S.; Dasmahapatra, B.

    1995-01-01

    The level structure of 104 Ag has been studied through the 103 Rh(α,3nγ) reaction at E α =40 and 45 MeV. The principal features of the proposed level scheme are in agreement with those obtained earlier through heavy ion reaction. A two-quasiparticle-plus-rotor model calculation has been performed, and the results are compared with experimental data. (orig.)

  5. Shell structure effects at high excitations and many-quasiparticle configurations

    International Nuclear Information System (INIS)

    Soloviev, V.G.

    1980-01-01

    Experimental and theoretical data available on few- and many-quasiparticle components of the wave functions of complex nuclei at low, intermediate and high energies are shortly analyzed. The components are treated in the nuclear quasiparticle-phonon model. Specific features of the lowest and high-spin states, giant resonances, neutron resonances and the effects of the energy-level structure in the few-and many-particle transfer reactions are discussed. It is concluded that the most reliable nuclear properties are determined by the components, their behaviour reflecting the shell structure effects. Wich increasing excitation energy the density of levels increases exponentially and the contribution of few-quasiparticle components to the normalization of the wave functions decreases exponentially

  6. Self-energies, renormalization factor, Luttinger sum rule and quasiparticle structure of the Hubbard systems

    International Nuclear Information System (INIS)

    Lopez-Aguilar, F.; Costa-Quintana, J.

    1992-01-01

    In this paper, the authors give a method for obtaining the renormalized electronic structure of the Hubbard systems. The first step is the determination of the self-energy beyond the Hartree-Fock approximation. This self-energy is constructed from several dielectric response functions. The second step is the determination of the quasiparticle band structure calculation which is performed from an appropriate modification of the augmented plane wave method. The third step consists in the determination of the renormalized density of states deduced from the spectral functions. The analysis of the renormalized density of states of the strongly correlated systems leads to the conclusion that there exist three types of resonances in their electronic structures, the lower energy resonances (LER), the middle energy resonances (MER) and the upper energy resonances (UER). In addition, the authors analyze the conditions for which the Luttinger theorem is satisfied. All of these questions are determined in a characteristic example which allows to test the theoretical method

  7. Optically Discriminating Carrier-Induced Quasiparticle Band Gap and Exciton Energy Renormalization in Monolayer MoS_{2}.

    Science.gov (United States)

    Yao, Kaiyuan; Yan, Aiming; Kahn, Salman; Suslu, Aslihan; Liang, Yufeng; Barnard, Edward S; Tongay, Sefaattin; Zettl, Alex; Borys, Nicholas J; Schuck, P James

    2017-08-25

    Optoelectronic excitations in monolayer MoS_{2} manifest from a hierarchy of electrically tunable, Coulombic free-carrier and excitonic many-body phenomena. Investigating the fundamental interactions underpinning these phenomena-critical to both many-body physics exploration and device applications-presents challenges, however, due to a complex balance of competing optoelectronic effects and interdependent properties. Here, optical detection of bound- and free-carrier photoexcitations is used to directly quantify carrier-induced changes of the quasiparticle band gap and exciton binding energies. The results explicitly disentangle the competing effects and highlight longstanding theoretical predictions of large carrier-induced band gap and exciton renormalization in two-dimensional semiconductors.

  8. Optically Discriminating Carrier-Induced Quasiparticle Band Gap and Exciton Energy Renormalization in Monolayer MoS2

    Science.gov (United States)

    Yao, Kaiyuan; Yan, Aiming; Kahn, Salman; Suslu, Aslihan; Liang, Yufeng; Barnard, Edward S.; Tongay, Sefaattin; Zettl, Alex; Borys, Nicholas J.; Schuck, P. James

    2017-08-01

    Optoelectronic excitations in monolayer MoS2 manifest from a hierarchy of electrically tunable, Coulombic free-carrier and excitonic many-body phenomena. Investigating the fundamental interactions underpinning these phenomena—critical to both many-body physics exploration and device applications—presents challenges, however, due to a complex balance of competing optoelectronic effects and interdependent properties. Here, optical detection of bound- and free-carrier photoexcitations is used to directly quantify carrier-induced changes of the quasiparticle band gap and exciton binding energies. The results explicitly disentangle the competing effects and highlight longstanding theoretical predictions of large carrier-induced band gap and exciton renormalization in two-dimensional semiconductors.

  9. Temperature dependent quasiparticle renormalization in nickel metal

    Energy Technology Data Exchange (ETDEWEB)

    Ovsyannikov, Ruslan; Sanchez-Barriga, Jaime; Fink, Joerg; Duerr, Hermann A. [Helmholtz Zentrum Berlin (Germany). BESSY II

    2009-07-01

    One of the fundamental consequences of electron correlation effects is that the bare particles in solids become 'dressed', i.e. they acquire an increased effective mass and a lifetime. We studied the spin dependent quasiparticle band structure of Ni(111) with high resolution angle resolved photoemission spectroscopy. At low temperatures (50 K) a renormalization of quasiparticle energy and lifetime indicative of electron-phonon coupling is observed in agreement with literature. With increasing temperature we observe a decreasing quasiparticle lifetime at the Fermi level for all probed minority spin bands as expected from electron phonon coupling. Surprisingly the majority spin states behave differently. We actually observe a slightly increased lifetime at room temperature. The corresponding increase in Fermi velocity points to a temperature dependent reduction of the majority spin quasiparticle renormalization.

  10. Recursion method for the quasiparticle structure of a single vortex with induced magnetic order

    DEFF Research Database (Denmark)

    Udby, L.; Andersen, B.M.; Hedegård, P.

    2006-01-01

    . Furthermore, we study the low-energy quasiparticle structure when magnetic vortices operate as pinning centers for surrounding unidirectional spin density waves (stripes). We calculate the Fourier transformed LDOS and show how the energy dependence of relevant Fourier components can be used to determine...

  11. Electronic band structure

    International Nuclear Information System (INIS)

    Grosso, G.

    1986-01-01

    The aim of this chapter is to present, in detail, some theoretical methods used to calculate electronic band structures in crystals. The basic strategies employed to attack the problem of electronic-structure calculations are presented. Successive sections present the basic formulations of the tight-binding, orthogonalized-plane-wave, Green'sfunction, and pseudopotential methods with a discussion of their application to perfect solids. Exemplifications in the case of a few selected problems provide further insight by the author into the physical aspects of the different methods and are a guide to the use of their mathematical techniques. A discussion is offered of completely a priori Hartree-Fock calculations and attempts to extend them. Special aspects of the different methods are also discussed in light of recently published related work

  12. Collective states in 230Th: band structure

    Directory of Open Access Journals (Sweden)

    A. I. Levon

    2009-12-01

    Full Text Available Experimental data for the excited states in the deformed nucleus 230Th studied in the (p, t reaction are analyzed. Sequences of the states are selected which can be treated as rotational bands and as multiplets of excitations. Experimental data are compared with the interacting boson model (IBM and the quasiparticle-phonon model (QPM calculations.

  13. Two- and four-quasiparticle states in the interacting boson model: Strong-coupling and decoupled band patterns in the SU(3) limit

    International Nuclear Information System (INIS)

    Vretenar, D.; Paar, V.; Bonsignori, G.; Savoia, M.

    1990-01-01

    An extension of the interacting boson approximation model is proposed by allowing for two- and four-quasiparticle excitations out of the boson space. The formation of band patterns based on two- and four-quasiparticle states is investigated in the SU(3) limit of the model. For hole-type (particle-type) fermions coupled to the SU(3) prolate (oblate) core, it is shown that the algebraic K-representation basis, which is the analog of the strong-coupling basis of the geometrical model, provides an appropriate description of the low-lying two-quasiparticle bands. In the case of particle-type (hole-type) fermions coupled to the SU(3) prolate (oblate) core, a new algebraic decoupling basis is derived that is equivalent in the geometrical limit to Stephens' rotation-aligned basis. Comparing the wave functions that are obtained by diagonalization of the model Hamiltonian to the decoupling basis, several low-lying two-quasiparticle bands are identified. The effects of an interaction that conserves only the total nucleon number, mixing states with different number of fermions, are investigated in both the strong-coupling and decoupling limits. All calculations are performed for an SU(3) boson core and the h11/2 fermion orbital

  14. Superdeformed bands of odd nuclei in A=190 region in the quasiparticle picture

    International Nuclear Information System (INIS)

    Terasaki, J.; Flocard, H.; Heenen, P.H.; Bonche, P.

    1996-07-01

    Properties of the superdeformed (SD) bands of 195 Pb and 193 Hg have been studied by the cranked Hartree-Fock-Bogoliubov method. The calculations reproduce the flat behavior of the dynamical moment of inertia of two of the SD bands of 195 Pb measured recently. Possible configuration assignments for the observed bands 3 and 4 of 195 Pb are discussed. The two interacting SD bands of 193 Hg have also been calculated. The analysis confirms the superiority of a density-dependent pairing force over a seniority pairing interaction. (author)

  15. Quasiparticle GW calculations within the GPAW electronic structure code

    DEFF Research Database (Denmark)

    Hüser, Falco

    The GPAW electronic structure code, developed at the physics department at the Technical University of Denmark, is used today by researchers all over the world to model the structural, electronic, optical and chemical properties of materials. They address fundamental questions in material science...... and use their knowledge to design new materials for a vast range of applications. Todays hottest topics are, amongst many others, better materials for energy conversion (e.g. solar cells), energy storage (batteries) and catalysts for the removal of environmentally dangerous exhausts. The mentioned...... properties are to a large extent governed by the physics on the atomic scale, that means pure quantum mechanics. For many decades, Density Functional Theory has been the computational method of choice, since it provides a fairly easy and yet accurate way of determining electronic structures and related...

  16. Theoretical study of band structure of odd-mass {sup 115,117}I isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Dhanvir, E-mail: singh1472phy@gmail.com; Kumar, Amit, E-mail: akbcw2@gmail.com; Sharma, Chetan, E-mail: chetan24101985@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-184101 (India); Bharti, Arun, E-mail: arunbharti-2003@yahoo.co.in [Professor, Department of Physics and Electronics, University of Jammu, Jammu-180006 (India)

    2016-05-06

    By using the microscopic approach of Projected Shell Model (PSM), negative-parity band structures of odd mass neutron-rich {sup 115,117}I 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.

  17. Strongly correlated electron materials. I. Theory of the quasiparticle structure

    International Nuclear Information System (INIS)

    Lopez-Aguilar, F.; Costa-Quintana, J.; Puig-Puig, L.

    1993-01-01

    In this paper we give a method for analyzing the renormalized electronic structure of the Hubbard systems. The first step is the determination of effective interactions from the random-phase approximation (RPA) and from an extended RPA (ERPA) that introduces vertex effects within the bubble polarization. The second step is the determination of the density of states deduced from the spectral functions. Its analysis leads us to conclude that these systems can exhibit three types of resonances in their electronic structures: the lower-, middle-, and upper-energy resonances. Furthermore, we analyze the conditions for which there is only one type of resonance and the causes that lead to the disappearance of the heavy-fermion state. We finally introduce the RPA and ERPA effective interactions within the strong-coupling theory and we give the conditions for obtaining coupling and superconductivity

  18. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe2.

    Science.gov (United States)

    Arguello, C J; Rosenthal, E P; Andrade, E F; Jin, W; Yeh, P C; Zaki, N; Jia, S; Cava, R J; Fernandes, R M; Millis, A J; Valla, T; Osgood, R M; Pasupathy, A N

    2015-01-23

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe2 that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe2. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe2, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.

  19. Intrinsic properties of high-spin band structures in triaxial nuclei

    Science.gov (United States)

    Jehangir, S.; Bhat, G. H.; Sheikh, J. A.; Palit, R.; Ganai, P. A.

    2017-12-01

    The band structures of 68,70Ge, 128,130,132,134Ce and 132,134,136,138Nd are investigated using the triaxial projected shell model (TPSM) approach. These nuclei depict forking of the ground-state band into several s-bands and in some cases, both the lowest two observed s-bands depict neutron or proton character. It was discussed in our earlier work that this anomalous behaviour can be explained by considering γ-bands based on two-quasiparticle configurations. As the parent band and the γ-band built on it have the same intrinsic structure, g-factors of the two bands are expected to be similar. In the present work, we have undertaken a detailed investigation of g-factors for the excited band structures of the studied nuclei and the available data for a few high-spin states are shown to be in fair agreement with the predicted values.

  20. Band structure and Fermi surface of UPd2Al3 studied by angle-resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    Fujimori, Shin-ichi; Saitoh, Yuji; Okane, Tetsuo; Yamagami, Hiroshi; Fujimori, Atsushi; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika

    2007-01-01

    We have observed the band structure and Fermi surfaces of the heavy Fermion superconductor UPd 2 Al 3 by angle-resolved photoemission experiments in the soft X-ray region. We observed renormalized quasi-particle bands in the vicinity of the Fermi level and strongly dispersive bands on the higher binding energy side. Our observation suggests that the structure previously assigned to contributions from localized states in the U 5f spectrum has strong energy dispersions

  1. Quasiparticle and optical properties of strained stanene and stanane.

    Science.gov (United States)

    Lu, Pengfei; Wu, Liyuan; Yang, Chuanghua; Liang, Dan; Quhe, Ruge; Guan, Pengfei; Wang, Shumin

    2017-06-20

    Quasiparticle band structures and optical properties of two dimensional stanene and stanane (fully hydrogenated stanene) are studied by the GW and GW plus Bethe-Salpeter equation (GW-BSE) approaches, with inclusion of the spin-orbit coupling (SOC). The SOC effect is significant for the electronic and optical properties in both stanene and stanane, compared with their group IV-enes and IV-anes counterparts. Stanene is a semiconductor with a quasiparticle band gap of 0.10 eV. Stanane has a sizable band gap of 1.63 eV and strongly binding exciton with binding energy of 0.10 eV. Under strain, the quasiparticle band gap and optical spectrum of both stanene and stanane are tunable.

  2. Structure of two-, four-, and six-quasiparticle isomers in 174Yb and K-forbidden decays

    Science.gov (United States)

    Dracoulis, G. D.; Lane, G. J.; Kondev, F. G.; Byrne, A. P.; Kibédi, T.; Watanabe, H.; Ahmad, I.; Carpenter, M. P.; Freeman, S. J.; Janssens, R. V.; Hammond, N. J.; Lauritsen, T.; Lister, C. J.; Mukherjee, G.; Seweryniak, D.; Chowdhury, P.; Tandel, S. K.

    2005-04-01

    The stable nucleus 174Yb has been studied using deep-inelastic reactions and time-correlated γ-ray spectroscopy. New intrinsic states assigned include a 370-ns isomer at 1765 keV, which we associate with a predicted Kπ=7- two-quasineutron configuration. Analysis of the alignment and in-band properties of its rotational band, identified using time-correlated coincidences, allows characterization of the configuration. The properties of a newly identified rotational band built on the known 830-μs isomer at 1518 keV support the 6+, 2-quasineutron configuration assignment proposed previously. The 6+ band is fed by a four-quasiparticle, Kπ=14+ isomer at 3699 keV and several higher multiquasiparticle states, including a six-quasiparticle isomer at 6147 keV with K=(22,23). The results are discussed in terms of the states predicted on the basis of multiquasiparticle calculations. The anomalously fast K-forbidden transition strengths from the 14+ isomer are attributed to either K mixing in the neutron configuration or to random mixing in the high-level-density region. The 7- isomer decays are not abnormal, whereas the very hindered E2 transition from the 6+ isomer to the ground-state band remains unexplained.

  3. Quasiparticle structure and coherent propagation in the t-Jz-Jperpendicular model

    International Nuclear Information System (INIS)

    Gan, J.; Hedegard, P.

    1996-01-01

    Numerical studies, from variational calculation to exact diagonalization, all indicate that the quasiparticle generated by introducing one hole into a two-dimensional quantum antiferromagnet has the same nature as a string state in the t-J z model. Based on this observation, we attempt to visualize the quasiparticle formation and subsequent coherent propagation at low energy by studying the generalized t-J z -J perpendicular model in which we first diagonalize the t-J z model and then perform a degenerate perturbation in J perpendicular . We construct the quasiparticle state and derive an effective Hamiltonian describing the coherent propagation of the quasiparticle and its interaction with the spin wave excitations in the presence of the Nacute eel order. We expect that qualitative properties of the quasiparticle remain intact when analytically continuing J perpendicular from the anisotropic J perpendicular z to the isotropic J perpendicular =J z limit, despite the fact that the spin wave excitations change from gapful to gapless. Extrapolating to J perpendicular =J z , our quasiparticle dispersion and spectral weight compare well with the exact numerical results for small clusters. copyright 1996 The American Physical Society

  4. Interpretation of quarks having fractional quantum numbers as structural quasi-particles by means of the composite model with integral quantum numbers

    International Nuclear Information System (INIS)

    Tyapkin, A.A.

    1976-01-01

    The problem is raised on the interpretation of quarks having fractional quantum numbers as structural quasi-particles. A new composite model is proposed on the basis of the fundamental triplet representation of fermions having integral quantum numbers

  5. Photonic band gap structure simulator

    Science.gov (United States)

    Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.

    2006-10-03

    A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.

  6. Location of the valence band maximum in the band structure of anisotropic 1 T'-ReSe2

    Science.gov (United States)

    Eickholt, P.; Noky, J.; Schwier, E. F.; Shimada, K.; Miyamoto, K.; Okuda, T.; Datzer, C.; Drüppel, M.; Krüger, P.; Rohlfing, M.; Donath, M.

    2018-04-01

    Transition-metal dichalcogenides (TMDCs) are a focus of current research due to their fascinating optical and electronic properties with possible technical applications. ReSe2 is an interesting material of the TMDC family, with unique anisotropic properties originating from its distorted 1 T structure (1 T '). To develop a fundamental understanding of the optical and electric properties, we studied the underlying electronic structure with angle-resolved photoemission (ARPES) as well as band-structure calculations within the density functional theory (DFT)-local density approximation (LDA) and GdW approximations. We identified the Γ ¯M¯1 direction, which is perpendicular to the a axis, as a distinct direction in k space with the smallest bandwidth of the highest valence band. Using photon-energy-dependent ARPES, two valence band maxima are identified within experimental limits of about 50 meV: one at the high-symmetry point Z , and a second one at a non-high-symmetry point in the Brillouin zone. Thus, the position in k space of the global valence band maximum is undecided experimentally. Theoretically, an indirect band gap is predicted on a DFT-LDA level, while quasiparticle corrections lead to a direct band gap at the Z point.

  7. Complex band structure and electronic transmission eigenchannels

    DEFF Research Database (Denmark)

    Jensen, Anders; Strange, Mikkel; Smidstrup, Soren

    2017-01-01

    and complex band structure, in this case individual eigenchannel transmissions and different complex bands. We present calculations of decay constants for the two most conductive states as determined by complex band structure and standard DFT Landauer transport calculations for one semi-conductor and two...

  8. Quasiparticle self-consistent GW theory of III-V nitride semiconductors: Bands, gap bowing, and effective masses

    DEFF Research Database (Denmark)

    Svane, Axel; Christensen, Niels Egede; Gorczyca, I.

    2010-01-01

    on the basis of the local approximation to density functional theory, although generally overestimated by 0.2–0.3 eV in comparison with experimental gap values. Details of the electronic energies and the effective masses including their pressure dependence are compared with available experimental information....... The band gap of InGaN2 is considerably smaller than what would be expected by linear interpolation implying a significant band gap bowing in InGaN alloys....

  9. Quasiparticle Interference Studies of Quantum Materials.

    Science.gov (United States)

    Avraham, Nurit; Reiner, Jonathan; Kumar-Nayak, Abhay; Morali, Noam; Batabyal, Rajib; Yan, Binghai; Beidenkopf, Haim

    2018-06-03

    Exotic electronic states are realized in novel quantum materials. This field is revolutionized by the topological classification of materials. Such compounds necessarily host unique states on their boundaries. Scanning tunneling microscopy studies of these surface states have provided a wealth of spectroscopic characterization, with the successful cooperation of ab initio calculations. The method of quasiparticle interference imaging proves to be particularly useful for probing the dispersion relation of the surface bands. Herein, how a variety of additional fundamental electronic properties can be probed via this method is reviewed. It is demonstrated how quasiparticle interference measurements entail mesoscopic size quantization and the electronic phase coherence in semiconducting nanowires; helical spin protection and energy-momentum fluctuations in a topological insulator; and the structure of the Bloch wave function and the relative insusceptibility of topological electronic states to surface potential in a topological Weyl semimetal. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. High-energy band structure of gold

    DEFF Research Database (Denmark)

    Christensen, N. Egede

    1976-01-01

    The band structure of gold for energies far above the Fermi level has been calculated using the relativistic augmented-plane-wave method. The calculated f-band edge (Γ6-) lies 15.6 eV above the Fermi level is agreement with recent photoemission work. The band model is applied to interpret...

  11. Equation of motion method to describe quasiparticle structures in transitional and deformed nuclei

    International Nuclear Information System (INIS)

    Doenau, F.

    1985-01-01

    The development of the experimental techniques will supply one with more and more complete level schemes and transition matrix elements. This is a great challenge for the theorists to put the right questions and to work out the models accordingly. In this respect the method of equation of motion (EQM) seems to be a sulitable approach the inherent possibilities of which are yet not fully explored. The EQM is sketched for the case of one-quasiparticle (1qp) excitation in odd-mass nuclei. The coupling of a particle to the quasrupole and pair field is treated using the IBA for the collective degrees of freedom. Physical implications are shortly discussed. The selfconsistent aspects of the theory are considered. A perturbational treatment is proposed to construct the physical subspace that is necessary to perform selfconsistent calculations of the collective core energies. The EQM is formulated for the two-quasiparticle (2qp) excitations in transitional nuclei inclusive the coupling to the collective excitations (0 qp space). EQM can be widely applied to describe the complicated interplay between collective degrees of freedom and quasiparticle configurations are concluded

  12. Dynamical corrections to density-functional theory for quasiparticles in ferromagnetic 4f systems. I. T = 0 results for EuO

    International Nuclear Information System (INIS)

    Nolting, W.; Borstel, G.; Borgiel, W.

    1987-01-01

    A theory for the electronic quasiparticle spectrum of ferromagnetic 4f systems is presented and applied to the semiconductor EuO. The starting point is a d-f exchange model, which we solve exactly for T = 0. One of the results is a simple relationship between the spin-up quasiparticle energies and the ''free'' Bloch energies epsilon-c/sub m/(k), which we use to fix the epsilon-c/sub m/(k) in a highly realistic manner by performing a new self-consistent spin-polarized band-structure calculation based on density-functional theory. With the so-determined Bloch energies we investigate the spin-down quasiparticle spectrum, which exhibits even at T = 0 strong many-body effects as a consequence of spin-exchange processes between localized magnetic 4f moments and itinerant conduction electrons. We discuss in detail the spin-down quasiparticle spectral density for the ΓL direction, which should be observable in an inverse photoemission experiment. The shape of this function is strongly k dependent, revealing different types of quasiparticles. The prominent quasiparticle peaks in the spin-down quasiparticle spectral density are used to construct a quasiparticle band structure, which shows some striking deviations from the one-particle solution of the density-functional theory. Furthermore, results for the electronic self-energy and the quasiparticle density of states are presented

  13. The cellular approach to band structure calculations

    International Nuclear Information System (INIS)

    Verwoerd, W.S.

    1982-01-01

    A short introduction to the cellular approach in band structure calculations is given. The linear cellular approach and its potantial applicability in surface structure calculations is given some consideration in particular

  14. Trojan quasiparticles

    International Nuclear Information System (INIS)

    Gertjerenken, Bettina; Holthaus, Martin

    2014-01-01

    We argue that a time-periodically driven bosonic Josephson junction supports stable, quasiparticle-like collective response modes which are N-particle analogs of the nonspreading Trojan wave packets known from microwave-driven Rydberg atoms. Similar to their single-particle counterparts, these collective modes, dubbed ‘flotons’, are well described by a Floquet–Mathieu approximation, and possess a well-defined discrete set of excitations. In contrast to other, ‘chaotic’ modes of response, the nonheating Trojan modes conform to a mean-field description, and thus may be of particular interest for the more general question under which conditions the reduction of quantum N-particle dynamics to a strongly simplified mean-field evolution is feasible. Our reasoning is supported by phase-space portraits which reveal the degree of correspondence beween the N-particle dynamics und the mean-field picture in an intuitive manner. (paper)

  15. Quasiparticle interference in unconventional 2D systems.

    Science.gov (United States)

    Chen, Lan; Cheng, Peng; Wu, Kehui

    2017-03-15

    At present, research of 2D systems mainly focuses on two kinds of materials: graphene-like materials and transition-metal dichalcogenides (TMDs). Both of them host unconventional 2D electronic properties: pseudospin and the associated chirality of electrons in graphene-like materials, and spin-valley-coupled electronic structures in the TMDs. These exotic electronic properties have attracted tremendous interest for possible applications in nanodevices in the future. Investigation on the quasiparticle interference (QPI) in 2D systems is an effective way to uncover these properties. In this review, we will begin with a brief introduction to 2D systems, including their atomic structures and electronic bands. Then, we will discuss the formation of Friedel oscillation due to QPI in constant energy contours of electron bands, and show the basic concept of Fourier-transform scanning tunneling microscopy/spectroscopy (FT-STM/STS), which can resolve Friedel oscillation patterns in real space and consequently obtain the QPI patterns in reciprocal space. In the next two parts, we will summarize some pivotal results in the investigation of QPI in graphene and silicene, in which systems the low-energy quasiparticles are described by the massless Dirac equation. The FT-STM experiments show there are two different interference channels (intervalley and intravalley scattering) and backscattering suppression, which associate with the Dirac cones and the chirality of quasiparticles. The monolayer and bilayer graphene on different substrates (SiC and metal surfaces), and the monolayer and multilayer silicene on a Ag(1 1 1) surface will be addressed. The fifth part will introduce the FT-STM research on QPI in TMDs (monolayer and bilayer of WSe 2 ), which allow us to infer the spin texture of both conduction and valence bands, and present spin-valley coupling by tracking allowed and forbidden scattering channels.

  16. GW quasiparticle bandgaps of anatase TiO2 starting from DFT + U.

    Science.gov (United States)

    Patrick, Christopher E; Giustino, Feliciano

    2012-05-23

    We investigate the quasiparticle band structure of anatase TiO(2), a wide gap semiconductor widely employed in photovoltaics and photocatalysis. We obtain GW quasiparticle energies starting from density-functional theory (DFT) calculations including Hubbard U corrections. Using a simple iterative procedure we determine the value of the Hubbard parameter yielding a vanishing quasiparticle correction to the fundamental bandgap of anatase TiO(2). The bandgap (3.3 eV) calculated using this optimal Hubbard parameter is smaller than the value obtained by applying many-body perturbation theory to standard DFT eigenstates and eigenvalues (3.7 eV). We extend our analysis to the rutile polymorph of TiO(2) and reach similar conclusions. Our work highlights the role of the starting non-interacting Hamiltonian in the calculation of GW quasiparticle energies in TiO(2) and suggests an optimal Hubbard parameter for future calculations.

  17. GW correlation effects on plutonium quasiparticle energies: Changes in crystal-field splitting

    DEFF Research Database (Denmark)

    Chantis, A.N.; Albers, R.C.; Svane, Axel

    2009-01-01

    We present results for the electronic structure of plutonium by using a recently developed quasiparticle self-consistent GW method (QSGW). We consider a paramagnetic solution without spin-orbit interaction as a function of volume for the face-centred cubic (fcc) unit cell. We span unit-cell volumes...... ranging from 10% greater than the equilibrium volume of the δ phase to 90% of the equivalent for the α phase of Pu. The selfconsistent GW quasiparticle energies are compared to those obtained within the Local Density Approximation (LDA). The goal of the calculations is to understand systematic trends...... in the effects of electronic correlations on the quasiparticle energy bands of Pu as a function of the localisation of the f orbitals. We show that correlation effects narrow the f bands in two significantly different ways. Besides the expected narrowing of individual f bands (flatter dispersion), we find...

  18. Quasi-particle energies and optical excitations of ZnS monolayer honeycomb structure

    Energy Technology Data Exchange (ETDEWEB)

    Shahrokhi, Masoud, E-mail: shahrokhimasoud37@gmail.com

    2016-12-30

    Highlights: • The electronic and optical properties of ZnS honeycomb sheet are investigated. • The electronic properties were analyzed at three levels of GW approach. • The optical properties of these materials are investigated using the BSE approach. • Optical properties of ZnS sheet strongly dominated by excitonic effects. • Spectrum is dominated by strongly bound Frenkel excitons. - Abstract: Using ab-initio density functional theory calculations combined with many-body perturbation formalism we carried out the electronic structure and optical properties of 2D graphene-like ZnS structure. The electronic properties were analyzed at three levels of many-body GW approach (G{sub 0}W{sub 0}, GW{sub 0} and GW) constructed over a Generalized Gradient Approximation functional. Our results indicate that ZnS sheet has a direct band gap at the Γ-point. Also it is seen that inclusion of electron–electron interaction does not change the sort of direct semiconducting band gap in ZnS sheet. The optical properties and excitonic effects of these materials are investigated using the Bethe-Salpeter equation (BSE) approach. The formation of first exciton peaks at 3.86, 4.26, and 4.57 eV with large binding energy of 0.36, 0.49 and 0.73 eV using G{sub 0}W{sub 0} + BSE, GW{sub 0} + BSE and GW + BSE, respectively, was observed. We show that the optical absorption spectrum of 2D ZnS structure is dominated by strongly bound Frenkel excitons. The enhanced excitonic effects in the ZnS monolayer sheet can be useful in designing optoelectronic applications.

  19. Phononic band gap structures as optimal designs

    DEFF Research Database (Denmark)

    Jensen, Jakob Søndergaard; Sigmund, Ole

    2003-01-01

    In this paper we use topology optimization to design phononic band gap structures. We consider 2D structures subjected to periodic loading and obtain the distribution of two materials with high contrast in material properties that gives the minimal vibrational response of the structure. Both in...

  20. Quasiparticle Breakdown in a Quantum Spin Liquid

    International Nuclear Information System (INIS)

    Stone, Matthew B.; Zalinznyak, I.; Hong, T.; Broholm, C.L.; Reich, D.H.

    2006-01-01

    Much of modern condensed matter physics is understood in terms of elementary excitations, or quasiparticles -- fundamental quanta of energy and momentum. Various strongly interacting atomic systems are successfully treated as a collection of quasiparticles with weak or no interactions. However, there are interesting limitations to this description: in some systems the very existence of quasiparticles cannot be taken for granted. Like unstable elementary particles, quasiparticles cannot survive beyond a threshold where certain decay channels become allowed by conservation laws; their spectrum terminates at this threshold. Such quasiparticle breakdown was first predicted for an exotic state of matter -- super-fluid 4 He at temperatures close to absolute zero, a quantum Bose liquid where zero-point atomic motion precludes crystallization. Here we show, using neutron scattering, that quasiparticle breakdown can also occur in a quantum magnet and, by implication, in other systems with Bose quasiparticles. We have measured spin excitations in a two-dimensional quantum magnet, piperazinium hexachlorodicuprate (PHCC), in which spin-1/2 copper ions form a non-magnetic quantum spin liquid, and find remarkable similarities with excitations in superfluid 4 He. We observe a threshold momentum beyond which the quasiparticle peak merges with the two-quasiparticle continuum. It then acquires a finite energy width and becomes indistinguishable from a leading-edge singularity, so that excited states are no longer quasiparticles but occupy a wide band of energy. Our findings have important ramifications for understanding excitations with gapped spectra in many condensed matter systems, ranging from band insulators to high-transition-temperature superconductors.

  1. Exact-exchange-based quasiparticle calculations

    International Nuclear Information System (INIS)

    Aulbur, Wilfried G.; Staedele, Martin; Goerling, Andreas

    2000-01-01

    One-particle wave functions and energies from Kohn-Sham calculations with the exact local Kohn-Sham exchange and the local density approximation (LDA) correlation potential [EXX(c)] are used as input for quasiparticle calculations in the GW approximation (GWA) for eight semiconductors. Quasiparticle corrections to EXX(c) band gaps are small when EXX(c) band gaps are close to experiment. In the case of diamond, quasiparticle calculations are essential to remedy a 0.7 eV underestimate of the experimental band gap within EXX(c). The accuracy of EXX(c)-based GWA calculations for the determination of band gaps is as good as the accuracy of LDA-based GWA calculations. For the lowest valence band width a qualitatively different behavior is observed for medium- and wide-gap materials. The valence band width of medium- (wide-) gap materials is reduced (increased) in EXX(c) compared to the LDA. Quasiparticle corrections lead to a further reduction (increase). As a consequence, EXX(c)-based quasiparticle calculations give valence band widths that are generally 1-2 eV smaller (larger) than experiment for medium- (wide-) gap materials. (c) 2000 The American Physical Society

  2. On the Bengtsson-Frauendorf cranked-quasiparticle model

    International Nuclear Information System (INIS)

    Pal, K.F.; Nagarajan, M.A.; Rowley, N.

    1989-01-01

    The cranked-quasiparticle model of Bengtsson and Frauendorf (non-self-consistent HFB) is compared with some exact calculations of particles moving in a cranked, deformed mean field but interacting via rotationally invariant two-body forces. In order to make the exact calculations manageable, a single shell is used but despite this small basis the quasiparticle model is shown to have a high degree of success. The usual choice of pair gap is discussed and shown to be good. The general structures of band crossings in the exact calculations are well reproduced and some crossing frequencies are given quantitatively though the odd-particle systems require blocking. Interaction strengths are not well reproduced though some qualitative features, e.g. oscillations, are obtained. These interactions are generally underestimated, an effect which causes the HFB yrast band to behave less collectively than it should. (orig.)

  3. Calculating excitons, plasmons, and quasiparticles in 2D materials and van der Waals heterostructures

    DEFF Research Database (Denmark)

    Thygesen, Kristian Sommer

    2017-01-01

    and quasiparticle band structures in 2D materials and their heterostructures. The general theory is illustrated by applications to various types of 2D materials including transition metal dichalcogenides, graphene, phosphorene, and hexagonal boron nitride. The weak and highly non-local dielectric function...

  4. Maximizing band gaps in plate structures

    DEFF Research Database (Denmark)

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

    2006-01-01

    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......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...... theoretically and experimentally and the issue of finite size effects is addressed....

  5. Deformed configurations, band structures and spectroscopic ...

    Indian Academy of Sciences (India)

    2014-03-20

    Mar 20, 2014 ... 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 ...

  6. Microscopic nuclear structure models and methods: chiral symmetry, wobbling motion and γ –bands

    International Nuclear Information System (INIS)

    Sheikh, Javid A; Bhat, Gowhar H; Dar, Waheed A; Jehangir, Sheikh; Ganai, Prince A

    2016-01-01

    A systematic investigation of the nuclear observables related to the triaxial degree of freedom is presented using the multi-quasiparticle triaxial projected shell model (TPSM) approach. These properties correspond to the observation of γ -bands, chiral doublet bands and the wobbling mode. In the TPSM approach, γ -bands are built on each quasiparticle configuration and it is demonstrated that some observations in high-spin spectroscopy that have remained unresolved for quite some time could be explained by considering γ -bands based on two-quasiparticle configurations. It is shown in some Ce-, Nd- and Ge-isotopes that the two observed aligned or s-bands originate from the same intrinsic configuration with one of them as the γ -band based on a two-quasiparticle configuration. In the present work, we have also performed a detailed study of γ -bands observed up to the highest spin in dysposium, hafnium, mercury and uranium isotopes. Furthermore, several measurements related to chiral symmetry breaking and wobbling motion have been reported recently. These phenomena, which are possible only for triaxial nuclei, have been investigated using the TPSM approach. It is shown that doublet bands observed in lighter odd–odd Cs-isotopes can be considered as candidates for chiral symmetry breaking. Transverse wobbling motion recently observed in 135 Pr has also been investigated and it is shown that TPSM approach provides a reasonable description of the measured properties. (invited comment)

  7. Quasiparticle trapping and the quasiparticle multiplier

    International Nuclear Information System (INIS)

    Booth, N.E.

    1987-01-01

    Superconductors and in particular superconducting tunnel junctions can be used to detect phonons, electromagnetic radiation, x rays, and nuclear particles by the mechanism of Cooper-pair breaking to produce excess quasiparticles and phonons. We show that the sensitivity can be increased by a factor of 100 or more by trapping the quasiparticles in another superconductor of lower gap in the region of the tunnel junction. Moreover, if the ratio of the gap energies is >3 a multiplication process can occur due to the interaction of the relaxation phonons. This leads to the concept of the quasiparticle multiplier, a device which could have wider applications than the Gray effect transistor or the quiteron

  8. Zn-VI quasiparticle gaps and optical spectra from many-body calculations.

    Science.gov (United States)

    Riefer, A; Weber, N; Mund, J; Yakovlev, D R; Bayer, M; Schindlmayr, Arno; Meier, C; Schmidt, W G

    2017-06-01

    The electronic band structures of hexagonal ZnO and cubic ZnS, ZnSe, and ZnTe compounds are determined within hybrid-density-functional theory and quasiparticle calculations. It is found that the band-edge energies calculated on the [Formula: see text] (Zn chalcogenides) or GW (ZnO) level of theory agree well with experiment, while fully self-consistent QSGW calculations are required for the correct description of the Zn 3d bands. The quasiparticle band structures are used to calculate the linear response and second-harmonic-generation (SHG) spectra of the Zn-VI compounds. Excitonic effects in the optical absorption are accounted for within the Bethe-Salpeter approach. The calculated spectra are discussed in the context of previous experimental data and present SHG measurements for ZnO.

  9. Wakefield Band Partitioning in LINAC Structures

    International Nuclear Information System (INIS)

    Jones, Roger M

    2003-01-01

    In the NLC project multiple bunches of electrons and positrons will be accelerated initially to a centre of mass of 500 GeV and later to 1 TeV or more. In the process of accelerating 192 bunches within a pulse train, wakefields are excited which kick the trailing bunches off axis and can cause luminosity dilution and BBU (Beam Break Up). Several structures to damp the wakefield have been designed and tested at SLAC and KEK and these have been found to successfully damp the wakefield [1]. However, these 2π/3 structures suffered from electrical breakdown and this has prompted us to explore lower group velocity structures operating at higher fundamental mode phase advances. The wakefield partitioning amongst the bands has been found to change markedly with increased phase advance. Here we report on general trends in the kick factor and associated wakefield band partitioning in dipole bands as a function of phase advance of the synchronous mode in linacs. These results are applicable to both TW (travelling wave) and SW (standing wave) structures

  10. Structure of the Kπ = 4+ bands in 186,188Os

    Science.gov (United States)

    Phillips, A. A.; Garrett, P. E.; Bettermann, L.; Braun, N.; Burke, D. G.; Demand, G. A.; Faestermann, T.; Finlay, P.; Green, K. L.; Hertenberger, R.; Krü; cken, R.; Leach, K. G.; Schumaker, M. A.; Svensson, C. E.; Wirth, H.-F.; Wong, J.

    2009-01-01

    The structures of 3+ states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in 186-192Os as Kπ = 4+ two-phonon vibrations, whereas inelastic scattering, and (t,α) work imply a hexadecapole phonon description. To clarify the nature of these Kπ = 4+ bands in 186,188Os, we performed a (3He,d) reaction on 185,187Re targets using 30 MeV 3He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5° to 50°. Results indicate a significant 5/2+[402]π+3/2+[402]π component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure.

  11. Calculations of quasi-particle spectra of semiconductors under pressure

    DEFF Research Database (Denmark)

    Christensen, Niels Egede; Svane, Axel; Cardona, M.

    2011-01-01

    Different approximations in calculations of electronic quasiparticle states in semiconductors are compared and evaluated with respect to their validity in predictions of optical properties. The quasi-particle self-consistent GW (QSGW) approach yields values of the band gaps which are close...

  12. Quantitative determination of spin-dependent quasiparticle renormalization in ferromagnetic 3d metals

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Barriga, Jaime; Varykhalov, Andrei; Fink, Joerg; Rader, Oliver; Duerr, Hermann; Eberhardt, Wolfgang [Bessy GmbH, Berlin (Germany)

    2008-07-01

    Spin dependent low-energy electronic excitations in 3d ferromagnets are of special interest due to the need of a microscopic understanding of the electronic structure of solids. Low-energy electrons (or holes) become dressed by a cloud of excitations resulting in quasiparticles of a finite lifetime and a different effective mass. These type of excitations have been studied by many theoretical methods, and it has been found that because of many body effects no sharp quasiparticle peaks exist for binding energies larger than 2 eV. Interestingly, it has been shown that strong correlation effects could particularly affect majority spin electrons, leading to a pronounced damping of quasiparticles at binding energies around 2 eV and above. In order to give an experimental corroboration to these findings, we have performed a systematic study of the spin-dependent quasiparticle lifetime and band structure of ferromagnetic 3d transition metal surfaces by means of spin and angle-resolved photoemission spectroscopy. On hcp Co(0001), fcc Ni(111) and bcc Fe(110), we have found a more pronounced renormalization of the majority spin quasiparticle spectral weight going from Ni to Co which are both strong ferromagnets. For Fe, a weak ferromagnet, such a process becomes more prominent in the minority channel.

  13. Surface band structures on Nb(001)

    International Nuclear Information System (INIS)

    Fang, B.; Lo, W.; Chien, T.; Leung, T.C.; Lue, C.Y.; Chan, C.T.; Ho, K.M.

    1994-01-01

    We report the joint studies of experimental and theoretical surface band structures of Nb(001). Angle-resolved photoelectron spectroscopy was used to determine surface-state dispersions along three high-symmetry axes bar Γ bar M, bar Γ bar X, and bar M bar X in the surface Brillouin zone. Ten surface bands have been identified. The experimental data are compared to self-consistent pseudopotential calculations for the 11-layer Nb(001) slabs that are either bulk terminated or fully relaxed (with a 12% contraction for the first interlayer spacing). The band calculations for a 12% surface-contracted slab are in better agreement with the experimental results than those for a bulk-terminated slab, except for a surface resonance near the Fermi level, which is related to the spin-orbit interaction. The charge profiles for all surface states or resonances have been calculated. Surface contraction effects on the charge-density distribution and the energy position of surface states and resonances will also be discussed

  14. Changing optical band structure with single photons

    Science.gov (United States)

    Albrecht, Andreas; Caneva, Tommaso; Chang, Darrick E.

    2017-11-01

    Achieving strong interactions between individual photons enables a wide variety of exciting possibilities in quantum information science and many-body physics. Cold atoms interfaced with nanophotonic structures have emerged as a platform to realize novel forms of nonlinear interactions. In particular, when atoms are coupled to a photonic crystal waveguide, long-range atomic interactions can arise that are mediated by localized atom-photon bound states. We theoretically show that in such a system, the absorption of a single photon can change the band structure for a subsequent photon. This occurs because the first photon affects the atoms in the chain in an alternating fashion, thus leading to an effective period doubling of the system and a new optical band structure for the composite atom-nanophotonic system. We demonstrate how this mechanism can be engineered to realize a single-photon switch, where the first incoming photon switches the system from being highly transmissive to highly reflective, and analyze how signatures can be observed via non-classical correlations of the outgoing photon field.

  15. Ab initio quasiparticle bandstructure of ABA and ABC-stacked graphene trilayers

    Science.gov (United States)

    Menezes, Marcos; Capaz, Rodrigo; Louie, Steven

    2013-03-01

    We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW π bands to a low energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the quasiparticle corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher energy bands, which is proportional to the nearest neighbor interlayer hopping parameter γ1. Both features are brought to closer agreement with experiment through the quasiparticle corrections. Finally, other effects, such as trigonal warping, electron-hole assymetry and energy gaps are discussed in terms of the associated parameters. This work was supported by the Brazilian funding agencies: CAPES, CNPq, FAPERJ and INCT-Nanomateriais de Carbono. It was also supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231.

  16. Band structure dynamics in indium wires

    Science.gov (United States)

    Chávez-Cervantes, M.; Krause, R.; Aeschlimann, S.; Gierz, I.

    2018-05-01

    One-dimensional indium wires grown on Si(111) substrates, which are metallic at high temperatures, become insulating below ˜100 K due to the formation of a charge density wave (CDW). The physics of this transition is not conventional and involves a multiband Peierls instability with strong interband coupling. This CDW ground state is readily destroyed with femtosecond laser pulses resulting in a light-induced insulator-to-metal phase transition. The current understanding of this transition remains incomplete, requiring measurements of the transient electronic structure to complement previous investigations of the lattice dynamics. Time- and angle-resolved photoemission spectroscopy with extreme ultraviolet radiation is applied to this end. We find that the transition from the insulating to the metallic band structure occurs within ˜660 fs, which is a fraction of the amplitude mode period. The long lifetime of the transient state (>100 ps) is attributed to trapping in a metastable state in accordance with previous work.

  17. Quasiparticle method in relativistic mean-field theories of nuclear structure

    International Nuclear Information System (INIS)

    Ai, H.

    1988-01-01

    In recent years, in order to understand the success of Dirac phenomenology, relativistic Brueckner-Hartree-Fock (RBHF) theory has been developed. This theory is a relativistic many-body theory of nuclear structure. Based upon the RBHF theory, which is characterized as having no free parameters other than those introduced in fitting free-space nucleon-nucleon scattering data, we construct an effective interaction. This interaction, when treated in a relativistic Hartree-Fock approximation, reproduces, rather accurately, the nucleon self-energy in nuclear matter, Migdal parameters obtained via relativistic Brueckner-Hartree-Fock calculations, and the saturation curves calculated with the full relativistic Brueckner-Hartree-Fock theory. This effective interaction is constructed by adding a number of pseudoparticles to the mesons used to construct one-boson-exchange (OBE) models of the nuclear force. The pseudoparticles have relatively large masses and either real or imaginary coupling constants. (For example, exchange of a pseudo-sigma with an imaginary coupling constant has the effect of reducing the scalar attraction arising from sigma exchange, while exchange of a pseudo-omega with an imaginary coupling constant has the effect of reducing the repulsion arising from omega exchange. The terms beyond the Born term in the case of pion exchange are well simulated by pseudo-sigma exchange with a real coupling constant.) The effective interaction constructed here may be used for calculations of the properties of finite nuclei in a relativistic Hartree-Fock approximation

  18. Interband quasiparticle scattering in superconducting LiFeAs reconciles photoemission and tunneling measurements.

    Science.gov (United States)

    Hess, Christian; Sykora, Steffen; Hänke, Torben; Schlegel, Ronny; Baumann, Danny; Zabolotnyy, Volodymyr B; Harnagea, Luminita; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd

    2013-01-04

    Several angle-resolved photoemission spectroscopy (ARPES) studies reveal a poorly nested Fermi surface of LiFeAs, far away from a spin density wave instability, and clear-cut superconducting gap anisotropies. On the other hand a very different, more nested Fermi surface and dissimilar gap anisotropies have been obtained from quasiparticle interference (QPI) data, which were interpreted as arising from intraband scattering within holelike bands. Here we show that this ARPES-QPI paradox is completely resolved by interband scattering between the holelike bands. The resolution follows from an excellent agreement between experimental quasiparticle scattering data and T-matrix QPI calculations (based on experimental band structure data), which allows disentangling interband and intraband scattering processes.

  19. Electronic Band Structure of Helical Polyisocyanides.

    Science.gov (United States)

    Champagne, Benoît; Liégeois, Vincent; Fripiat, Joseph G; Harris, Frank E

    2017-10-19

    Restricted Hartree-Fock computations are reported for a methyl isocyanide polymer (repeating unit -C═N-CH 3 ), whose most stable conformation is expected to be a helical chain. The computations used a standard contracted Gaussian orbital set at the computational levels STO-3G, 3-21G, 6-31G, and 6-31G**, and studies were made for two line-group configurations motivated by earlier work and by studies of space-filling molecular models: (1) A structure of line-group symmetry L9 5 , containing a 9-fold screw axis with atoms displaced in the axial direction by 5/9 times the lattice constant, and (2) a structure of symmetry L4 1 that had been proposed, containing a 4-fold screw axis with translation by 1/4 of the lattice constant. Full use of the line-group symmetry was employed to cause most of the computational complexity to depend only on the size of the asymmetric repeating unit. Data reported include computed bond properties, atomic charge distribution, longitudinal polarizability, band structure, and the convoluted density of states. Most features of the description were found to be insensitive to the level of computational approximation. The work also illustrates the importance of exploiting line-group symmetry to extend the range of polymer structural problems that can be treated computationally.

  20. Dipole Bands in 196Hg

    International Nuclear Information System (INIS)

    Lawrie, J. J.; Lawrie, E. A.; Newman, R. T.; Sharpey-Schafer, J. F.; Smit, F. D.; Msezane, B.; Benatar, M.; Mabala, G. K.; Mutshena, K. P.; Federke, M.; Mullins, S. M.; Ncapayi, N. J.; Vymers, P.

    2011-01-01

    High spin states in 196 Hg have been populated in the 198 Pt(α,6n) reaction at 65 MeV and the level scheme has been extended. A new dipole band has been observed and a previously observed dipole has been confirmed. Excitation energies, spins and parities of these bands were determined from DCO ratio and linear polarization measurements. Possible quasiparticle excitations responsible for these structures are discussed.

  1. Electronic band structures of binary skutterudites

    International Nuclear Information System (INIS)

    Khan, Banaras; Aliabad, H.A. Rahnamaye; Saifullah; Jalali-Asadabadi, S.; Khan, Imad; Ahmad, Iftikhar

    2015-01-01

    The electronic properties of complex binary skutterudites, MX 3 (M = Co, Rh, Ir; X = P, As, Sb) are explored, using various density functional theory (DFT) based theoretical approaches including Green's Function (GW) as well as regular and non-regular Tran Blaha modified Becke Jhonson (TB-mBJ) methods. The wide range of calculated bandgap values for each compound of this skutterudites family confirm that they are theoretically as challenging as their experimental studies. The computationally expensive GW method, which is generally assume to be efficient in the reproduction of the experimental bandgaps, is also not very successful in the calculation of bandgaps. In this article, the issue of the theoretical bandgaps of these compounds is resolved by reproducing the accurate experimental bandgaps, using the recently developed non-regular TB-mBJ approach, based on DFT. The effectiveness of this technique is due to the fact that a large volume of the binary skutterudite crystal is empty and hence quite large proportion of electrons lie outside of the atomic spheres, where unlike LDA and GGA which are poor in the treatment of these electrons, this technique properly treats these electrons and hence reproduces the clear electronic picture of these compounds. - Highlights: • Theoretical and experimental electronic band structures of binary skutterudites are reviewed. • The literature reveals that none of the existing theoretical results are consistent with the experiments. • GW, regular and non-regular TB-mBJ methods are used to reproduce the correct results. • The GW and regular TB-mBJ results are better than the available results in literature. • However, non-regular TB-mBJ reproduces the correct experimental band structures

  2. Electronic band structures of binary skutterudites

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Banaras [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Aliabad, H.A. Rahnamaye [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Saifullah [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Jalali-Asadabadi, S. [Department of Physics, Faculty of Science, University of Isfahan (UI), 81744 Isfahan (Iran, Islamic Republic of); Khan, Imad [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Ahmad, Iftikhar, E-mail: ahma5532@gmail.com [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan)

    2015-10-25

    The electronic properties of complex binary skutterudites, MX{sub 3} (M = Co, Rh, Ir; X = P, As, Sb) are explored, using various density functional theory (DFT) based theoretical approaches including Green's Function (GW) as well as regular and non-regular Tran Blaha modified Becke Jhonson (TB-mBJ) methods. The wide range of calculated bandgap values for each compound of this skutterudites family confirm that they are theoretically as challenging as their experimental studies. The computationally expensive GW method, which is generally assume to be efficient in the reproduction of the experimental bandgaps, is also not very successful in the calculation of bandgaps. In this article, the issue of the theoretical bandgaps of these compounds is resolved by reproducing the accurate experimental bandgaps, using the recently developed non-regular TB-mBJ approach, based on DFT. The effectiveness of this technique is due to the fact that a large volume of the binary skutterudite crystal is empty and hence quite large proportion of electrons lie outside of the atomic spheres, where unlike LDA and GGA which are poor in the treatment of these electrons, this technique properly treats these electrons and hence reproduces the clear electronic picture of these compounds. - Highlights: • Theoretical and experimental electronic band structures of binary skutterudites are reviewed. • The literature reveals that none of the existing theoretical results are consistent with the experiments. • GW, regular and non-regular TB-mBJ methods are used to reproduce the correct results. • The GW and regular TB-mBJ results are better than the available results in literature. • However, non-regular TB-mBJ reproduces the correct experimental band structures.

  3. Temperature dependent quasiparticle renormalization in nickel and iron

    Energy Technology Data Exchange (ETDEWEB)

    Ovsyannikov, Ruslan; Thirupathaiah, Setti; Sanchez-Barriga, Jaime; Fink, Joerg; Duerr, Hermann [Helmholtz Zentrum Berlin, BESSY II, Albert-Einstein-Strasse 15, D-12489 Berlin (Germany)

    2010-07-01

    One of the fundamental consequences of electron correlation effects is that the bare particles in solids become 'dressed' with an excitation cloud resulting in quasiparticles. Such a quasiparticle will carry the same spin and charge as the original particle, but will have a renormalized mass and a finite lifetime. The properties of many-body interactions are described with a complex function called self energy which is directly accessible to modern high-resolution angle resolved photoemission spectroscopy (ARPES). Ferromagnetic metals like nickel or iron offers the exciting possibility to study the spin dependence of quasiparticle coupling to bosonic modes. Utilizing the exchange split band structure as an intrinsic 'spin detector' it is possible to distinguish between electron-phonon and electron-magnon coupling phenomena. In this contribution we will report a systematic investigation of the k- and temperature dependence of the electron-boson coupling in nickel and iron metals as well as discuss origin of earlier observed anomalous lifetime broadening of majority spin states of nickel at Fermi level.

  4. Quasiparticles in condensed matter systems

    Science.gov (United States)

    Wölfle, Peter

    2018-03-01

    Quasiparticles are a powerful concept of condensed matter quantum theory. In this review, the appearence and the properties of quasiparticles are presented in a unifying perspective. The principles behind the existence of quasiparticle excitations in both quantum disordered and ordered phases of fermionic and bosonic systems are discussed. The lifetime of quasiparticles is considered in particular near a continuous classical or quantum phase transition, when the nature of quasiparticles on both sides of a transition into an ordered state changes. A new concept of critical quasiparticles near a quantum critical point is introduced, and applied to quantum phase transitions in heavy fermion metals. Fractional quasiparticles in systems of restricted dimensionality are reviewed. Dirac quasiparticles emerging in so-called Dirac materials are discussed. The more recent discoveries of topologically protected chiral quasiparticles in topological matter and Majorana quasiparticles in topological superconductors are briefly reviewed.

  5. Band structures in fractal grading porous phononic crystals

    Science.gov (United States)

    Wang, Kai; Liu, Ying; Liang, Tianshu; Wang, Bin

    2018-05-01

    In this paper, a new grading porous structure is introduced based on a Sierpinski triangle routine, and wave propagation in this fractal grading porous phononic crystal is investigated. The influences of fractal hierarchy and porosity on the band structures in fractal graidng porous phononic crystals are clarified. Vibration modes of unit cell at absolute band gap edges are given to manifest formation mechanism of absolute band gaps. The results show that absolute band gaps are easy to form in fractal structures comparatively to the normal ones with the same porosity. Structures with higher fractal hierarchies benefit multiple wider absolute band gaps. This work provides useful guidance in design of fractal porous phononic crystals.

  6. Quasi-particle interference of heavy fermions in resonant x-ray scattering.

    Science.gov (United States)

    Gyenis, András; da Silva Neto, Eduardo H; Sutarto, Ronny; Schierle, Enrico; He, Feizhou; Weschke, Eugen; Kavai, Mariam; Baumbach, Ryan E; Thompson, Joe D; Bauer, Eric D; Fisk, Zachary; Damascelli, Andrea; Yazdani, Ali; Aynajian, Pegor

    2016-10-01

    Resonant x-ray scattering (RXS) has recently become an increasingly important tool for the study of ordering phenomena in correlated electron systems. Yet, the interpretation of RXS experiments remains theoretically challenging because of the complexity of the RXS cross section. Central to this debate is the recent proposal that impurity-induced Friedel oscillations, akin to quasi-particle interference signals observed with a scanning tunneling microscope (STM), can lead to scattering peaks in RXS experiments. The possibility that quasi-particle properties can be probed in RXS measurements opens up a new avenue to study the bulk band structure of materials with the orbital and element selectivity provided by RXS. We test these ideas by combining RXS and STM measurements of the heavy fermion compound Ce M In 5 ( M = Co, Rh). Temperature- and doping-dependent RXS measurements at the Ce- M 4 edge show a broad scattering enhancement that correlates with the appearance of heavy f -electron bands in these compounds. The scattering enhancement is consistent with the measured quasi-particle interference signal in the STM measurements, indicating that the quasi-particle interference can be probed through the momentum distribution of RXS signals. Overall, our experiments demonstrate new opportunities for studies of correlated electronic systems using the RXS technique.

  7. Decay spectroscopy of 160Sm: The lightest four-quasiparticle K isomer

    Directory of Open Access Journals (Sweden)

    Z. Patel

    2016-02-01

    Full Text Available The decay of a new four-quasiparticle isomeric state in 160Sm has been observed using γ-ray spectroscopy at the RIBF, RIKEN. The four-quasiparticle state is assigned a 2π⊗2ν π52−[532], π52+[413], ν52−[523], ν72+[633] configuration. The half-life of this (11+ state is measured to be 1.8(4 μs. The (11+ isomer decays into a rotational band structure, based on a (6− ν52−[523]⊗ν72+[633] bandhead, consistent with the gK−gR values. This decays to a (5− two-proton quasiparticle state, which in turn decays to the ground state band. Potential energy surface and blocked-BCS calculations were performed in the deformed midshell region around 160Sm. They reveal a significant influence from β6 deformation and that 160Sm is the best candidate for the lightest four-quasiparticle K isomer to exist in this region. The relationship between reduced hindrance and isomer excitation energy for E1 transitions from multiquasiparticle states is considered with the new data from 160Sm. The E1 data are found to agree with the existing relationship for E2 transitions.

  8. Quasiparticle dynamics in reshaped helical Dirac cone of topological insulators.

    Science.gov (United States)

    Miao, Lin; Wang, Z F; Ming, Wenmei; Yao, Meng-Yu; Wang, Meixiao; Yang, Fang; Song, Y R; Zhu, Fengfeng; Fedorov, Alexei V; Sun, Z; Gao, C L; Liu, Canhua; Xue, Qi-Kun; Liu, Chao-Xing; Liu, Feng; Qian, Dong; Jia, Jin-Feng

    2013-02-19

    Topological insulators and graphene present two unique classes of materials, which are characterized by spin-polarized (helical) and nonpolarized Dirac cone band structures, respectively. The importance of many-body interactions that renormalize the linear bands near Dirac point in graphene has been well recognized and attracted much recent attention. However, renormalization of the helical Dirac point has not been observed in topological insulators. Here, we report the experimental observation of the renormalized quasiparticle spectrum with a skewed Dirac cone in a single Bi bilayer grown on Bi(2)Te(3) substrate from angle-resolved photoemission spectroscopy. First-principles band calculations indicate that the quasiparticle spectra are likely associated with the hybridization between the extrinsic substrate-induced Dirac states of Bi bilayer and the intrinsic surface Dirac states of Bi(2)Te(3) film at close energy proximity. Without such hybridization, only single-particle Dirac spectra are observed in a single Bi bilayer grown on Bi(2)Se(3), where the extrinsic Dirac states Bi bilayer and the intrinsic Dirac states of Bi(2)Se(3) are well separated in energy. The possible origins of many-body interactions are discussed. Our findings provide a means to manipulate topological surface states.

  9. Multiple band structure in 156Er

    International Nuclear Information System (INIS)

    Sunyar, A.W.; Der Mateosian, E.; Kistner, O.C.; Johnson, A.; Lumpkin, A.H.; Thieberger, P.

    1976-01-01

    The 142 Nd( 18 O,4n) 156 Er reaction at 90-95 MeV was used to study 156 Er high-spin states to spin 24. In addition to the background ground-state band, two well developed off-spin side bands, one of each parity, were observed. (Auth.)

  10. Gamma bands in doubly odd rhenium and iridium nuclei

    Directory of Open Access Journals (Sweden)

    Balodis M.

    2015-01-01

    Full Text Available Structure of the |K ± 2| bands in doubly-odd nuclei belonging to the transitional deformation region at A∼190 is discussed. Relation of these quasi gamma-bands with the non-axial deformation of the parent two-quasiparticle configurations is studied. Using available experimental information, new tentative |K ± 2| bands are proposed in 188Re, and 192,194Ir nuclei. Coexistence of two-quasiparticle states with different deformation modes is considered in the case of 188Re and 194Ir.

  11. Band structure studies of actinide systems

    International Nuclear Information System (INIS)

    Koelling, D.D.

    1976-01-01

    The nature of the f-orbitals in an actinide system plays a crucial role in determining the electronic properties. It has long been realized that when the actinide separation is small enough for the f-orbitals to interact directly, the system will exhibit itinerant electron properties: an absence of local moment due to the f-orbitals and sometimes even superconductivity. However, a number of systems with the larger actinide separation that should imply local moment behavior also exhibit intinerant properties. Such systems (URh 3 , UIr 3 , UGe 3 , UC) were examined to learn something about the other f-interactions. A preliminary observation made is that there is apparently a very large and ansiotropic mass enhancement in these systems. There is very good reason to believe that this is not solely due to large electron--electron correlations but to a large electron--phonon interaction as well. These features of the ''non-magnetic'', large actinide separation systems are discussed in light of our results to date. Finally, the results of some recent molecular calculations on actinide hexafluorides are used to illustrate the shielding effects on the intra-atomic Coulomb term U/sub f-f/ which would appear in any attempt to study the formation of local moments. As one becomes interested in materials for which a band structure is no longer an adequate model, this screened U/sub ff/ is the significant parameter and efforts must be made to evaluate it in solid state systems

  12. Quasiparticle--phonon model of the nucleus. V. Odd spherical nuclei

    International Nuclear Information System (INIS)

    Vdovin, A.I.; Voronov, V.V.; Solov'ev, V.G.; Stoyanov, C.

    1985-01-01

    The formalism of the quasiparticle--phonon model of the nucleus for odd spherical nuclei is presented. The exact commutation relations of the quasiparticle and phonon operators together with the anharmonic corrections for the phonon excitations are taken into account in the derivation of equations for the energies and structure coefficients of the wave functions of excited states, which include quasiparticle--phonon and quasiparticle--two-phonon components. The influence of various physical effects and of the dimension of the phonon basis on the fragmentation of the single-quasiparticle and quasiparticle-phonon states is investigated

  13. Quasiparticles and Fermi liquid behaviour in an organic metal

    Science.gov (United States)

    Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.

    2012-01-01

    Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143

  14. Band Structure Characteristics of Nacreous Composite Materials with Various Defects

    Science.gov (United States)

    Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.

    2016-06-01

    Nacreous composite materials have excellent mechanical properties, such as high strength, high toughness, and wide phononic band gap. In order to research band structure characteristics of nacreous composite materials with various defects, supercell models with the Brick-and-Mortar microstructure are considered. An efficient multi-level substructure algorithm is employed to discuss the band structure. Furthermore, two common systems with point and line defects and varied material parameters are discussed. In addition, band structures concerning straight and deflected crack defects are calculated by changing the shear modulus of the mortar. Finally, the sensitivity of band structures to the random material distribution is presented by considering different volume ratios of the brick. The results reveal that the first band gap of a nacreous composite material is insensitive to defects under certain conditions. It will be of great value to the design and synthesis of new nacreous composite materials for better dynamic properties.

  15. Quasiparticle electronic and optical properties of the Si-Sn system

    International Nuclear Information System (INIS)

    Jensen, Rasmus V S; Pedersen, Thomas G; Larsen, Arne N

    2011-01-01

    The Si 1-x Sn x material system is an interesting candidate for an optically active material compatible with Si. Based on density functional theory with quasiparticle corrections we calculate the electronic band structure of zinc-blende SiSn under both compressive and tensile strain. At 2.2% tensile strain the band gap becomes direct with a magnitude of 0.85 eV. We develop an accurate tight-binding parameterization of the electronic structure and calculate the optical properties of SiSn. Furthermore, the silicide SiSn 2 is investigated and found to have metallic character. (paper)

  16. The Marvels of Electromagnetic Band Gap (EBG) Structures

    Science.gov (United States)

    2003-11-01

    terminology of "Electromagnetic conference papers and journal articles dealing with Band- gaps (EBG)". Recently, many researchers the characterizations...Band Gap (EBG) Structures 9 utilized to reduce the mutual coupling between Structures: An FDTD/Prony Technique elements of antenna arrays. based on the...Band- Gap of several patents. He has had pioneering research contributions in diverse areas of electromagnetics,Snteructure", Dymposiget o l 21 IE 48

  17. Superconductors with excess quasiparticles

    International Nuclear Information System (INIS)

    Elesin, V.F.; Kopaev, Y.V.

    1981-01-01

    This review presents a systematic kinetic theory of nonequilibrium phenomena in superconductors with excess quasiparticles created by electromagnetic or tunnel injection. The energy distributions of excess quasiparticles and of nonequilibrium phonons, dependence of the order parameter on the power and frequency (or intensity) of the electromagnetic field, magnetic properties of nonequilibrium superconductors, I-V curves of superconductor-insulator-superconductor junctions, and other properties are described in detail. The stability of superconducting states far from thermodynamic equilibrium is investigated and it is shown that characteristic instabilities leading to the formation of nonuniform states of a new type or phase transitions of the first kind are inherent to superconductors with excess quasiparticles. The results are compared with experimental data

  18. Amniotic band-like structures | Govender | Obstetrics and ...

    African Journals Online (AJOL)

    Intra-amniotic band-like structures are seen fairly commonly on routine obstetric scans, especially during the first and second trimesters of pregnancy. It is important to establish the cause for such findings in order to determine their clinical significance and to assess prognosis. The vast majority of band-like structures are ...

  19. Structure of dipole bands in 106In

    International Nuclear Information System (INIS)

    Deo, A. Y.; Palit, R.; Naik, Z.; Joshi, P. K.; Mazumdar, I.; Sihotra, S.; Mehta, D.; Kumar, S.; Chakrabarti, R.; Kshetri, R.; Jain, H. C.

    2009-01-01

    High spin states in neutron-deficient 106 In were investigated using 78 Se( 32 S,p3n) reaction at 125 MeV. The level scheme is extended up to 7 MeV of excitation energy for the negative parity states constituting four dipole bands, and the positive parity states which mainly exhibit single-particle excitations are extended up to 5 MeV. Projected deformed Hartree-Fock calculations were carried out to understand the configurations of different bands in this nucleus.

  20. Effect of electronic correlations on the quasiparticle dispersion of USb2

    International Nuclear Information System (INIS)

    Yang Xiaodong; Riseborough, Peter S; Durakiewicz, Tomasz; Oppeneer, P M; Elgazzar, S

    2010-01-01

    Angle resolved photoemission experiments have been performed on USb 2 , and very narrow quasiparticle peaks have been observed in a band which LSDA predicts to osculate the Fermi-energy. The observed band is found to be depressed by 17 meV below the Fermi-energy, furthermore, the inferred quasiparticle dispersion relation for this band exhibits a kink at an energy of about 23 meV below the Fermi-energy. The kink is not found in LSDA calculations and, therefore, is attributable to a change in the quasiparticle mass renormalization by a factor of approximately 2. The existence of a kink in the quasiparticle dispersion relation of a band which does not cross the Fermi-energy is unprecedented. The origin of the observed depression of the band, its quasi-particle mass enhancement, and the characteristic energy are discussed on the basis of a theoretical model.

  1. Quasiparticle-phonon coupling in inelastic proton scattering

    International Nuclear Information System (INIS)

    Weissbach, B.

    1980-01-01

    Multistep-processes in inelastic proton scattering from 89 Y are analyzed by using CCBA and DWBA on a quasiparticle phonon nuclear structure model. Indirect excitations caused by quasiparticle phonon coupling effects are found to be very important for the transition strengths and the shape of angular distributions. Core excitations are dominant for the higher order steps of the reaction. (author)

  2. The complex band structure for armchair graphene nanoribbons

    International Nuclear Information System (INIS)

    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 nanoribbons, and is also classified into three classes

  3. Band structures in the nematic elastomers phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Shuai [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China); School of Civil Engineering and Architecture, Anyang Normal University, Anyang 455000 (China); Liu, Ying, E-mail: yliu5@bjtu.edu.cn [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China); Liang, Tianshu [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China)

    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.

  4. Band structures in the nematic elastomers phononic crystals

    International Nuclear Information System (INIS)

    Yang, Shuai; Liu, Ying; Liang, Tianshu

    2017-01-01

    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. Electronic band structure of lithium, sodium and potassium fluorides

    International Nuclear Information System (INIS)

    Jouanin, C.; Albert, J.P.; Gout, C.

    1975-01-01

    A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good

  6. A systematic study of band structure and electromagnetic properties of neutron rich odd mass Eu isotopes in the projected shell model framework

    Energy Technology Data Exchange (ETDEWEB)

    Pandit, Rakesh K.; Devi, Rani [University of Jammu, Department of Physics and Electronics, Jammu (India); Khosa, S.K. [Central University of Jammu, Department of Physics and Astronomical Sciences, Jammu (India); Bhat, G.H.; Sheikh, J.A. [University of Kashmir, Department of Physics, Srinagar (India)

    2017-10-15

    The positive and negative parity rotational band structure of the neutron rich odd mass Eu isotopes with neutron numbers ranging from 90 to 96 are investigated up to the high angular momentum. In the theoretical analysis of energy spectra, transition energies and electromagnetic transition probabilities we employ the projected shell model. The calculations successfully describe the formation of the ground and excited band structures from the single particle and multi quasiparticle configurations. Calculated excitation energy spectra, transition energies, exact quantum mechanically calculated B(E2) and B(M1) transition probabilities are compared with experimental data wherever available and a reasonably good agreement is obtained with the observed data. The change in deformation in the ground state band with the increase in angular momentum and the increase in neutron number has also been established. (orig.)

  7. Quasi-particle and collective magnetism: Rotation, pairing and blocking in high-K isomers

    International Nuclear Information System (INIS)

    Stone, N.J.; Stone, J.R.; Walker, P.M.; Bingham, C.R.

    2013-01-01

    For the first time, a wide range of collective magnetic g-factors g R , obtained from a novel analysis of experimental data for multi-quasi-particle configurations in high-K isomers, is shown to exhibit a striking systematic variation with the relative number of proton and neutron quasi-particles, N p −N n . Using the principle of additivity, the quasi-particle contribution to magnetism in high-K isomers of Lu–Re, Z=71–75, has been estimated. Based on these estimates, band-structure branching ratio data are used to explore the behavior of the collective contribution as the number and proton/neutron nature (N p , N n ), of the quasi-particle excitations, change. Basic ideas of pairing, its quenching by quasi-particle excitation and the consequent changes to moment of inertia and collective magnetism are discussed. Existing model calculations do not reproduce the observed g R variation adequately. The paired superfluid system of nucleons in these nuclei, and their excitations, present properties of general physics interest. The new-found systematic behavior of g R in multi-quasi-particle excitations of this unique system, showing variation from close to zero for multi-neutron states to above 0.5 for multi-proton states, opens a fresh window on these effects and raises the important question of just which nucleons contribute to the ‘collective’ properties of these nuclei

  8. Band structures in Sierpinski triangle fractal porous phononic crystals

    International Nuclear Information System (INIS)

    Wang, Kai; Liu, Ying; Liang, Tianshu

    2016-01-01

    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.

  9. 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.

  10. Quasiparticles and thermodynamical consistency

    International Nuclear Information System (INIS)

    Shanenko, A.A.; Biro, T.S.; Toneev, V.D.

    2003-01-01

    A brief and simple introduction into the problem of the thermodynamical consistency is given. The thermodynamical consistency relations, which should be taken into account under constructing a quasiparticle model, are found in a general manner from the finite-temperature extension of the Hellmann-Feynman theorem. Restrictions following from these relations are illustrated by simple physical examples. (author)

  11. Long-range spin-singlet proximity effect for a Josephson system with a single-crystal ferromagnet due to its band-structure features

    Science.gov (United States)

    Avdeev, M. V.; Proshin, Yu. N.

    2018-03-01

    A possible explanation for the long-range proximity effect observed in single-crystalline cobalt nanowires sandwiched between two tungsten superconducting electrodes [Nat. Phys. 6, 389 (2010), 10.1038/nphys1621] is proposed. The theoretical model uses properties of a ferromagnet band structure. Specifically, to connect the exchange field with the momentum of quasiparticles the distinction between the effective masses in majority and minority spin subbands and the Fermi-surface anisotropy are considered. The derived Eilenberger-like equations allowed us to obtain a renormalized exchange interaction that is completely compensated for some crystallographic directions under certain conditions. The proposed theoretical model is compared with previous approaches.

  12. Analysis on X-band structure breakdown at GLCTA

    International Nuclear Information System (INIS)

    Suehara, T.; Sanuki, T.; Komamiya, S.; Higo, T.; Hayano, H.; Terunuma, N.; Saeki, T.; Watanabe, K.; Hayakawa, A.; Tsukada, Y.

    2004-01-01

    We have built a new monitoring system for accelerator structure breakdown in the X-band high-gradient test facility at KEK (GLCTA: Global Linear Collider Test Accelerator). An X-band test structure KX01 (made by KEK) has been processed at GLCTA and we have been collecting data for about 3 months using this breakdown monitoring system. We describe overview of the monitoring system and preliminary result of breakdown analysis of the structure. (author)

  13. Shell model description of band structure in 48Cr

    International Nuclear Information System (INIS)

    Vargas, Carlos E.; Velazquez, Victor M.

    2007-01-01

    The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements

  14. Band structure of superlattice with δ-like potential

    International Nuclear Information System (INIS)

    Gashimzade, N.F.; Gashimzade, F.M.; Hajiev, A.T.

    1993-08-01

    Band structure of superlattice with δ-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

  15. Band connectivity for topological quantum chemistry: Band structures as a graph theory problem

    Science.gov (United States)

    Bradlyn, Barry; Elcoro, L.; Vergniory, M. G.; Cano, Jennifer; Wang, Zhijun; Felser, C.; Aroyo, M. I.; Bernevig, B. Andrei

    2018-01-01

    The conventional theory of solids is well suited to describing band structures locally near isolated points in momentum space, but struggles to capture the full, global picture necessary for understanding topological phenomena. In part of a recent paper [B. Bradlyn et al., Nature (London) 547, 298 (2017), 10.1038/nature23268], we have introduced the way to overcome this difficulty by formulating the problem of sewing together many disconnected local k .p band structures across the Brillouin zone in terms of graph theory. In this paper, we give the details of our full theoretical construction. We show that crystal symmetries strongly constrain the allowed connectivities of energy bands, and we employ graph theoretic techniques such as graph connectivity to enumerate all the solutions to these constraints. The tools of graph theory allow us to identify disconnected groups of bands in these solutions, and so identify topologically distinct insulating phases.

  16. Transport in bilayer and trilayer graphene: band gap engineering and band structure tuning

    Science.gov (United States)

    Zhu, Jun

    2014-03-01

    Controlling the stacking order of atomically thin 2D materials offers a powerful tool to control their properties. Linearly dispersed bands become hyperbolic in Bernal (AB) stacked bilayer graphene (BLG). Both Bernal (ABA) and rhombohedral (ABC) stacking occur in trilayer graphene (TLG), producing distinct band structures and electronic properties. A symmetry-breaking electric field perpendicular to the sample plane can further modify the band structures of BLG and TLG. In this talk, I will describe our experimental effort in these directions using dual-gated devices. Using thin HfO2 film deposited by ALD as gate dielectric, we are able to apply large displacement fields D > 6 V/nm and observe the opening and saturation of the field-induced band gap Eg in bilayer and ABC-stacked trilayer graphene, where the conduction in the mid gap changes by more than six decades. Its field and temperature dependence highlights the crucial role played by Coulomb disorder in facilitating hopping conduction and suppressing the effect of Eg in the tens of meV regime. In contrast, mid-gap conduction decreases with increasing D much more rapidly in clean h-BN dual-gated devices. Our studies also show the evolution of the band structure in ABA-stacked TLG, in particular the splitting of the Dirac-like bands in large D field and the signatures of two-band transport at high carrier densities. Comparison to theory reveals the need for more sophisticated treatment of electronic screening beyond self-consistent Hartree calculations to accurately predict the band structures of trilayer graphene and graphenic materials in general.

  17. Enhancement of phononic band gaps in ternary/binary structure

    International Nuclear Information System (INIS)

    Aly, Arafa H.; Mehaney, Ahmed

    2012-01-01

    Based on the transfer matrix method (TMM) and Bloch theory, the interaction of elastic waves (normal incidence) with 1D phononic crystal had been studied. The transfer matrix method was obtained for both longitudinal and transverse waves by applying the continuity conditions between the consecutive unit cells. Dispersion relations are calculated and plotted for both binary and ternary structures. Also we have investigated the corresponding effects on the band gaps values for the two types of phononic crystals. Furthermore, it can be observed that the complete band gaps are located in the common frequency stop-band regions. Numerical simulations are performed to investigate the effect of different thickness ratios inside each unit cell on the band gap values, as well as unit cells thickness on the central band gap frequency. These phononic band gap materials can be used as a filter for elastic waves at different frequencies values.

  18. Two-dimensional microwave band-gap structures of different ...

    Indian Academy of Sciences (India)

    - stant and/or magnetic permeability (or in particular impedance) are periodic and the propagation of electromagnetic waves is forbidden at certain frequencies when allowed to pass through these structures. This is similar to the electronic band.

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

    International Nuclear Information System (INIS)

    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

  20. Band-Structure of Thallium by the LMTO Method

    DEFF Research Database (Denmark)

    Holtham, P. M.; Jan, J. P.; Skriver, Hans Lomholt

    1977-01-01

    by an energy gap. The 6d and 7s bands were found to be far above the Fermi level and the 5d states were found to be far below it. Fermi surface properties and the electronic specific heat are computed and compared with experiment. The joint density of states has also been computed and is in reasonable...... and p bands for the HCP structure. Energy bands have been evaluated both with and without spin-orbit coupling which is particularly large in thallium. Energy bands close to the Fermi level were found to be mainly 6p like in character. The 6s states lay below the 6p bands and were separated from them......The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s...

  1. Rotational band structure in 132La

    International Nuclear Information System (INIS)

    Oliveira, J.R.B.; Emediato, L.G.R.; Rizzutto, M.A.; Ribas, R.V.; Seale, W.A.; Rao, M.N.; Medina, N.H.; Botelho, S.; Cybulska, E.W.

    1989-01-01

    '3'2La was studied using on-line gamma-spectroscopy through the reactions '1 24,126 Te( 11,10 B, 3, 4n) 132 La. The excitation function was obtained with 10 B(E lab =41.4; 45.4 and 48 MeV) in order to identify 132 La gamma-transitions. Gamma-gamma coincidences and angular distributions were performed for the 126 Te( 10 B, 4n) 132 La reaction. From the experimental results a rotational band with strongest M1 transitions and less intense 'cross-overs' E2 transitions was constructed. Using the methods of Bengtsson and Frauendorf the alignment (ix) and the Routhian (e') as a function of the angular velocity (ω) were also obtained from the experimental data. It was observed a constant alignment up to ω≅0.4 MeV, and a signature-splitting Δe'=25keV. Preliminary triaxial Cranking-Shell Model calculations indicate that a γ=-8deg deformation is consistent with the signature-splitting value of 25 keV experimentally observed. (Author) [es

  2. Deformed configurations, band structures and spectroscopic ...

    Indian Academy of Sciences (India)

    2014-03-20

    Mar 20, 2014 ... Our study gives insight into possible deformed structures at spherical shell closure. ... Considerable experimental and theoretical efforts ... True deformation effects can be seen only by considering configuration mixing.

  3. Quasiparticle-phonon nuclear model

    International Nuclear Information System (INIS)

    Soloviev, V.G.

    1977-01-01

    The general assumptions of the quasiparticle-phonon model of complex nuclei are given. The choice of the model hamiltonian as an average field and residual forces is discussed. The phonon description and quasiparticle-phonon interaction are presented. The system of basic equations and their approximate solutions are obtained. The approximation is chosen so as to obtain the most correct description of few-quasiparticle components rather than of the whole wave function. The method of strenght functions is presented, which plays a decisive role in practical realization of the quasiparticle-phonon model for the description of some properties of complex nuclei. The range of applicability of the quasiparticle-phonon nuclear model is determined as few-quasiparticle components of the wave functions at low, intermediate and high excitation energies averaged in a certain energy interval

  4. Quasiparticle scattering image in hidden order phases and chiral superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Thalmeier, Peter [Max Planck Institute for Chemical Physics of Solids, 01187 Dresden (Germany); Akbari, Alireza, E-mail: alireza@apctp.org [Asia Pacific Center for Theoretical Physics, Pohang, Gyeongbuk 790-784 (Korea, Republic of); Department of Physics, and Max Planck POSTECH Center for Complex Phase Materials, POSTECH, Pohang 790-784 (Korea, Republic of)

    2016-02-15

    The technique of Bogoliubov quasiparticle interference (QPI) has been successfully used to investigate the symmetry of unconventional superconducting gaps, also in heavy fermion compounds. It was demonstrated that QPI can distinguish between the d-wave singlet candidates in CeCoIn{sub 5}. In URu{sub 2}Si{sub 2} presumably a chiral d-wave singlet superconducting (SC) state exists inside a multipolar hidden order (HO) phase. We show that hidden order leaves an imprint on the symmetry of QPI pattern that may be used to determine the essential question whether HO in URu{sub 2}Si{sub 2} breaks the in-plane rotational symmetry or not. We also demonstrate that the chiral d-wave SC gap leads to a crossover to a quasi-2D QPI spectrum below T{sub c} which sharpens the HO features. Furthermore we investigate the QPI image of chiral p-wave multigap superconductor Sr{sub 2}RuO{sub 4}. - Highlights: • The chiral multigap structure of Sr{sub 2}RuO{sub 4} leads to rotation of QPI spectrum with bias voltage. • 5f band reconstruction in hidden order phase of URu{sub 2}Si{sub 2} is obtained from two orbital model. • The chiral superconductivity in URu{sub 2}Si{sub 2} leads to quasi-2D quasiparticle interference (QPI).

  5. Quasiparticle self-consistent GW method: a short summary

    International Nuclear Information System (INIS)

    Kotani, Takao; Schilfgaarde, Mark van; Faleev, Sergey V; Chantis, Athanasios

    2007-01-01

    We have developed a quasiparticle self-consistent GW method (QSGW), which is a new self-consistent method to calculate the electronic structure within the GW approximation. The method is formulated based on the idea of a self-consistent perturbation; the non-interacting Green function G 0 , which is the starting point for GWA to obtain G, is determined self-consistently so as to minimize the perturbative correction generated by GWA. After self-consistency is attained, we have G 0 , W (the screened Coulomb interaction) and G self-consistently. This G 0 can be interpreted as the optimum non-interacting propagator for the quasiparticles. We will summarize some theoretical discussions to justify QSGW. Then we will survey results which have been obtained up to now: e.g., band gaps for normal semiconductors are predicted to a precision of 0.1-0.3 eV; the self-consistency including the off-diagonal part is required for NiO and MnO; and so on. There are still some remaining disagreements with experiments; however, they are very systematic, and can be explained from the neglect of excitonic effects

  6. Quasiparticle GW calculations for solids, molecules, and two-dimensional materials

    DEFF Research Database (Denmark)

    Hüser, Falco; Olsen, Thomas; Thygesen, Kristian Sommer

    2013-01-01

    band gap is around 1eV too low. Similar relative deviations are found for the ionization potentials of a test set of 32 small molecules. The importance of substrate screening for a correct description of quasiparticle energies and Fermi velocities in supported two-dimensional (2D) materials...... of quasiparticle states....

  7. Chromomagnetism and quasiparticles at finite temperature

    International Nuclear Information System (INIS)

    Polonyi, J.; Massachusetts Inst. of Tech., Cambridge

    1987-01-01

    The necessity for chromomagnetically charged quasiparticles in QCD is discussed. It is shown numerically that such quasiparticles are present in pure continuum QCD. Some effects of the gas of quasiparticles are conjectured. (orig.)

  8. Band structure and optical properties of opal photonic crystals

    OpenAIRE

    Pavarini, E.; Andreani, L. C.; Soci, C.; Galli, M.; Marabelli, F.; Comoretto, D.

    2005-01-01

    A theoretical approach for the interpretation of reflectance spectra of opal photonic crystals with fcc structure and (111) surface orientation is presented. It is based on the calculation of photonic bands and density of states corresponding to a specified angle of incidence in air. The results yield a clear distinction between diffraction in the direction of light propagation by (111) family planes (leading to the formation of a stop band) and diffraction in other directions by higher-order...

  9. Solving complex band structure problems with the FEAST eigenvalue algorithm

    Science.gov (United States)

    Laux, S. E.

    2012-08-01

    With straightforward extension, the FEAST eigenvalue algorithm [Polizzi, Phys. Rev. B 79, 115112 (2009)] is capable of solving the generalized eigenvalue problems representing traveling-wave problems—as exemplified by the complex band-structure problem—even though the matrices involved are complex, non-Hermitian, and singular, and hence outside the originally stated range of applicability of the algorithm. The obtained eigenvalues/eigenvectors, however, contain spurious solutions which must be detected and removed. The efficiency and parallel structure of the original algorithm are unaltered. The complex band structures of Si layers of varying thicknesses and InAs nanowires of varying radii are computed as test problems.

  10. 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.

  11. Self-consistent, relativistic, ferromagnetic band structure of gadolinium

    International Nuclear Information System (INIS)

    Harmon, B.N.; Schirber, J.; Koelling, D.D.

    1977-01-01

    An initial self-consistent calculation of the ground state magnetic band structure of gadolinium is described. A linearized APW method was used which included all single particle relativistic effects except spin-orbit coupling. The spin polarized potential was obtained in the muffin-tin form using the local spin density approximation for exchange and correlation. The most striking and unorthodox aspect of the results is the position of the 4f spin-down ''bands'' which are required to float just on top of the Fermi level in order to obtain convergence. If the 4f states (l = 3 resonance) are removed from the occupied region of the conduction bands the magnetic moment is approximately .75 μ/sub B//atom; however, as the 4f spin-down states are allowed to find their own position they hybridize with the conduction bands at the Fermi level and the moment becomes smaller. Means of improving the calculation are discussed

  12. Resonant quasiparticles in plasma turbulence

    International Nuclear Information System (INIS)

    Mendonca, J.T.; Bingham, R.; Shukla, P.K.

    2003-01-01

    A general view is proposed on wave propagation in fluids and plasmas where the resonant interaction of monochromatic waves with quasiparticles is considered. A kinetic equation for quasiparticles is used to describe the broadband turbulence interacting with monochromatic waves. Resonant interactions occur when the phase velocity of the long wavelength monochromatic wave is nearly equal to the group velocity of short wavelength wave packets, or quasiparticles, associated with the turbulent spectrum. It is shown that quasiparticle Landau damping can take place, as well as quasiparticle beam instabilities, thus establishing a direct link between short and large wavelength perturbations of the medium. This link is distinct from the usual picture of direct and inverse energy cascades, and it can be used as a different paradigm for the fluid and plasma turbulence theories

  13. Simulation of the Band Structure of Graphene and Carbon Nanotube

    International Nuclear Information System (INIS)

    Mina, Aziz N; Awadallah, Attia A; Ahmed, Riham R; Phillips, Adel H

    2012-01-01

    Simulation technique has been performed to simulate the band structure of both graphene and carbon nanotube. Accordingly, the dispersion relations for graphene and carbon nanotube are deduced analytically, using the tight binding model and LCAO scheme. The results from the simulation of the dispersion relation of both graphene and carbon nanotube were found to be consistent with those in the literature which indicates the correctness of the process of simulation technique. The present research is very important for tailoring graphene and carbon nanotube with specific band structure, in order to satisfy the required electronic properties of them.

  14. BAND STRUCTURE OF NON-STEIOCHIOMETRIC LARGE-SIZED NANOCRYSTALLITES

    Directory of Open Access Journals (Sweden)

    I.V.Kityk

    2004-01-01

    Full Text Available A band structure of large-sized (from 20 to 35nm non-steichiometric nanocrystallites (NC of the Si2-xCx (1.04 < x < 1.10 has been investigated using different band energy approaches and a modified Car-Parinello molecular dynamics structure optimization of the NC interfaces. The non-steichiometric excess of carbon favors the appearance of a thin prevailingly carbon-contained layer (with thickness of about 1 nm covering the crystallites. As a consequence, one can observe a substantial structure reconstruction of boundary SiC crystalline layers. The numerical modeling has shown that these NC can be considered as SiC reconstructed crystalline films with thickness of about 2 nm covering the SiC crystallites. The observed data are considered within the different one-electron band structure methods. It was shown that the nano-sized carbon sheet plays a key role in a modified band structure. Independent manifestation of the important role played by the reconstructed confined layers is due to the experimentally discovered excitonic-like resonances. Low-temperature absorption measurements confirm the existence of sharp-like absorption resonances originating from the reconstructed layers.

  15. Novel structural flexibility identification in narrow frequency bands

    International Nuclear Information System (INIS)

    Zhang, J; Moon, F L

    2012-01-01

    A ‘Sub-PolyMAX’ method is proposed in this paper not only for estimating modal parameters, but also for identifying structural flexibility by processing the impact test data in narrow frequency bands. The traditional PolyMAX method obtains denominator polynomial coefficients by minimizing the least square (LS) errors of frequency response function (FRF) estimates over the whole frequency range, but FRF peaks in different structural modes may have different levels of magnitude, which leads to the modal parameters identified for the modes with small FRF peaks being inaccurate. In contrast, the proposed Sub-PolyMAX method implements the LS solver in each subspace of the whole frequency range separately; thus the results identified from a narrow frequency band are not affected by FRF data in other frequency bands. In performing structural identification in narrow frequency bands, not in the whole frequency space, the proposed method has the following merits: (1) it produces accurate modal parameters, even for the modes with very small FRF peaks; (2) it significantly reduces computation cost by reducing the number of frequency lines and the model order in each LS implementation; (3) it accurately identifies structural flexibility from impact test data, from which structural deflection under any static load can be predicted. Numerical and laboratory examples are investigated to verify the effectiveness of the proposed method. (paper)

  16. Band structure of CdTe under high pressure

    International Nuclear Information System (INIS)

    Jayam, Sr. Gerardin; Nirmala Louis, C.; Amalraj, A.

    2005-01-01

    The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(E F )) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (P M = 1.935 Mbar) and the corresponding reduced volume ((V/V 0 ) M = 0.458) are estimated. Metallization occurs via direct closing of band gap at Γ point. (author)

  17. 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.

  18. Band structure analysis in SiGe nanowires

    International Nuclear Information System (INIS)

    Amato, Michele; Palummo, Maurizia; Ossicini, Stefano

    2012-01-01

    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.

  19. Optimum design of band-gap beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    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...... or significantly suppressed for a range of external excitation frequencies. Maximization of the band-gap is therefore an obvious objective for optimum design. This problem is sometimes formulated by optimizing a parameterized design model which assumes multiple periodicity in the design. However, it is shown...... in the present paper that such an a priori assumption is not necessary since, in general, just the maximization of the gap between two consecutive natural frequencies leads to significant design periodicity. The aim of this paper is to maximize frequency gaps by shape optimization of transversely vibrating...

  20. Emission bands of phosphorus and calculation of band structure of rare earth phosphides

    International Nuclear Information System (INIS)

    Al'perovich, G.I.; Gusatinskij, A.N.; Geguzin, I.I.; Blokhin, M.A.; Torbov, V.I.; Chukalin, V.I.; AN SSSR, Moscow. Inst. Novykh Khimicheskikh Problem)

    1977-01-01

    The method of x-ray emission spectroscopy has been used to investigate the electronic structure of monophosphides of rare-earth metals (REM). The fluorescence K bands of phosphorus have been obtained in LaP, PrP, SmP, GdP, TbP, DyP, HoP, ErP, TmP, YbP, and LuP and also the Lsub(2,3) bands of phosphorus in ErP, TmP, YbP, and LuP. Using the Green function technique involving the muffin-tin potential, the energy spectrum for ErP has been calculated in the single-electron approximation. The hystogram of electronic state distribution N(E) is compared with the experimental K and Lsub(2,3) bands of phosphorus in ErP. The agreement between the main details of N(E) and that of x-ray spectra allows to state that the model used provides a good description of the electron density distribution in crystals of REM monophosphides. In accordance with the character of the N(E) distribution the compounds under study are classified as semimetals or semiconductors with a very narrow forbidden band

  1. The structure of collective bands in 72Ge

    International Nuclear Information System (INIS)

    Tripathy, K.C.; Sahu, R.

    1999-01-01

    In recent years, extensive experimental studies of nuclei in the mass region A=80 have led to exciting discoveries of large ground state deformations, coexistence of shapes, band crossings, rapid variations of structure with changing nucleon numbers etc. A theoretical study of 72 Ge is presented

  2. 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...

  3. Ab-initio electronic band structure calculations for beryllium chalcogenides

    International Nuclear Information System (INIS)

    Kalpana, G.; Pari, G.; Yousuf, Mohammad

    1997-01-01

    The first principle tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground state properties, structural phase transition and pressure dependence of band gap of BeS, BeSe and BeTe. We have calculated the energy-volume relations for these compounds in the B3 and B8 phases. The calculated lattice parameters, bulk modulus and the pressure-volume relation were found to be in good agreement with the recent experimental results. The calculated B3→B8 structural transition pressure for BeS, BeSe and BeTe agree well with the recent experimental results. Our calculations show that these compounds are indirect band gap (Γ-X) semiconductors at ambient conditions. The calculated band gap values are found to be underestimated by 20-30% which is due to the usage of LDA. After the structural transition to the B8 phase, BeS continues to be indirect band gap semiconductors and ultimately above 100 GPa it metallises, BeSe and BeTe are metallic at the B3→B8 structural transition. (author)

  4. Topological Classification of Crystalline Insulators through Band Structure Combinatorics

    Science.gov (United States)

    Kruthoff, Jorrit; de Boer, Jan; van Wezel, Jasper; Kane, Charles L.; Slager, Robert-Jan

    2017-10-01

    We present a method for efficiently enumerating all allowed, topologically distinct, electronic band structures within a given crystal structure in all physically relevant dimensions. The algorithm applies to crystals without time-reversal, particle-hole, chiral, or any other anticommuting or anti-unitary symmetries. The results presented match the mathematical structure underlying the topological classification of these crystals in terms of K -theory and therefore elucidate this abstract mathematical framework from a simple combinatorial perspective. Using a straightforward counting procedure, we classify all allowed topological phases of spinless particles in crystals in class A . Employing this classification, we study transitions between topological phases within class A that are driven by band inversions at high-symmetry points in the first Brillouin zone. This enables us to list all possible types of phase transitions within a given crystal structure and to identify whether or not they give rise to intermediate Weyl semimetallic phases.

  5. Dynamical local field, compressibility, and frequency sum rules for quasiparticles

    International Nuclear Information System (INIS)

    Morawetz, Klaus

    2002-01-01

    The finite temperature dynamical response function including the dynamical local field is derived within a quasiparticle picture for interacting one-, two-, and three-dimensional Fermi systems. The correlations are assumed to be given by a density-dependent effective mass, quasiparticle energy shift, and relaxation time. The latter one describes disorder or collisional effects. This parametrization of correlations includes local-density functionals as a special case and is therefore applicable for density-functional theories. With a single static local field, the third-order frequency sum rule can be fulfilled simultaneously with the compressibility sum rule by relating the effective mass and quasiparticle energy shift to the structure function or pair-correlation function. Consequently, solely local-density functionals without taking into account effective masses cannot fulfill both sum rules simultaneously with a static local field. The comparison to the Monte Carlo data seems to support such a quasiparticle picture

  6. Electronic band structure of magnetic bilayer graphene superlattices

    International Nuclear Information System (INIS)

    Pham, C. Huy; Nguyen, T. Thuong; Nguyen, V. Lien

    2014-01-01

    Electronic band structure of the bilayer graphene superlattices with δ-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

  7. 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.

  8. Photo field emission spectroscopy of the tantalum band structure

    International Nuclear Information System (INIS)

    Kleint, Ch.; Radon, T.

    1978-01-01

    Photo field emission (PFE) currents of clean and barium covered tantalum tips have been measured with single lines of the mercury arc spectrum and phase-sensitive detection. Field strength and work function were determined from Fowler-Nordheim plots of the FE currents. Shoulders in the PFE current-voltage characteristics could be correlated to transitions in the band structure of tantalum according to a recently proposed two-step PFE model. A comparison with the relativistic calculations of Mattheiss and the nonrelativistic bands of Petroff and Viswanathan shows that Mattheiss' bands are more appropriate. Beside direct transitions several nondirect transitions from the different features composing the upper two density of states maxima below the Fermi edge of tantalum have been found. (Auth.)

  9. Configuration changes and hindered decays in four- and six-quasiparticle isomers in 178Ta

    International Nuclear Information System (INIS)

    Kondev, F.G.; Dracoulis, G.D.; Byrne, A.P.; Kibedi, T.; Bayer, S.; Lane, G.J.

    1996-01-01

    A six-quasiparticle isomer with K π =21 - , a half-life of 290(12) ms, and the π 3 ν 3 configuration has been identified in the odd-odd nucleus 178 Ta, at an excitation energy of 2902 keV. The rotational bands built on the known K π =15 - isomer and on the newly found 16 + four-quasiparticle and 22 + six-quasiparticle states, have also been identified, allowing characterization of the configurations. The 15 - band is predominantly of πν 3 character with a π 3 ν admixture. When the mixing is taken into account the excitation energies of the main yrast multi-quasiparticle states can be reproduced. The multi-quasiparticle states observed are related essentially through the addition of the two-quasiparticle component ν 2 [6 + ] or π 2 [6 + ]. Depending on whether the transition between the states involves the change ν 2 [6 + ] → [0] or π 2 [6 + ] → [0], the E2 hindrance factors for decays between the six- and four-quasiparticle states are relatively large or small. This dependence mimics the pattern observed in the two-quasiparticle core transitions and, because the 15 - isomer is mainly πν 3 , the magnitude sequence is inverted compared to that observed in 176 Ta. copyright 1996 The American Physical Society

  10. 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.

  11. Measurement of valence band structure in arbitrary dielectric films

    International Nuclear Information System (INIS)

    Uhm, Han S.; Choi, Eun H.

    2012-01-01

    A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

  12. Polarimetric and Structural Properties of a Boreal Forest at P-Band and L-Band

    Science.gov (United States)

    Tebaldini, S.; Rocca, F.

    2010-12-01

    With this paper we investigate the structural and polarimetric of the boreal forest within the Krycklan river catchment, Northern Sweden, basing on multi-polarimetric and multi-baseline SAR surveys at P-Band and L-Band collected in the framework of the ESA campaign BioSAR 2008. The analysis has been carried out by applying the Algebraic Synthesis (AS) technique, recently introduced in literature, which provides a theoretical framework for the decomposition of the backscattered signal into ground-only and volume-only contributions, basing on both baseline and polarization diversity. The availability of multiple baselines allows the formation of a synthetic aperture not only along the azimuth direction but also in elevation. Accordingly, the backscattered echoes can be focused not only in the slant range, azimuth plane, but in the whole 3D space. This is the rationale of the SAR Tomography (T-SAR) concept, which has been widely considered in the literature of the last years. It follows that, as long as the penetration in the scattering volume is guaranteed, the vertical profile of the vegetation layer is retrieved by separating backscatter contributions along the vertical direction, which is the main reason for the exploitation of Tomographic techniques at longer wavelengths. Still, the capabilities of T-SAR are limited to imaging the global vertical structure of the electromagnetic scattering in a certain polarization. It then becomes important to develop methodologies for the investigation of the vertical structure of different Scattering Mechanisms (SMs), such as ground and volume scattering, in such a way as to derive information that can be delivered also outside the field of Radar processing. This is an issue that may become relevant at longer wavelengths, such as P-Band, where the presence of multiple scattering arising from the interaction with terrain could hinder the correct reconstruction of the forest structure. The availability of multiple polarizations

  13. Mid-frequency Band Dynamics of Large Space Structures

    Science.gov (United States)

    Coppolino, Robert N.; Adams, Douglas S.

    2004-01-01

    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.

  14. Structure of the Kπ=4+ bands in Os186,188

    Science.gov (United States)

    Phillips, A. A.; Garrett, P. E.; Lo Iudice, N.; Sushkov, A. V.; Bettermann, L.; Braun, N.; Burke, D. G.; Demand, G. A.; Faestermann, T.; Finlay, P.; Green, K. L.; Hertenberger, R.; Leach, K. G.; Krücken, R.; Schumaker, M. A.; Svensson, C. E.; Wirth, H.-F.; Wong, J.

    2010-09-01

    The (He3,d) single-proton stripping reaction has been performed on targets of Re185,187 to investigate the structures of the 43+ states in Os186,188. The experiment employed 30 MeV He3 beams, and the reaction products were analyzed with a Q3D spectrograph. Absolute cross sections were determined at nine angles between 5° and 50° for states up to approximately 3 MeV in excitation energy. Large (5)/(2)+[402]π+(3)/(2)+[402]π two-quasiparticle components are deduced for the 43+ levels of both isotopes. Their magnitudes are in agreement with calculations performed using the quasiparticle phonon model, which predicts a coexistence of a large hexadecapole with a smaller, but sizable, γ-γ component in the 43+.

  15. Study of band structure of some odd proton Eu isotopes

    International Nuclear Information System (INIS)

    Pandit, Rakesh K.; Rani Devi; Khosa, S.K.

    2016-01-01

    Much work has been done on the odd-Z, odd-A nuclei in the rare earth region because of occurrence of fascinating variety of structures of nuclei in this mass region. The Eu nuclei are in the transitional deformation region and it provides an opportunity to investigate theoretically the deformation changes with mass number and excitation energy besides to study the structure of their excited states. The 153 Eu nucleus has been well studied over the last two decades. The aim of the present work is to study in detail the band structure of some odd-Z nuclei

  16. Hubbard-U band-structure methods

    DEFF Research Database (Denmark)

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

    2009-01-01

    The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many......-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...

  17. Band structure, band offsets, substitutional doping, and Schottky barriers of bulk and monolayer InSe

    Science.gov (United States)

    Guo, Yuzheng; Robertson, John

    2017-09-01

    We present a detailed study of the electronic structure of the layered semiconductor InSe. We calculate the band structure of the monolayer and bulk material using density functional theory, hybrid functionals, and G W . The band gap of the monolayer InSe is calculated to be 2.4 eV in screened exchange hybrid functional, close to the experimental photoluminescence gap. The electron affinities and band offsets are calculated for vertical stacked-layer heterostructures, and are found to be suitable for tunnel field effect transistors (TFETs) in combination with WS e2 or similar. The valence-band edge of InSe is calculated to lie 5.2 eV below the vacuum level, similar to that for the closed shell systems HfS e2 or SnS e2 . Hence InSe would be suitable to act as a p -type drain in the TFET. The intrinsic defects are calculated. For Se-rich layers, the Se adatom (interstitial) is found to be the most stable defect, whereas for In-rich layers, the Se vacancy is the most stable for the neutral state. Antisites tend to have energies just above those of vacancies. The Se antisite distorts towards a bond-breaking distortion as in the EL2 center of GaAs. Both substitutional donors and acceptors are calculated to be shallow, and effective dopants. They do not reconstruct to form nondoping configurations as occurs in black phosphorus. Finally, the Schottky barriers of metals on InSe are found to be strongly pinned by metal induced gap states (MIGS) at ˜0.5 eV above the valence-band edge. Any interfacial defects would lead to a stronger pinning at a similar energy. Overall, InSe is an effective semiconductor combining the good features of 2D (lack of dangling bonds, etc.) with the good features of 3D (effective doping), which few others achieve.

  18. Influence of the Pauli principle on the one-quasiparticle states in odd spherical nuclei

    International Nuclear Information System (INIS)

    Chan Zuy Khuong

    1980-01-01

    The effect of the Pauli principle on the fragmentation of one-quasiparticle states in odd spherical nuclei is studied within the quasiparticle-phonon nuclear model. It is shown that the Pauli principle influences considerably the position and structure of a few low-lying states. The fragmentation of one-quasiparticle states at intermediate and high excitation energies is slightly affected by the Pauli principle, and the calculations can be performed by taking the Pauli principle into account roughly. (author)

  19. Band structure and optical properties of opal photonic crystals

    Science.gov (United States)

    Pavarini, E.; Andreani, L. C.; Soci, C.; Galli, M.; Marabelli, F.; Comoretto, D.

    2005-07-01

    A theoretical approach for the interpretation of reflectance spectra of opal photonic crystals with fcc structure and (111) surface orientation is presented. It is based on the calculation of photonic bands and density of states corresponding to a specified angle of incidence in air. The results yield a clear distinction between diffraction in the direction of light propagation by (111) family planes (leading to the formation of a stop band) and diffraction in other directions by higher-order planes (corresponding to the excitation of photonic modes in the crystal). Reflectance measurements on artificial opals made of self-assembled polystyrene spheres are analyzed according to the theoretical scheme and give evidence of diffraction by higher-order crystalline planes in the photonic structure.

  20. The structure of rotational bands in alpha-cluster nuclei

    Directory of Open Access Journals (Sweden)

    Bijker Roelof

    2015-01-01

    Full Text Available In this contribution, I discuss an algebraic treatment of alpha-cluster nuclei based on the introduction of a spectrum generating algebra for the relative motion of the alpha-clusters. Particular attention is paid to the discrete symmetry of the geometric arrangement of the α-particles, and the consequences for the structure of the rotational bands in the 12C and 16O nuclei.

  1. Imaging the Nanoscale Band Structure of Topological Sb

    OpenAIRE

    Soumyanarayanan, Anjan; Yee, Michael M.; He, Yang; Lin, Hsin; Gardner, Dillon R.; Bansil, Arun; Lee, Young S.; Hoffman, Jennifer E.

    2013-01-01

    Many promising building blocks of future electronic technology - including non-stoichiometric compounds, strongly correlated oxides, and strained or patterned films - are inhomogeneous on the nanometer length scale. Exploiting the inhomogeneity of such materials to design next-generation nanodevices requires a band structure probe with nanoscale spatial resolution. To address this demand, we report the first simultaneous observation and quantitative reconciliation of two candidate probes - La...

  2. Importance of complex band structure and resonant states for tunneling

    Czech Academy of Sciences Publication Activity Database

    Dederichs, P. H.; Mavropoulos, Ph.; Wunnicke, O.; Papanikolaou, N.; Bellini, V.; Zeller, R.; Drchal, Václav; Kudrnovský, Josef

    2002-01-01

    Roč. 240, - (2002), s. 108-113 ISSN 0304-8853 R&D Projects: GA AV ČR IAA1010829; GA ČR GA202/00/0122; GA MŠk OC P5.30 Grant - others:TSR(XX) 01398 Institutional research plan: CEZ:AV0Z1010914 Keywords : magnetoresistance * tunneling * band structure * interface effects Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.046, year: 2002

  3. Band structural properties of MoS2 (molybdenite)

    International Nuclear Information System (INIS)

    Gupta, V.P.

    1980-01-01

    Semiconductivity and superconductivity in MoS 2 (molybdenite) can be understood in terms of the band structure of MoS 2 . The band structural properties of MoS 2 are presented here. The energy dependence of nsub(eff) and epsilon(infinity)sub(eff) is investigated. Using calculated values of nsub(eff) and epsilon(infinity)sub(eff), the Penn gap has been determined. The value thus obtained is shown to be in good agreement with the reflectivity data and also with the value obtained from the band structure. The Ravindra and Srivastava formula has been shown to give values for the isobaric temperature gradient of Esub(G)[(deltaEsub(G)/deltaT)sub(P)], which are in agreement with the experimental data, and the contribution to (deltaEsub(G)/deltaT)sub(P) due to the electron lattice interaction has been evaluated. In addition, the electronic polarizability has been calculated using a modified Lorentz-Lorenz relation. (author)

  4. Quasiparticle Scattering off Defects and Possible Bound States in Charge-Ordered YBa_{2}Cu_{3}O_{y}.

    Science.gov (United States)

    Zhou, R; Hirata, M; Wu, T; Vinograd, I; Mayaffre, H; Krämer, S; Horvatić, M; Berthier, C; Reyes, A P; Kuhns, P L; Liang, R; Hardy, W N; Bonn, D A; Julien, M-H

    2017-01-06

    We report the NMR observation of a skewed distribution of ^{17}O Knight shifts when a magnetic field quenches superconductivity and induces long-range charge-density-wave (CDW) order in YBa_{2}Cu_{3}O_{y}. This distribution is explained by an inhomogeneous pattern of the local density of states N(E_{F}) arising from quasiparticle scattering off, yet unidentified, defects in the CDW state. We argue that the effect is most likely related to the formation of quasiparticle bound states, as is known to occur, under specific circumstances, in some metals and superconductors (but not in the CDW state, in general, except for very few cases in 1D materials). These observations should provide insight into the microscopic nature of the CDW, especially regarding the reconstructed band structure and the sensitivity to disorder.

  5. Border Structure of Intercalary Heterochromatin Bands of Drosophila melanogaster Polytene Chromosomes.

    Science.gov (United States)

    Khoroshko, V A; Zykova, T Yu; Popova, O O; Zhimulev, I F

    2018-03-01

    The precise genomic localization of the borders of 62 intercalary heterochromatin bands in Drosophila polytene chromosomes was determined. A new type of bands containing chromatin of different states was identified. This type is a combination of the gray band and the intercalary heterochromatin band, creating a genetic structure that with a light microscope is identified as a continuous band. The border structure of such bands includes the coding regions of genes with ubiquitous activity.

  6. Band structure and unconventional electronic topology of CoSi

    Science.gov (United States)

    Pshenay-Severin, D. A.; Ivanov, Y. V.; Burkov, A. A.; Burkov, A. T.

    2018-04-01

    Semimetals with certain crystal symmetries may possess unusual electronic structure topology, distinct from that of the conventional Weyl and Dirac semimetals. Characteristic property of these materials is the existence of band-touching points with multiple (higher than two-fold) degeneracy and nonzero Chern number. CoSi is a representative of this group of materials exhibiting the so-called ‘new fermions’. We report on an ab initio calculation of the electronic structure of CoSi using density functional methods, taking into account the spin-orbit interactions. The linearized \

  7. Hybrid-DFT  +  V w method for band structure calculation of semiconducting transition metal compounds: the case of cerium dioxide.

    Science.gov (United States)

    Ivády, Viktor; Gali, Adam; Abrikosov, Igor A

    2017-11-15

    Hybrid functionals' non-local exchange-correlation potential contains a derivative discontinuity that improves on standard semi-local density functional theory (DFT) band gaps. Moreover, by careful parameterization, hybrid functionals can provide self-interaction reduced description of selected states. On the other hand, the uniform description of all the electronic states of a given system is a known drawback of these functionals that causes varying accuracy in the description of states with different degrees of localization. This limitation can be remedied by the orbital dependent exact exchange extension of hybrid functionals; the hybrid-DFT  +  V w method (Ivády et al 2014 Phys. Rev. B 90 035146). Based on the analogy of quasi-particle equations and hybrid-DFT single particle equations, here we demonstrate that parameters of hybrid-DFT  +  V w functional can be determined from approximate theoretical quasi-particle spectra without any fitting to experiment. The proposed method is illustrated on the charge self-consistent electronic structure calculation for cerium dioxide where itinerant valence states interact with well-localized 4f atomic like states, making this system challenging for conventional methods, either hybrid-DFT or LDA  +  U, and therefore allowing for a demonstration of the advantages of the proposed scheme.

  8. Particle-number conserving analysis for the 2-quasiparticle and high-K multi-quasiparticle states in doubly-odd 174,176Lu

    International Nuclear Information System (INIS)

    Li Bingheng; Lei Yi'an; Zhang Zhenhua

    2013-01-01

    Two-quasiparticle bands and low-lying excited high-K four-, six-, and eight-quasiparticle bands in the doubly-odd 174,176 Lu are analyzed by using the cranked shell model (CSM) with the pairing correlations treated by a particle-number conserving (PNC) method, in which the blocking effects are taken into account exactly. The proton and neutron Nilsson level schemes for 174,176 Lu are taken from the adjacent odd-A Lu and Hf isotopes, which are adopted to reproduce the experimental bandhead energies of the one-quasiproton and one-quasineutron bands of these odd-A Lu and Hf nuclei, respectively. Once the quasiparticle configurations are determined, the experimental bandhead energies and the moments of inertia of these two- and multi-quasiparticle bands are well reproduced by PNC-CSM calculations. The Coriolis mixing of the low-K (K=|Ω 1 -Ω 2 |) two-quasiparticle band of the Gallagher-Moszkowski doublet with one nucleon in the Ω=1/2 orbital is analyzed. (authors)

  9. Band structure of hydrogenated Si nanosheets and nanotubes

    International Nuclear Information System (INIS)

    Guzman-Verri, G G; Lew Yan Voon, L C

    2011-01-01

    The band structures of fully hydrogenated Si nanosheets and nanotubes are elucidated by the use of an empirical tight-binding model. The hydrogenated Si sheet is a semiconductor with an indirect band gap of about 2.2 eV. The symmetries of the wavefunctions allow us to explain the origin of the gap. We predict that, for certain chiralities, hydrogenated Si nanotubes represent a new type of semiconductor, one with coexisting direct and indirect gaps of exactly the same magnitude. This behavior is different from that governed by the Hamada rule established for non-hydrogenated carbon and silicon nanotubes. A comparison to the results of an ab initio calculation is made.

  10. Valence band electronic structure of Pd based ternary chalcogenide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lohani, H. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India); Mishra, P. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Goyal, R.; Awana, V.P.S. [National Physical Laboratory(CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Sekhar, B.R., E-mail: sekhar@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India)

    2016-12-15

    Highlights: • VB Photoemission study and DFT calculations on Pd based ternary superconductors are presented. • Nb{sub 2}Pd{sub 0.95}S{sub 5} shows a temperature dependent pseudogap. • VB spectral features of ternary superconductors are correlated to their structural geometry. - Abstract: We present a comparative study of the valence band electronic structure of Pd based ternary chalcogenide superconductors Nb{sub 2}Pd{sub 0.95}S{sub 5}, Ta{sub 2}Pd{sub 0.97}S{sub 6} and Ta{sub 2}Pd{sub 0.97}Te{sub 6} using experimental photoemission spectroscopy and density functional based theoretical calculations. We observe a qualitatively similarity between valence band (VB) spectra of Nb{sub 2}Pd{sub 0.95}S{sub 5} and Ta{sub 2}Pd{sub 0.97}S{sub 6}. Further, we find a pseudogap feature in Nb{sub 2}Pd{sub 0.95}S{sub 5} at low temperature, unlike other two compounds. We have correlated the structural geometry with the differences in VB spectra of these compounds. The different atomic packing in these compounds could vary the strength of inter-orbital hybridization among various atoms which leads to difference in their electronic structure as clearly observed in our DOS calculations.

  11. Transport quasiparticles and transverse interactions in quark-gluon plasmas

    International Nuclear Information System (INIS)

    Baym, Gordon

    1996-01-01

    Calculations of the properties of interacting quark-gluon plasmas are beset by infrared divergences associated with the fact that magnetic interactions, i.e., those occurring through exchange of transverse gluons, are, in the absence of a 'magnetic mass''in QCD, not screened. In this lecture we discuss the effects of magnetic interactions on the transport coefficients and the quasiparticle structure of quark-gluon plasmas. We describe how inclusion of dynamical screening effects - corresponding to Landau damping of the virtual quanta exchanged - leads to finite transport scattering rates. In the weak coupling limit, dynamical screening effects dominate over a magnetic mass. We illustrate the breakdown of the quasi particle structure of degenerate plasmas caused by long-ranged magnetic interactions, describe the structure of fermion quasiparticles in hot relativistic plasmas, and touch briefly on the problem of the lifetime of quasiparticle in the presence of long-ranged magnetic interactions. (author)

  12. Role of quasiparticle x phonon components in gamma-decay of hogh-lying states

    International Nuclear Information System (INIS)

    Ponomarev, V.Yu.; Solov'ev, V.G.; Vdovin, A.I.; Stoyanov, Ch.

    1986-01-01

    In the framework of quasiparticle-phonon model of a nucleus the probabilities of gamma-transitions (E1, M1, E2) from a high-lying resonance-similar structure to the excitation of neutron hole state (lg 9/2 ) -1 of 111 Sn nucleus to the main and low-excited one-quasiparticle states have been calculated. Wave function of a highly excited state comprised the components ''quasiparticle x phonon'' and ''quasiparticle x two phonons''. For E1-transitions 9/2 + → 11/2 1 - the main contribution to the transition is made by one-quasiparticle components of wave functions of the initial and final states. E2-transition 9/2 + → 7/2 g,s + takes place at the expense of impurities in ''quasiparticle x phonon'' states. For M1-transition from the states 9/2 + to the main one a strong destructive interference of contributions of one-quasiparticle and ''quasiparticle x phonon'' components is observed. Thus it is shown that components ''quasiparticle x phonon'' may play the major role in correct description of gamma-transitions from high-lying one-particle or low-lying hole states

  13. Band structure engineering for ultracold quantum gases in optical lattices

    International Nuclear Information System (INIS)

    Weinberg, Malte

    2014-01-01

    The energy band structure fundamentally influences the physical properties of a periodic system. It may give rise to highly exotic phenomena in yet uncharted physical regimes. Ultracold quantum gases in optical lattices provide an ideal playground for the investigation of a large variety of such intriguing effects. Experiments presented here address several issues that require the systematic manipulation of energy band structures in optical lattices with diverse geometries. These artificial crystals of light, generated by interfering laser beams, allow for an unprecedented degree of control over a wide range of parameters. A major part of this thesis employs time-periodic driving to engineer tunneling matrix elements and, thus, the dispersion relation for bosonic quantum gases in optical lattices. Resonances emerging in the excitation spectrum due to the particularly strong forcing can be attributed to multi-photon transitions that are investigated systematically. By changing the sign of the tunneling, antiferromagnetic spin-spin interactions can be emulated. In a triangular lattice this leads to geometrical frustration with a doubly degenerate ground state as the simultaneous minimization of competing interactions is inhibited. Moreover, complex-valued tunneling matrix elements can be generated with a suitable breaking of time-reversal symmetry in the driving scheme. The associated Peierls phases mimic the presence of an electromagnetic vector gauge potential acting on charged particles. First proof-of-principle experiments reveal an excellent agreement with theoretical calculations. In the weakly interacting superfluid regime, these artificial gauge fields give rise to an Ising-XY model with tunable staggered magnetic fluxes and a complex interplay between discrete and continuous symmetries. A thermal phase transition from an ordered ferromagnetic- to an unordered paramagnetic state could be observed. In the opposite hard-core boson limit of strong interactions

  14. Quasiparticle interaction in nuclear matter

    International Nuclear Information System (INIS)

    Poggioli, R.S.; Jackson, A.D.

    1975-07-01

    A microscopic calculation of the quasiparticle interaction in nuclear matter is detailed. In order to take especial care of the contributions from the low momentum states, a model space is introduced. Excluded from the model space, the high momentum states are absorbed into the model interaction. Brueckner theory suggests the choice of a truncated G-matrix as a good approximation for this model interaction. A simple perturbative approach is attempted within the model space. The calculated quasiparticle interaction is consistent with experimental results. (11 tables, 14 figures)

  15. Band structure in Platinum nuclei (A ∼ 182)

    International Nuclear Information System (INIS)

    Popescu, D.G.

    1991-01-01

    In this thesis, the author studies the band structure in Platinum nuclei and has divided his work in 5 parts: in the first, the author makes a general presentation of nucleus physics with a high angular momentum and introduces to the deformed nucleus notion -axial, triaxial or mixing of different deformations. The notion of form co-existence will be used to interpret the experimental results. In the second part, the author describes the detection means which have been used to make measurements. An abstract of theoretical notions, usefull for the understanding of fusion-evaporation reaction is presented. The author explains the details, performances and different modes of using of 'Chateau de cristal' and others used spectrometers. In the third part, the author presents all experimental data. He has effected γ coincidence measurements for Pt, Au and Ir nuclei. In the fourth part, for a classical analysis or an interpretation in the frame of cranking model the author presents theoretical models which are adapted at the study of high spin states and band structures

  16. Photonic band structure calculations using nonlinear eigenvalue techniques

    International Nuclear Information System (INIS)

    Spence, Alastair; Poulton, Chris

    2005-01-01

    This paper considers the numerical computation of the photonic band structure of periodic materials such as photonic crystals. This calculation involves the solution of a Hermitian nonlinear eigenvalue problem. Numerical methods for nonlinear eigenvalue problems are usually based on Newton's method or are extensions of techniques for the standard eigenvalue problem. We present a new variation on existing methods which has its derivation in methods for bifurcation problems, where bordered matrices are used to compute critical points in singular systems. This new approach has several advantages over the current methods. First, in our numerical calculations the new variation is more robust than existing techniques, having a larger domain of convergence. Second, the linear systems remain Hermitian and are nonsingular as the method converges. Third, the approach provides an elegant and efficient way of both thinking about the problem and organising the computer solution so that only one linear system needs to be factorised at each stage in the solution process. Finally, first- and higher-order derivatives are calculated as a natural extension of the basic method, and this has advantages in the electromagnetic problem discussed here, where the band structure is plotted as a set of paths in the (ω,k) plane

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

    DEFF Research Database (Denmark)

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

    2005-01-01

    in electromagnetic and microwave applications once the Maxwell's equations are appropriately modeled. Originality/value - The method validates its values and properties through extensive studies on regular and defective 1D PBG structures in stratified medium, and it can be further extended to solving more......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...... in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT) properties to expand the spatial derivatives in Maxwell's equations. In addition, the method makes use of the chain-rule property in calculus together...

  18. Quasi-particle energies and optical excitations of hydrogenated and fluorinated germanene.

    Science.gov (United States)

    Shu, Huabing; Li, Yunhai; Wang, Shudong; Wang, Jinlan

    2015-02-14

    Using density functional theory, the G0W0 method and Bethe-Salpeter equation calculations, we systematically explore the structural, electronic and optical properties of hydrogenated and fluorinated germanene. The hydrogenated/fluorinated germanene tends to form chair and zigzag-line configurations and its electronic and optical properties show close geometry dependence. The chair hydrogenated/fluorinated and zigzag-line fluorinated germanene are direct band-gap semiconductors, while the zigzag-line hydrogenated germanene owns an indirect band-gap. Moreover, the quasi-particle corrections are significant and strong excitonic effects with large exciton binding energies are observed. Moreover, the zigzag-line hydrogenated/fluorinated germanene shows highly anisotropic optical responses, which may be used as a good optical linear polarizer.

  19. Quasiparticle energies, excitons, and optical spectra of few-layer black phosphorus

    International Nuclear Information System (INIS)

    Tran, Vy; Fei, Ruixiang; Yang, Li

    2015-01-01

    We report first-principles GW–Bethe–Salpeter-equation (BSE) studies of excited-state properties of few-layer black phosphorus (BP) (phosphorene). With improved GW computational methods, we obtained converged quasiparticle band gaps and optical absorption spectra by the single-shot (G 0 W 0 ) procedure. Moreover, we reveal fine structures of anisotropic excitons, including the series of one-dimensional like wave functions, spin singlet–triplet splitting, and electron–hole binding energy spectra by solving BSE. An effective-mass model is employed to describe these electron–hole pairs, shedding light on estimating the exciton binding energy of anisotropic two-dimensional semiconductors without expensive ab initio simulations. Finally, the anisotropic optical response of BP is explained by using optical selection rules based on the projected single-particle density of states at band edges. (paper)

  20. Study of band structure in 78,80Sr using Triaxial Projected Shell Model

    International Nuclear Information System (INIS)

    Behera, N.; Naik, Z.; Bhat, G.H.; Sheikh, J.A.; Palit, R.; Sun, Y.

    2017-01-01

    The purpose of present work is to carry out a systematic study of the yrast-band and gamma-band structure for the even-even 78-80 Sr nuclei using Triaxial Projected Shell Model (TPSM) approach. These nuclei were chosen because 78 Sr has well developed side band(unassigned configuration) and 80 Sr has well developed band observed experimentally

  1. 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).

  2. Quasiparticle Scattering in the Rashba Semiconductor BiTeBr: The Roles of Spin and Defect Lattice Site.

    Science.gov (United States)

    Butler, Christopher John; Yang, Po-Ya; Sankar, Raman; Lien, Yen-Neng; Lu, Chun-I; Chang, Luo-Yueh; Chen, Chia-Hao; Wei, Ching-Ming; Chou, Fang-Cheng; Lin, Minn-Tsong

    2016-09-28

    Observations of quasiparticle interference have been used in recent years to examine exotic carrier behavior at the surfaces of emergent materials, connecting carrier dispersion and scattering dynamics to real-space features with atomic resolution. We observe quasiparticle interference in the strongly Rashba split 2DEG-like surface band found at the tellurium termination of BiTeBr and examine two mechanisms governing quasiparticle scattering: We confirm the suppression of spin-flip scattering by comparing measured quasiparticle interference with a spin-dependent elastic scattering model applied to the calculated spectral function. We also use atomically resolved STM maps to identify point defect lattice sites and spectro-microscopy imaging to discern their varying scattering strengths, which we understand in terms of the calculated orbital characteristics of the surface band. Defects on the Bi sublattice cause the strongest scattering of the predominantly Bi 6p derived surface band, with other defects causing nearly no scattering near the conduction band minimum.

  3. Characterization of band structure for transverse acoustic phonons in Fibonacci superlattices by a bandedge formalism

    International Nuclear Information System (INIS)

    Hsueh, W J; Chen, R F; Tang, K Y

    2008-01-01

    We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.

  4. Band structure of ABC-trilayer graphene superlattice

    International Nuclear Information System (INIS)

    Uddin, Salah; Chan, K. S.

    2014-01-01

    We investigate the effect of one-dimensional periodic potentials on the low energy band structure of ABC trilayer graphene first by assuming that all the three layers have the same potential. Extra Dirac points having the same electron hole crossing energy as that of the original Dirac point are generated by superlattice potentials with equal well and barrier widths. When the potential height is increased, the numbers of extra Dirac points are increased. The dispersions around the Dirac points are not isotropic. It is noted that the dispersion along the k y direction for k x  = 0 oscillates between a non-linear dispersion and a linear dispersion when the potential height is increased. When the well and barrier widths are not identical, the symmetry of the conduction and valence bands is broken. The extra Dirac points are shifted either upward or downward depending on the barrier and well widths from the zero energy, while the position of the central Dirac point oscillates with the superlattice potential height. By considering different potentials for different layers, extra Dirac points are generated not from the original Dirac points but from the valleys formed in the energy spectrum. Two extra Dirac points appear from each pair of touched valleys, so four Dirac points appeared in the spectrum at particular barrier height. By increasing the barrier height of superlattice potential two Dirac points merge into the original Dirac point. This emerging and merging of extra Dirac points is different from the equal potential case

  5. 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....

  6. Band structure and optical properties of diglycine nitrate crystal

    International Nuclear Information System (INIS)

    Andriyevsky, Bohdan; Ciepluch-Trojanek, Wioleta; Romanyuk, Mykola; Patryn, Aleksy; Jaskolski, Marcin

    2005-01-01

    Experimental and theoretical investigations of the electron energy characteristics and optical spectra for diglycine nitrate crystal (DGN) (NH 2 CH 2 COOH) 2 .HNO 3 , in the paraelectric phase (T=295K) are presented. Spectral dispersion of light reflection R(E) have been measured in the range of 3-22eV and the optical functions n(E) and k(E) have been calculated using Kramers-Kronig relations. First principal calculations of the electron energy characteristic and optical spectra of DGN crystal have been performed in the frame of density functional theory using CASTEP code (CAmbridge Serial Total Energy Package). Optical transitions forming the low-energy edge of fundamental absorption are associated with the nitrate groups NO 3 . Peculiarities of the band structure and DOS projected onto glycine and NO 3 groups confirm the molecular character of DGN crystal

  7. Phononic Band Gaps in 2D Quadratic and 3D Cubic Cellular Structures.

    Science.gov (United States)

    Warmuth, Franziska; Körner, Carolin

    2015-12-02

    The static and dynamic mechanical behaviour of cellular materials can be designed by the architecture of the underlying unit cell. In this paper, the phononic band structure of 2D and 3D cellular structures is investigated. It is shown how the geometry of the unit cell influences the band structure and eventually leads to full band gaps. The mechanism leading to full band gaps is elucidated. Based on this knowledge, a 3D cellular structure with a broad full band gap is identified. Furthermore, the dependence of the width of the gap on the geometry parameters of the unit cell is presented.

  8. Brownian quasi-particles and quantum quasi-particles

    International Nuclear Information System (INIS)

    Fronteau, J.

    1987-01-01

    The concept of quasi-particles is used in Statistical Mechanics as well as in Quantum Mechanics, to associate differentiable trajectories to the equations of evolution, trajectories on which a maximum of informations is concentrated concerning the phenomena studied. Two cases are treated numerically, that of the Fokker-Planck equation with an x - x 3 field, and that of the Schroedinger equation with null potential, in a situation of interference [fr

  9. Surface correlation effects in two-band strongly correlated slabs.

    Science.gov (United States)

    Esfahani, D Nasr; Covaci, L; Peeters, F M

    2014-02-19

    Using an extension of the Gutzwiller approximation for an inhomogeneous system, we study the two-band Hubbard model with unequal band widths for a slab geometry. The aim is to investigate the mutual effect of individual bands on the spatial distribution of quasi-particle weight and charge density, especially near the surface of the slab. The main effect of the difference in band width is the presence of two different length scales corresponding to the quasi-particle profile of each band. This is enhanced in the vicinity of the critical interaction of the narrow band where an orbitally selective Mott transition occurs and a surface dead layer forms for the narrow band. For the doped case, two different regimes of charge transfer between the surface and the bulk of the slab are revealed. The charge transfer from surface/center to center/surface depends on both the doping level and the average relative charge accumulated in each band. Such effects could also be of importance when describing the accumulation of charges at the interface between structures made of multi-band strongly correlated materials.

  10. 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

  11. Photonic band edge assisted spontaneous emission enhancement from all Er3+ 1-D photonic band gap structure

    Science.gov (United States)

    Chiasera, A.; Meroni, C.; Varas, S.; Valligatla, S.; Scotognella, F.; Boucher, Y. G.; Lukowiak, A.; Zur, L.; Righini, G. C.; Ferrari, M.

    2018-06-01

    All Er3+ doped dielectric 1-D Photonic Band Gap Structure was fabricated by rf-sputtering technique. The structure was constituted by of twenty pairs of SiO2/TiO2 alternated layers doped with Er3+ ions. The scanning electron microscopy was used to check the morphology of the structure. Transmission measurements put in evidence the stop band in the range 1500 nm-1950 nm. The photoluminescence measurements were obtained by optically exciting the sample and detecting the emitted light in the 1.5 μm region at different detection angles. Luminescence spectra and luminescence decay curves put in evidence that the presence of the stop band modify the emission features of the Er3+ ions.

  12. 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.......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....

  13. The effect of the Pauli principle on the fragmentation of one-quasiparticle states in spherical nuclei

    International Nuclear Information System (INIS)

    Khuong, C.Z.; Soloviev, V.G.; Voronov, V.V.

    1981-01-01

    The effect of the Pauli principle on the fragmentation of one-quasiparticle states in spherical nuclei is studied within the quasiparticle-phonon nuclear model. It is shown that the Pauli principle influences considerably the position and structure of a few low-lying states, the fragmentation of one-quasiparticle states at intermediate and high excitation energies is slightly affected by the Pauli principle, and the calculations can be performed by taking the Pauli principle roughly into account. (author)

  14. Four-quasiparticle isomers and K-forbidden transitions in 176Lu

    International Nuclear Information System (INIS)

    McGoram, T.R.; Dracoulis, G.D.; Kibedi, T.; Mullins, M.; Byrne, A.P.; Baxter, A.M.

    2000-01-01

    Full text: The odd-odd nucleus 176 Lu has been the subject of extensive experimental and theoretical investigation over the last forty years. Much of this interest has stemmed from the role of 176 Lu in the s-process in nucleosynthesis. From a nuclear structure perspective, 176 Lu resides in a region of the nuclear chart where collective rotation and high-K, multi-quasiparticle states compete to form the yrast line (the locus of state with the lowest energy at a given angular momentum). The electromagnetic decay of intermediate and high-K states is often hindered due to the K-selection rule, while apparent violations of this selection rule have been ascribed to Coriolis mixing, shape changes in the gamma-degree of freedom, and so-called 'statistical' mixing. The relative importance of these mechanisms remains an open question. We present here the results of gamma-ray and conversion-electron spectroscopic measurements, performed at the Heavy Ion Facility at the Australian National University in Canberra, using the reaction 176 Yb( 7 Li, α3n) at a beam energy of 45 MeV. Two new four-quasiparticle isomers have been established, with mean lives of 400(100)ns and 58(5)μs, and spin projections and parities of 12 + and (14 + ) respectively. The shorter--lived isomer displays both normal and anomalous K-forbidden decays, which we show is the result of two-state mixing between the isomeric state and a member of a two-quasiparticle rotational band. The implied mixing matrix element of only 5 eV shows explicitly that very small mixing matrix elements may be responsible for anomalous K-hindered decays

  15. Design of an X-band accelerating structure using a newly developed structural optimization procedure

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Xiaoxia [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Fang, Wencheng; Gu, Qiang [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhao, Zhentang, E-mail: zhaozhentang@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China)

    2017-05-11

    An X-band high gradient accelerating structure is a challenging technology for implementation in advanced electron linear accelerator facilities. The present work discusses the design of an X-band accelerating structure for dedicated application to a compact hard X-ray free electron laser facility at the Shanghai Institute of Applied Physics, and numerous design optimizations are conducted with consideration for radio frequency (RF) breakdown, RF efficiency, short-range wakefields, and dipole/quadrupole field modes, to ensure good beam quality and a high accelerating gradient. The designed X-band accelerating structure is a constant gradient structure with a 4π/5 operating mode and input and output dual-feed couplers in a racetrack shape. The design process employs a newly developed effective optimization procedure for optimization of the X-band accelerating structure. In addition, the specific design of couplers providing high beam quality by eliminating dipole field components and reducing quadrupole field components is discussed in detail.

  16. Charge of a quasiparticle in a superconductor.

    Science.gov (United States)

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-02-16

    Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure.

  17. Determination of conduction and valence band electronic structure ...

    Indian Academy of Sciences (India)

    shifts in the rutile Ti d-band to lower energy with respect to anatase, i.e., ... requires excitation with UV light due to its wide band ... RIXS maps were compared to the theoretical results .... optical methods are insufficient, such as dark samples.

  18. Rietveld analysis and electronic bands structure on Tc superconductors systems

    International Nuclear Information System (INIS)

    Aldea, N.; Tiusan, C. V.; Sandu, V.

    1999-01-01

    A procedure for simultaneous refinement of structural and micro-structural disorder parameters for polycrystalline YBa 2 Cu 3 O 7-x system is proposed. It is based on Rietveld method combined with Fourier analysis for broadened peaks Another purpose of this paper consists in electronic structure determination studied by using the self-consistent Tight Binding Linear Muffin-Tin Orbital Atomic Spheres Approximation TB-LMTO-ASA methods. The Rietveld method uses an analytical function that describes the profiles, usually pseudo-Voigt (pV) or Pearson VII (PVII). The parameters of the analytical profiles describe its amplitude, position and peak shape. The full width at half maximum (FWHM) is supposed to vary with the diffraction angle in agreement with the Caglioti, Paoletti and Ricci's relationship. The best structural parameters are determined in the least squares sense by the minimisation a classical residual using the Marquardt method. In this case, the peak profiles were modelled by the pseudo-Voigt function corrected by the instrumental asymmetry. The physical information obtained are: scale factor, lattice parameters, atomic position and displacements, atomic occupation numbers, temperature factor (isotropy or anisotropy), preferred orientation parameter, crystalline size and micro-strain along different crystallographic directions, distributions of crystallite size and micro-strain functions. This procedure was implemented on computer code and it has a friendly graphical interface based on pull down menus technique. From the experimental point of view the X-ray diffraction data were collected using a horizontal powder diffractometer in the Bragg-Brentano (BB) geometry with a Ni filtered CuKα, λ = 1.54178 A, at room temperature using a DRON 2 set-up. The diffraction profiles were measured with a proportional gas detector, a single channel pulse-height discrimination and a standard associated counting circuit. The electronic band calculations are based on the TB

  19. Tunable band structures in digital oxides with layered crystal habits

    Science.gov (United States)

    Shin, Yongjin; Rondinelli, James M.

    2017-11-01

    We use density functional calculations to show that heterovalent cation-order sequences enable control over band-gap variations up to several eV and band-gap closure in the bulk band insulator LaSrAlO4. The band-gap control originates from the internal electric fields induced by the digital chemical order, which induces picoscale band bending; the electric-field magnitude is mainly governed by the inequivalent charged monoxide layers afforded by the layered crystal habit. Charge transfer and ionic relaxations across these layers play secondary roles. This understanding is used to construct and validate a descriptor that captures the layer-charge variation and to predict changes in the electronic gap in layered oxides exhibiting antisite defects and in other chemistries.

  20. Electronic structure of SnS deduced from photoelectron spectra and band-structure calculations

    NARCIS (Netherlands)

    Ettema, A.R.H.F.; Groot, R.A. de; Haas, C.; Turner, T.S.

    1992-01-01

    SnS is a layer compound with a phase transition from a high-temperature β phase to a low-temperature α phase with a lower symmetry. Ab initio band-structure calculations are presented for both phases. The calculations show that the charge distributions in the two phases are very similar. However,

  1. Brownian quasi-particles in statistical physics

    International Nuclear Information System (INIS)

    Tellez-Arenas, A.; Fronteau, J.; Combis, P.

    1979-01-01

    The idea of a Brownian quasi-particle and the associated differentiable flow (with nonselfadjoint forces) are used here in the context of a stochastic description of the approach towards statistical equilibrium. We show that this quasi-particle flow acquires, at equilibrium, the principal properties of a conservative Hamiltonian flow. Thus the model of Brownian quasi-particles permits us to establish a link between the stochastic description and the Gibbs description of statistical equilibrium

  2. Quasiparticles in non-uniformly magnetized plasma

    International Nuclear Information System (INIS)

    Sosenko, P.P.

    1994-01-01

    A quasiparticle concept is generalized for the case of non-uniformly magnetized plasma. Exact and reduced continuity equations for the microscopic density in the quasiparticle phase space are derived, and the nature of quasiparticles is analyzed. The theory is developed for the general case of relativistic particles in electromagnetic fields, besides non-uniform but stationary magnetic fields. Effects of non-stationary magnetic fields are briefly investigated also. 26 refs

  3. Electronic band structure in porous silicon studied by photoluminescence and photoluminescence excitation spectroscopy

    International Nuclear Information System (INIS)

    Lee, Ki-Won; Kim, Young-You

    2004-01-01

    In this research, we used photoluminescence (PL) and photoluminescence excitation (PLE) to visualize the electronic band structure in porous silicon (PS). From the combined results of the PLE measurements at various PL emission energies and the PL measurements under excitation at various PLE absorption energies, we infer that three different electronic band structures, originating from different luminescent origins, give rise to the PL spectrum. Through either thermal activation or diffusive transfer, excited carriers are moved to each of the electronic band structures.

  4. Stretched horizons, quasiparticles, and quasinormal modes

    International Nuclear Information System (INIS)

    Iizuka, Norihiro; Kabat, Daniel; Lifschytz, Gilad; Lowe, David A.

    2003-01-01

    We propose that stretched horizons can be described in terms of a gas of noninteracting quasiparticles. The quasiparticles are unstable, with a lifetime set by the imaginary part of the lowest quasinormal mode frequency. If the horizon arises from an AdS-CFT style duality the quasiparticles are also the effective low-energy degrees of freedom of the finite-temperature CFT. We analyze a large class of models including Schwarzschild black holes, nonextremal Dp-branes, the rotating BTZ black hole and de Sitter space, and we comment on degenerate horizons. The quasiparticle description makes manifest the relationship between entropy and area

  5. Hidden order symmetry and superconductivity in heavy Fermions investigated by quasiparticle interference

    Energy Technology Data Exchange (ETDEWEB)

    Akbari, Alireza [Asia Pacific Center for Theoretical Physics, POSTECH, Pohang, Gyeongbuk 790-784 (Korea, Republic of); MPI for Solid State Research, Stuttgart (Germany); Thalmeier, Peter [MPI for the Chemical Physics of Solids, Dresden (Germany)

    2015-07-01

    The hidden order (HO) in URu{sub 2}Si{sub 2} has been determined as a high rank multipole formed by itinerant 5f-electrons with distinct orbital structure imposed by the crystalline electric field. Because this can lead to a considerable number of different multipoles it is of great importance to use microscopic techniques that are sensitive to their subtle physical differences. Here we investigate whether quasiparticle interference (QPI) method can distinguish between the two most frequently proposed HO parameter models: the even rank-4 hexadecapole and the odd-rank-5 dotriacontapole model. We obtain the quasiparticle dispersion and reconstructed Fermi surface in each HO phase adapting an effective two-orbital model of 5f bands that reproduces the main Fermi surface sheets of the para phase. We show that the resulting QPI spectrum reflects directly the effect of fourfold symmetry breaking in the rank-5 model which is absent in the rank-4 model. Therefore we suggest that QPI method should give a possibility of direct discrimination between the two most investigated models of HO in URu{sub 2}Si{sub 2}. Furthermore the signature of proposed chiral d-wave superconducting (SC) order parameter in QPI of the coexisting HO+SC phase is investigated.

  6. Multi-quasiparticle excitations in 145Tb

    International Nuclear Information System (INIS)

    Zheng Yong; Zhou Xiaohong; Zhang Yuhu; Liu Minliang; Guo Yingxiang; Lei Xiangguo; Kusakari, H.; Sugawara, M.

    2004-01-01

    High-spin states in 145 Tb have been populated using the 118 Sn( 32 S, 1p4n) reaction at a beam energy of 165 MeV. The level scheme of 145 Tb has been established for the first time. The level scheme shows characteristics of spherical or slightly oblate nucleus. Based on the systematic trends of the level structure in the neighboring N=80 isotones, the level structure in 145 Tb below 2 MeV excitation is well explained by coupling an h 11/2 valence proton to the even-even 144 Gd core. Above 2 MeV excitation, most of the yrast levels are interpreted with multi-quasiparticle shell-model configurations. (authors)

  7. Band structure of an electron in a kind of periodic potentials with singularities

    Science.gov (United States)

    Hai, Kuo; Yu, Ning; Jia, Jiangping

    2018-06-01

    Noninteracting electrons in some crystals may experience periodic potentials with singularities and the governing Schrödinger equation cannot be defined at the singular points. The band structure of a single electron in such a one-dimensional crystal has been calculated by using an equivalent integral form of the Schrödinger equation. Both the perturbed and exact solutions are constructed respectively for the cases of a general singular weak-periodic system and its an exactly solvable version, Kronig-Penney model. Any one of them leads to a special band structure of the energy-dependent parameter, which results in an effective correction to the previous energy-band structure and gives a new explanation for forming the band structure. The used method and obtained results could be a valuable aid in the study of energy bands in solid-state physics, and the new explanation may trigger investigation to different physical mechanism of electron band structures.

  8. Optical model with multiple band couplings using soft rotator structure

    Science.gov (United States)

    Martyanov, Dmitry; Soukhovitskii, Efrem; Capote, Roberto; Quesada, Jose Manuel; Chiba, Satoshi

    2017-09-01

    A new dispersive coupled-channel optical model (DCCOM) is derived that describes nucleon scattering on 238U and 232Th targets using a soft-rotator-model (SRM) description of the collective levels of the target nucleus. SRM Hamiltonian parameters are adjusted to the observed collective levels of the target nucleus. SRM nuclear wave functions (mixed in K quantum number) have been used to calculate coupling matrix elements of the generalized optical model. Five rotational bands are coupled: the ground-state band, β-, γ-, non-axial- bands, and a negative parity band. Such coupling scheme includes almost all levels below 1.2 MeV of excitation energy of targets. The "effective" deformations that define inter-band couplings are derived from SRM Hamiltonian parameters. Conservation of nuclear volume is enforced by introducing a monopolar deformed potential leading to additional couplings between rotational bands. The present DCCOM describes the total cross section differences between 238U and 232Th targets within experimental uncertainty from 50 keV up to 200 MeV of neutron incident energy. SRM couplings and volume conservation allow a precise calculation of the compound-nucleus (CN) formation cross sections, which is significantly different from the one calculated with rigid-rotor potentials with any number of coupled levels.

  9. Lightwave-driven quasiparticle collisions on a subcycle timescale.

    Science.gov (United States)

    Langer, F; Hohenleutner, M; Schmid, C P; Poellmann, C; Nagler, P; Korn, T; Schüller, C; Sherwin, M S; Huttner, U; Steiner, J T; Koch, S W; Kira, M; Huber, R

    2016-05-12

    Ever since Ernest Rutherford scattered α-particles from gold foils, collision experiments have revealed insights into atoms, nuclei and elementary particles. In solids, many-body correlations lead to characteristic resonances--called quasiparticles--such as excitons, dropletons, polarons and Cooper pairs. The structure and dynamics of quasiparticles are important because they define macroscopic phenomena such as Mott insulating states, spontaneous spin- and charge-order, and high-temperature superconductivity. However, the extremely short lifetimes of these entities make practical implementations of a suitable collider challenging. Here we exploit lightwave-driven charge transport, the foundation of attosecond science, to explore ultrafast quasiparticle collisions directly in the time domain: a femtosecond optical pulse creates excitonic electron-hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying dynamics of the wave packets, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands of the optical excitation. A full quantum theory explains our observations microscopically. This approach enables collision experiments with various complex quasiparticles and suggests a promising new way of generating sub-femtosecond pulses.

  10. Interlayer Excitons and Band Alignment in MoS2/hBN/WSe2 van der Waals Heterostructures

    DEFF Research Database (Denmark)

    Latini, Simone; Winther, Kirsten Trøstrup; Olsen, Thomas

    2017-01-01

    -emitting diodes. An important first step in describing such processes is to obtain the energies of the interlayer exciton states existing at the interface. Here we present a general first-principles method to compute the electronic quasi-particle (QP) band structure and excitonic binding energies...

  11. Ultrafast electron-optical phonon scattering and quasiparticle lifetime in CVD-grown graphene.

    Science.gov (United States)

    Shang, Jingzhi; Yu, Ting; Lin, Jianyi; Gurzadyan, Gagik G

    2011-04-26

    Ultrafast quasiparticle dynamics in graphene grown by chemical vapor deposition (CVD) has been studied by UV pump/white-light probe spectroscopy. Transient differential transmission spectra of monolayer graphene are observed in the visible probe range (400-650 nm). Kinetics of the quasiparticle (i.e., low-energy single-particle excitation with renormalized energy due to electron-electron Coulomb, electron-optical phonon (e-op), and optical phonon-acoustic phonon (op-ap) interactions) was monitored with 50 fs resolution. Extending the probe range to near-infrared, we find the evolution of quasiparticle relaxation channels from monoexponential e-op scattering to double exponential decay due to e-op and op-ap scattering. Moreover, quasiparticle lifetimes of mono- and randomly stacked graphene films are obtained for the probe photon energies continuously from 1.9 to 2.3 eV. Dependence of quasiparticle decay rate on the probe energy is linear for 10-layer stacked graphene films. This is due to the dominant e-op intervalley scattering and the linear density of states in the probed electronic band. A dimensionless coupling constant W is derived, which characterizes the scattering strength of quasiparticles by lattice points in graphene.

  12. Strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2

    Science.gov (United States)

    Zhang, Wen; Liu, Yi; Wang, Xiaoying; Zhang, Yun; Xie, Donghua

    2018-03-01

    The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant band-like ones, yielding heavy quasiparticles with an effective mass about 100 times (or more) of the bare electrons. Recently, experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds, where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability. Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2. The coupling is nearly antiferromagnetic. As embedded in the ferromagnetic matrix of localized 5f moments below {T}{{C}}≈ 52 {{K}}, this coupling leads to short-range dynamic correlations of heavy quasiparticles, characterized by fluctuations of magnetic clusters. Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at {T}X≈ 28 {{K}}, which is typical for the spin-glass freezing. Thus, our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements, providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems. Project supported by the National Natural Science Foundation of China (Grant No. 11404297), the Science Challenge Project (Grant No. TZ2016004), and the Science and Technology Foundation of China Academy of Engineering Physics (Grant Nos. 2013B0301050 and 2014A0301013).

  13. Variational theory of valence fluctuations: Ground states and quasiparticle excitations of the Anderson lattice model

    Science.gov (United States)

    Brandow, B. H.

    1986-01-01

    the Kondo regime, of a significant quasiparticle contribution to the f spectral weight in the vicinity of ɛf. The present ``one-parameter'' and ``two-parameter'' versions can be viewed as lattice generalizations of the first two approximations of the (1/Nf)-expansion school, although our treatment of lattice aspects departs from strict 1/Nf methodology. The two versions have Wilson ratios ≡1 and ≠1, respectively, consistent with (1/Nf)-expansion studies of the single-impurity model, and a number of other features likewise show good correspondence with (1/Nf)-expansion results. Implications are presented for the finite-temperature behaviors of several properties, especially the specific heat and electrical resistivity. Comparison with experiment then leads to some inferences about the band structures of heavy-fermion materials. A new mechanism is presented for breakup of the coherent Fermi-liquid behavior, as temperature is increased. There are two main approximations: (a) Neglect of the ``site exclusion'' problem, i.e., within cluster-expansion terms we ignore the requirement that interacting sites must all be distinct. (b) Assumption of a low density of excited quasiparticles (those excited from the ``far'' side of the hybridization gap) limits the present treatment to very low temperatures, T<

  14. Systematic design of phononic band-gap materials and structures by topology optimization

    DEFF Research Database (Denmark)

    Sigmund, Ole; Jensen, Jakob Søndergaard

    2003-01-01

    Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used...... to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, finite structures subjected to periodic loading are optimized in order to either minimize the structural...

  15. The use of Wannier function in the calculations of band structure of covalent crystals

    International Nuclear Information System (INIS)

    Lu Dong; Yang Guang

    1985-10-01

    A variational procedure has been used to build up Wannier functions to study the energy bands of diamond, silicon and α-tin. For the case of silicon the Wannier function, density of charge and band structure are calculated self-consistently and a simple method in a non-self-consistent way has been used to compute the band structure of diamond, silicon and α-tin. The method seems to be effective to describe the electronic properties of covalent crystals. (author)

  16. The band gap variation of a two dimensional binary locally resonant structure in thermal environment

    Directory of Open Access Journals (Sweden)

    Zhen Li

    2017-01-01

    Full Text Available In this study, the numerical investigation of thermal effect on band gap dynamical characteristic for a two-dimensional binary structure composed of aluminum plate periodically filled with nitrile rubber cylinder is presented. Initially, the band gap of the binary structure variation trend with increasing temperature is studied by taking the softening effect of thermal stress into account. A breakthrough is made which found the band gap being narrower and shifting to lower frequency in thermal environment. The complete band gap which in higher frequency is more sensitive to temperature that it disappears with temperature increasing. Then some new transformed models are created by changing the height of nitrile rubber cylinder from 1mm to 7mm. Simulations show that transformed model can produce a wider band gap (either flexure or complete band gap. A proper forbidden gap of elastic wave can be utilized in thermal environment although both flexure and complete band gaps become narrower with temperature. Besides that, there is a zero-frequency flat band appearing in the first flexure band, and it becomes broader with temperature increasing. The band gap width decreases trend in thermal environment, as well as the wider band gap induced by the transformed model with higher nitrile rubber cylinder is useful for the design and application of phononic crystal structures in thermal environment.

  17. Emergence of quasiparticle Bloch states in artificial crystals crafted atom-by-atom

    Directory of Open Access Journals (Sweden)

    Jan Girovsky, Jose L. Lado, Floris E. Kalff, Eleonora Fahrenfort, Lucas J. J. M. Peters, Joaquín Fernández-Rossier, Alexander F. Otte

    2017-06-01

    Full Text Available The interaction of electrons with a periodic potential of atoms in crystalline solids gives rise to band structure. The band structure of existing materials can be measured by photoemission spectroscopy and accurately understood in terms of the tight-binding model, however not many experimental approaches exist that allow to tailor artificial crystal lattices using a bottom-up approach. The ability to engineer and study atomically crafted designer materials by scanning tunnelling microscopy and spectroscopy (STM/STS helps to understand the emergence of material properties. Here, we use atom manipulation of individual vacancies in a chlorine monolayer on Cu(100 to construct one- and two-dimensional structures of various densities and sizes. Local STS measurements reveal the emergence of quasiparticle bands, evidenced by standing Bloch waves, with tuneable dispersion. The experimental data are understood in terms of a tight-binding model combined with an additional broadening term that allows an estimation of the coupling to the underlying substrate.

  18. Quasi-particles at finite chemical potential

    International Nuclear Information System (INIS)

    Gardim, F. G.; Steffens, F. M.

    2010-01-01

    We present in this work the thermodynamic consistent quasi-particle model at finite chemical potential, to describe the Quark Gluon Plasma composed of two light quarks and gluons. The quasi-particle general solution will be discussed, and comparison with perturbative QCD and lattice data will be shown.

  19. Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd₃As₂.

    Science.gov (United States)

    Jeon, Sangjun; Zhou, Brian B; Gyenis, Andras; Feldman, Benjamin E; Kimchi, Itamar; Potter, Andrew C; Gibson, Quinn D; Cava, Robert J; Vishwanath, Ashvin; Yazdani, Ali

    2014-09-01

    Condensed-matter systems provide a rich setting to realize Dirac and Majorana fermionic excitations as well as the possibility to manipulate them for potential applications. It has recently been proposed that chiral, massless particles known as Weyl fermions can emerge in certain bulk materials or in topological insulator multilayers and give rise to unusual transport properties, such as charge pumping driven by a chiral anomaly. A pair of Weyl fermions protected by crystalline symmetry effectively forming a massless Dirac fermion has been predicted to appear as low-energy excitations in a number of materials termed three-dimensional Dirac semimetals. Here we report scanning tunnelling microscopy measurements at sub-kelvin temperatures and high magnetic fields on the II-V semiconductor Cd3As2. We probe this system down to atomic length scales, and show that defects mostly influence the valence band, consistent with the observation of ultrahigh-mobility carriers in the conduction band. By combining Landau level spectroscopy and quasiparticle interference, we distinguish a large spin-splitting of the conduction band in a magnetic field and its extended Dirac-like dispersion above the expected regime. A model band structure consistent with our experimental findings suggests that for a magnetic field applied along the axis of the Dirac points, Weyl fermions are the low-energy excitations in Cd3As2.

  20. Dynamics of correlation-frozen antinodal quasiparticles in superconducting cuprates

    Science.gov (United States)

    Cilento, Federico; Manzoni, Giulia; Sterzi, Andrea; Peli, Simone; Ronchi, Andrea; Crepaldi, Alberto; Boschini, Fabio; Cacho, Cephise; Chapman, Richard; Springate, Emma; Eisaki, Hiroshi; Greven, Martin; Berciu, Mona; Kemper, Alexander F.; Damascelli, Andrea; Capone, Massimo; Giannetti, Claudio; Parmigiani, Fulvio

    2018-01-01

    Many puzzling properties of high–critical temperature (Tc) superconducting (HTSC) copper oxides have deep roots in the nature of the antinodal quasiparticles, the elementary excitations with wave vector parallel to the Cu–O bonds. These electronic states are most affected by the onset of antiferromagnetic correlations and charge instabilities, and they host the maximum of the anisotropic superconducting gap and pseudogap. We use time-resolved extreme-ultraviolet photoemission with proper photon energy (18 eV) and time resolution (50 fs) to disclose the ultrafast dynamics of the antinodal states in a prototypical HTSC cuprate. After photoinducing a nonthermal charge redistribution within the Cu and O orbitals, we reveal a dramatic momentum-space differentiation of the transient electron dynamics. Whereas the nodal quasiparticle distribution is heated up as in a conventional metal, new quasiparticle states transiently emerge at the antinodes, similarly to what is expected for a photoexcited Mott insulator, where the frozen charges can be released by an impulsive excitation. This transient antinodal metallicity is mapped into the dynamics of the O-2p bands, thus directly demonstrating the intertwining between the low- and high-energy scales that is typical of correlated materials. Our results suggest that the correlation-driven freezing of the electrons moving along the Cu–O bonds, analogous to the Mott localization mechanism, constitutes the starting point for any model of high-Tc superconductivity and other exotic phases of HTSC cuprates. PMID:29507885

  1. Photonic band structures in one-dimensional photonic crystals containing Dirac materials

    International Nuclear Information System (INIS)

    Wang, Lin; Wang, Li-Gang

    2015-01-01

    We have investigated the band structures of one-dimensional photonic crystals (1DPCs) composed of Dirac materials and ordinary dielectric media. It is found that there exist an omnidirectional passing band and a kind of special band, which result from the interaction of the evanescent and propagating waves. Due to the interface effect and strong dispersion, the electromagnetic fields inside the special bands are strongly enhanced. It is also shown that the properties of these bands are invariant upon the lattice constant but sensitive to the resonant conditions

  2. Gamma decay and band structures in 46Ti

    International Nuclear Information System (INIS)

    Dracoulis, G.D.; Radford, D.C.; Poletti, A.R.

    1978-03-01

    The states of 46 Ti have been studied using the 43 Ca(α,nγ) reaction. The level and decay scheme of 46 Ti was deduced from γ-γ coincidence, γ-ray energy and intensity measurements. Spins are suggested on the basis of the γ-ray angular distribution, supported by relative excitation functions. The ground state band has been extended to spin 10 + , and about 20 new states are observed. Some of these can be grouped into rotational-like bands based on the 3 - state at 3.059 MeV and other excited states

  3. Qubit dephasing due to quasiparticle tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Zanker, Sebastian; Marthaler, Michael; Schoen, Gerd [Institut fuer Theoretische Festkoerperphysik, Karlsruhe Institute of Technology, D-76128 Karlsruhe (Germany)

    2015-07-01

    We study dephasing of a superconducting qubit due to quasiparticle tunneling through a Josephson junction. While qubit decay due to tunneling processes is well understood within a golden rule approximation, pure dephasing due to BCS quasiparticles gives rise to a divergent golden rule rate. We calculate qubit dephasing due to quasiparticle tunneling beyond lowest order approximation in coupling between qubit and quasiparticles. Summing up a certain class of diagrams we show that qubit dephasing due to purely longitudinal coupling to quasiparticles leads to dephasing ∝ exp(-x(t)) where x(t) ∝ t{sup 3/2} for short time scales and x(t) ∝ tlog(t) for long time scales.

  4. Quasi-particles at finite temperatures

    International Nuclear Information System (INIS)

    Narnhofer, H.; Thirring, W.; Requardt, M.

    1983-01-01

    We study the consequences of the KMS-condition on the properties of quasi-particles, assuming their existence. We establish: (i) If the correlation functions decay sufficiently, we can create them by quasi-free field operators. (ii) There are many age-operators T conjugate to H. For special forms of the dispersion law epsilon(k) of the quasi-particles there is a T commuting with the; (iii) There are many age-operators T conjugate to H. For special forms of the dispersion law epsilon(k) of the quasi-particles there is a T commuting with the number of quasi-particles and its time-monotonicity describes how the quasi-particles travel to infinity. (orig.)

  5. Universal spectral signatures in pnictides and cuprates: the role of quasiparticle-pair coupling.

    Science.gov (United States)

    Sacks, William; Mauger, Alain; Noat, Yves

    2017-11-08

    Understanding the physical properties of a large variety of high-T c superconductors (SC), the cuprate family as well as the more recent iron-based superconductors, is still a major challenge. In particular, these materials exhibit the 'peak-dip-hump' structure in the quasiparticle density of states (DOS). The origin of this structure is explained within our pair-pair interaction (PPI) model: The non-superconducting state consists of incoherent pairs, a 'Cooper-pair glass' which, due to the PPI, undergoes a Bose-like condensation below T c to the coherent SC state. We derive the equations of motion for the quasiparticle operators showing that the DOS 'peak-dip-hump' is caused by the coupling between quasiparticles and excited pair states, or 'super-quasiparticles'. The renormalized SC gap function becomes energy-dependent and non retarded, reproducing accurately the experimental spectra of both pnictides and cuprates, despite the large difference in gap value.

  6. Optical verification of the valence band structure of cadmium arsenide

    NARCIS (Netherlands)

    Gelten, M.J.; Es, van C.M.; Blom, F.A.P.; Jongeneelen, J.W.F.

    1980-01-01

    Optical absorption measurements were performed on thin single crystalline samples of Cd3As2 at temperatures of 300 K and 10 K. At low temperature the interband absorption coefficient shows clearly two steps due to direct transitions from the heavy hole and light hole valence bands to the conduction

  7. Structure research of L-band travelling-wave buncher

    International Nuclear Information System (INIS)

    Zhou Wenzhen; Zhang Xiangyang; Ding Shuling

    1996-01-01

    The authors introduce design and tuning of two kinds of the buncher of the L-band high current injector of China Institute of Atomic Energy. Characteristics of the few cavities buncher is shown and the effects of the two modes of the buncher in high current injector are given

  8. Collective motions and band structures in A = 60 to 80, even--even nuclei

    International Nuclear Information System (INIS)

    Hamilton, J.H.; Robinson, R.L.; Ramayya, A.V.

    1978-01-01

    Evidence for and the theoretical understanding of the richness of the collective band structures as illustrated by at least seven bands seen in levels of 68 Ge, 74 Se are reviewed. The experimental data on even-even nuclei in the A = 60 to 80 region have now revealed a wide variety of collective bands with different structures. The even parity yrast cascades alone are seen to involve multiple collective structures. In addition to the ground-state bands, strong evidence is presented for both neutron and proton rotation-aligned bands built on the same orbital, (g 9 / 2 ) 2 , in one nucleus. Several other nuclei also show the crossing of RAL bands around the 8 + level in this region. Evidence continues to be strong experimentally and supported theoretically that there is some type of shape transition and shape coexistence occurring now both in the Ge and Se isotopes around N = 40. Negative parity bands with odd and even spins with very collective nature are seen in several nuclei to high spin. These bands seem best understood in the RAL model. Very collective bands with ΔI = 1, extending from 2 + to 9 + are seen with no rotation-alignment. The purity of these bands and their persistence to such high spin establish them as an independent collective mode which is best described as a gamma-type vibration band in a deformed nucleus. In addition to all of the above bands, new bands are seen in 76 Kr and 74 Se. The nature of these bands is not presently known. 56 references

  9. Band crossings in mercury nuclei: effect of occupation of i13/2 neutron orbits

    International Nuclear Information System (INIS)

    Khadkikar, S.B.; Praharaj, C.R.

    1984-04-01

    The K=0 + ground band and two rotation-aligned bands (K=1 + or K2 + two quasi-particle band and K=2 + four quasi-particle band) are studied in 198 Hg, 194 Hg and 190 Hg by angular momentum projection from Hartree-Fock and particle-hole intrinsic states. There is a first anomaly in these three nuclei around 8(h/2π) due to the crossing of the ground band and the two quasi-particle band. Because of the nature of occupation of i13/2 orbitals the four quasi-particle band is too highlying in 198 Hg and does not cross the two quasi-particle bands, while such a second crossing occurs in 194 Hg and 190 Hg near 20 (h/2π). (author)

  10. Engineering the electronic band structures of novel cubic structured germanium monochalcogenides for thermoelectric applications

    Science.gov (United States)

    Ul Haq, Bakhtiar; AlFaify, S.; Ahmed, R.; Butt, Faheem K.; Laref, A.; Goumri-Said, Souraya; Tahir, S. A.

    2018-05-01

    Germanium mono-chalcogenides have received considerable attention for being a promising replacement for the relatively toxic and expensive chalcogenides in renewable and sustainable energy applications. In this paper, we explore the potential of the recently discovered novel cubic structured (π-phase) GeS and GeSe for thermoelectric applications in the framework of density functional theory coupled with Boltzmann transport theory. To examine the modifications in their physical properties, the across composition alloying of π-GeS and π-GeSe (such as π-GeS1-xSex for x =0, 0.25, 0.50, 0.75, and 1) has been performed that has shown important effects on the electronic band structures and effective masses of charge carriers. An increase in Se composition in π-GeS1-xSex has induced a downward shift in their conduction bands, resulting in the narrowing of their energy band gaps. The thermoelectric coefficients of π-GeS1-xSex have been accordingly influenced by the evolution of the electronic band structures and effective masses of charge carriers. π-GeS1-xSex features sufficiently larger values of Seebeck coefficients, power factors and figures of merit (ZTs), which experience further improvement with an increase in temperature, revealing their potential for high-temperature applications. The calculated results show that ZT values equivalent to unity can be achieved for π-GeS1-xSex at appropriate n-type doping levels. Our calculations for the formation enthalpies indicate that a π-GeS1-xSex alloying system is energetically stable and could be synthesized experimentally. These intriguing characteristics make π-GeS1-xSex a promising candidate for futuristic thermoelectric applications in energy harvesting devices.

  11. Majorana quasiparticles in semiconducting carbon nanotubes

    Science.gov (United States)

    Marganska, Magdalena; Milz, Lars; Izumida, Wataru; Strunk, Christoph; Grifoni, Milena

    2018-02-01

    Engineering effective p -wave superconductors hosting Majorana quasiparticles (MQPs) is nowadays of particular interest, also in view of the possible utilization of MQPs in fault-tolerant topological quantum computation. In quasi-one-dimensional systems, the parameter space for topological superconductivity is significantly reduced by the coupling between transverse modes. Together with the requirement of achieving the topological phase under experimentally feasible conditions, this strongly restricts in practice the choice of systems which can host MQPs. Here, we demonstrate that semiconducting carbon nanotubes (CNTs) in proximity with ultrathin s -wave superconductors, e.g., exfoliated NbSe2, satisfy these needs. By precise numerical tight-binding calculations in the real space, we show the emergence of localized zero-energy states at the CNT ends above a critical value of the applied magnetic field, of which we show the spatial evolution. Knowing the microscopic wave functions, we unequivocally demonstrate the Majorana nature of the localized states. An effective four-band model in the k -space, with parameters determined from the numerical spectrum, is used to calculate the topological phase diagram and its phase boundaries in analytic form. Finally, the impact of symmetry breaking contributions, like disorder and an axial component of the magnetic field, is investigated.

  12. The decay from the two-quasiparticle regime in even-even deformed rare earth nuclei

    International Nuclear Information System (INIS)

    Henriques, A.; Thorstensen, T.F.; Hammaren, E.

    1983-06-01

    A bump at 1 MeV has been identified in coincidence gamma-ray spectra from the ( 3 He, 4 He) reaction in deformed rare earth nuclei. Particle/gamma-ray angular correlation indicates a dipole character. It is suggested that this bump corresponds to transitions from two-quasiparticle states to the ground state band

  13. Effect of pressure on the structural properties and electronic band structure of GaSe

    Energy Technology Data Exchange (ETDEWEB)

    Schwarz, U.; Olguin, D.; Syassen, K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Cantarero, A. [Department of Materials Sciences, University of Valencia, 46000 Burjasot (Spain); Hanfland, M. [European Synchrotron Radiation Facility, BP 220, 38043 Grenoble (France)

    2007-01-15

    The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the {epsilon}-GaSe to a disordered NaCl-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered {epsilon}-phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga-Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga-Ga and Se-Se bond lengths which were not accessible to a direct experimental determination yet. Based on the optimized structural parameters, we report calculations of band gap changes of {epsilon}-GaSe under pressure. The optical response and electronic band structure of the metallic high-pressure phase of GaSe are discussed briefly. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. 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

    is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi...... of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.......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...

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

    Energy Technology Data Exchange (ETDEWEB)

    Stephenson, C. A., E-mail: cstephe3@nd.edu; Stillwell, R. A.; Wistey, M. A. [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); O' Brien, W. A. [Rigetti Quantum Computing, 775 Heinz Avenue, Berkeley, California 94710 (United States); Penninger, M. W. [Honeywell UOP, Des Plaines, Illinois 60016 (United States); Schneider, W. F. [Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Gillett-Kunnath, M. [Department of Chemistry, Syracuse University, Syracuse, New York 13244 (United States); Zajicek, J. [Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Yu, K. M. [Department of Physics and Materials Science, City University of Hong Kong, Hong Kong (China); Kudrawiec, R. [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

    2016-08-07

    Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge{sub 1−x}C{sub x} (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 Ge{sub 0.998}C{sub 0.002} shows a bandgap reduction supporting these results. Growth of Ge{sub 0.998}C{sub 0.002} 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.

  16. Fine structure of the amide i band in acetanilide

    Science.gov (United States)

    Careri, G.; Gratton, E.; Shyamsunder, E.

    1988-05-01

    Their absorption spectrum of both single crystals and powdered samples of acetanilide (a model system for proteins) has been studied in the amide i region, where a narrow band has been identified as a highly trapped soliton state. The powder-sample spectra have been decomposed using four Lorentzian bands. A strong temperature dependence has been found for the intensity of two of the subbands, which also show a complementary behavior. Polarization studies performed on thin crystals have shown that the subbands have the same polarization. Low-temperature spectra of partially deuterated samples show the presence of the subbands at the same absorption frequencies found using the fitting procedure in the spectra of nondeuterated samples. The soliton model currently proposed to explain the origin of the anomalous amide i component at 1650 cm-1 still holds, but some modification of the model is required to account for the new features revealed by this study.

  17. Band structure in 83Rb from lifetime measurements

    International Nuclear Information System (INIS)

    Ganguly, S.; Banerjee, P.; Ray, I.; Kshetri, R.; Bhattacharya, S.; Saha-Sarkar, M.; Goswami, A.; Muralithar, S.; Singh, R.P.; Kumar, R.; Bhowmik, R.K.

    2006-01-01

    Excited states of 83 Rb, populated in the 76 Ge( 11 B,-bar 4nγ) reaction at a beam energy of 50 MeV, have been studied. The unfavoured signature partner (α=-1/2) of the πg 9/2 yrast band is proposed up to an excitation energy of 6669.4 keV and spin (31/2 + ). Lifetimes have been estimated for three states belonging to the favoured α=+1/2 band. The B(E2) values deduced from these lifetimes indicate a moderate quadrupole deformation of β 2 =0.20. Theoretical calculations within the framework of the particle-rotor-model suggest that low energy states before the onset of the νg 9/2 alignment at a rotational frequency of ∼0.5 MeV are prolate while those above this frequency have an oblate shape. The excited ΔI=1 band has been extended up to 5422.7 keV and spin 25/2 - . The B(M1) rates derived from the measured lifetimes decrease with spin. The results are in general agreement with an earlier TAC calculation, suggesting the interpretation of these states as arising from magnetic rotation

  18. Band structure in {sup 83}Rb from lifetime measurements

    Energy Technology Data Exchange (ETDEWEB)

    Ganguly, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Banerjee, P. [Saha Institute of Nuclear Physics, Kolkata 700064 (India)]. E-mail: polash.banerjee@saha.ac.in; Ray, I. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Kshetri, R. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Bhattacharya, S. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Saha-Sarkar, M. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Goswami, A. [Saha Institute of Nuclear Physics, Kolkata 700064 (India); Muralithar, S. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India); Singh, R.P. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India); Kumar, R. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India); Bhowmik, R.K. [Nuclear Science Centre, Post Box 10502, New Delhi 110067 (India)

    2006-03-20

    Excited states of {sup 83}Rb, populated in the {sup 76}Ge({sup 11}B,-bar 4n{gamma}) reaction at a beam energy of 50 MeV, have been studied. The unfavoured signature partner ({alpha}=-1/2) of the {pi}g{sub 9/2} yrast band is proposed up to an excitation energy of 6669.4 keV and spin (31/2{sup +}). Lifetimes have been estimated for three states belonging to the favoured {alpha}=+1/2 band. The B(E2) values deduced from these lifetimes indicate a moderate quadrupole deformation of {beta}{sub 2}=0.20. Theoretical calculations within the framework of the particle-rotor-model suggest that low energy states before the onset of the {nu}g{sub 9/2} alignment at a rotational frequency of {approx}0.5 MeV are prolate while those above this frequency have an oblate shape. The excited {delta}I=1 band has been extended up to 5422.7 keV and spin 25/2{sup -}. The B(M1) rates derived from the measured lifetimes decrease with spin. The results are in general agreement with an earlier TAC calculation, suggesting the interpretation of these states as arising from magnetic rotation.

  19. Quasiparticle energy distribution and relaxation times in a tunnel-injected superconductor

    International Nuclear Information System (INIS)

    Kirtley, J.R.; Kent, D.S.; Langenberg, D.N.; Kaplan, S.B.; Chang, J.; Yang, C.

    1980-01-01

    Experiments are reported in which a nonequilibrium quasiparticle distribution was created in a dirty Al film by tunnel injection and probed using a second tunnel junction. The distribution was found to have the form of a quasithermal distribution characterized by an effective temperature greater than the ambient bath temperature and dependent on injection level, plus small sharp structures which originate in structures in the injected quasiparticle distribution due to gap-edge peaks in the quasiparticle density of states. A systematic theoretical analysis of these structures correctly predicts their shapes and relative amplitudes. The amplitudes show directly the presence of branch imbalance in the nonequilibrium quasiparticle distribution. Using the theoretical model, inelastic quasiparticle relaxation and elastic branch mixing times, as functions of energy and temperature, are extracted from the experimental data without need for phonon-trapping corrections. The qualitative and quantitative behavior of these times is in reasonable accord with theoretical expectations and the results of other experiments. Experiments of the type reported here are shown to provide a kind of spectroscopy of tunnel-injection and quasiparticle-relaxation processes in superconductors

  20. 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.

  1. Theoretical interpretation of the nuclear structure of 88Se within the ACM and the QPM models.

    Science.gov (United States)

    Gratchev, I. N.; Thiamova, G.; Alexa, P.; Simpson, G. S.; Ramdhane, M.

    2018-02-01

    The four-parameter algebraic collective model (ACM) Hamiltonian is used to describe the nuclear structure of 88Se. It is shown that the ACM is capable of providing a reasonable description of the excitation energies and relative positions of the ground-state band and γ band. The most probable interpretation of the nuclear structure of 88Se is that of a transitional nucleus. The Quasiparticle-plus-Phonon Model (QPM) was also applied to describe the nuclear motion in 88Se. Preliminarily calculations show that the collectivity of second excited state {2}2+ is weak and that this state contains a strong two-quasiparticle component.

  2. Microscopic description of magnetized plasma: quasiparticle concept

    International Nuclear Information System (INIS)

    Sosenko, P.P.; Decyk, V.K.

    1993-01-01

    A quasiparticle concept is developed systematically, from first principles, within the context of microscopic description of magnetized plasma. It is argued that the zeroth velocity-gyroangle harmonic of the microscopic particle distribution function under the gyrokinetic change of variables can be taken as a microscopic quasi-particle density in a reduced phase space. The nature of quasiparticles is discussed and equations of their motion are derived within both exact and reduced microscopic descriptions. The reduced one employs explicitly the separation of interesting time scales. (orig.)

  3. 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.

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

    International Nuclear Information System (INIS)

    Kozyukhin, S.; Golovchak, R.; Kovalskiy, A.; Shpotyuk, O.; Jain, H.

    2011-01-01

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As x Se 100−x , As x S 100−x , Ge x Se 100−x and Ge x S 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.

  5. 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.

  6. Compact electromagnetic bandgap structures for notch band in ultra-wideband applications.

    Science.gov (United States)

    Rotaru, Mihai; Sykulski, Jan

    2010-01-01

    This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15-5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied.

  7. High gradient test of X-band accelerating structure at GLCTA

    International Nuclear Information System (INIS)

    Watanabe, K.; Higo, T.; Hayano, H.; Terunuma, N.; Saeki, T.; Kudo, N.; Sanuki, T.; Seuhara, T.

    2004-01-01

    GLCTA (Global Linear Collider Test Accelerator) is the high power test facility for X-band acceleration. We have installed an X-band 60cm structure in April 2004 and have been processing it for more than 3 months. Now it is under test on long-term operation. We report here the installation process and high power test result to date. (author)

  8. Structure of the lowest excited 0/sup +/ rotational band of /sup 16/O

    Energy Technology Data Exchange (ETDEWEB)

    Ikebata, Yasuhiko; Suekane, Shota

    1983-10-01

    The structure of the lowest excited 0/sup +/ rotational band is investigated by using the extended Nilsson model wave functions with angular momentum projection and the B1 interaction, two-body LS-force of the Skyrme type and the Coulomb interaction. The results obtained show good agreement with energy interval in this band.

  9. Electronic band structure study of colossal magnetoresistance in Tl 2Mn 2O 7

    Science.gov (United States)

    Seo, D.-K.; Whangbo, M.-H.; Subramanian, M. A.

    1997-02-01

    The electronic structure of Tl 2Mn 2O 7 was examined by performing tight binding band calculations. The overlap between the Mn t 2g- and Tl 6 s-block bands results in a partial filling of the Tl 6 s-block bands. The associated Fermi surface consists of 12 cigar-shape electron pockets with each electron pocket about {1}/{1000} of the first Brillouin zone in size. The Tl 6 s-block bands have orbital contributions from the Mn atoms, and the carrier density is very low. These are important for the occurrence of a colossal magnetoresistance in Tl 2Mn 2O 7.

  10. Three band crossings in the yrast structure of 162Hf

    International Nuclear Information System (INIS)

    Bingham, C.R.; Riedinger, L.L.; Courtney, L.H.

    1988-01-01

    The yrast sequence of 162 Hf has been observed up to a level tentatively assigned as 38 + and reveals a continuing rotational character up to that spin. Sharp backbends at rotational frequencies of 0.27 and 0.42 MeV/ℎ are attributed to isub(13/2) neutron and hsub(11/2) proton alignments, respectively. A gradual increase in the aligned angular momentum of the yrast levels between these two sharp backbends is attributed to the rotational alignment of a pair of negative parity quasineutrons (mostly hsub(9/2) in character). The interpretation of this effect is supported by the failure of the negative parity bands, which already contain this aligned hsub(9/2) neutron, to gain alignment in the same rotational frequency range. While the alignment of the hsub(9/2) quasineutrons has been predicted in the cranked shell model to occur in the rare-earth region with a large interaction strength, this represents the first clear observation of such a band crossing. (author)

  11. Phonon-Mediated Quasiparticle Poisoning of Superconducting Microwave Resonators

    OpenAIRE

    Patel, U.; Pechenezhskiy, Ivan V.; Plourde, B. L. T.; Vavilov, M. G.; McDermott, R.

    2016-01-01

    Nonequilibrium quasiparticles represent a significant source of decoherence in superconducting quantum circuits. Here we investigate the mechanism of quasiparticle poisoning in devices subjected to local quasiparticle injection. We find that quasiparticle poisoning is dominated by the propagation of pair-breaking phonons across the chip. We characterize the energy dependence of the timescale for quasiparticle poisoning. Finally, we observe that incorporation of extensive normal metal quasipar...

  12. Efficient many-body calculations for two-dimensional materials using exact limits for the screened potential: Band gaps of MoS2, h-BN, and phosphorene

    DEFF Research Database (Denmark)

    Rasmussen, Filip Anselm; Schmidt, Per Simmendefeldt; Winther, Kirsten Trøstrup

    2016-01-01

    Calculating the quasiparticle (QP) band structure of two-dimensional (2D) materials within the GW self-energy approximation has proven to be a rather demanding computational task. The main reason is the strong q dependence of the 2D dielectric function around q = 0 that calls for a much denser...

  13. Hybridization in Kondo lattice heavy fermions via quasiparticle scattering spectroscopy (QPS)

    Science.gov (United States)

    Narasiwodeyar, Sanjay; Dwyer, Matt; Greene, Laura; Park, Wan Kyu; Bauer, Eric; Tobash, Paul; Baumbach, Ryan; Ronning, Filip; Sarrao, John; Thompson, Joe; Canfield, Paul

    2014-03-01

    Band renormalization in a Kondo lattice via hybridization of the conduction band with localized states has been a hot topic over the last several years. In part, this has to do with recently reignited interest in the hidden order problem in URu2Si2. Despite recent developments regarding the electronic structure in this compound, it remains to be resolved whether the hidden order phase transition is related to the opening of a hybridization gap. Our quasiparticle scattering spectroscopy (QPS) has shown they are not related directly. This can be understood naturally since in principle band renormalization does not involve symmetry breaking. To deepen our understanding, we extend to other Kondo lattice compounds. For instance, when applied to YbAl3, a vegetable heavy-fermion system, QPS reveals conductance signatures for hybridization in a Kondo lattice such as asymmetric Fano background along with characteristic energy scales. Presenting new results on these materials, we will discuss a broader picture. The work at UIUC is supported by the NSF DMR 12-06766, the work at LANL is carried out under the auspices of the U.S. DOE, Office of Science, and the work done at Ames Lab. was supported under Contract No. DE-AC02-07CH11358.

  14. Cell and band structures in cold rolled polycrystalline copper

    DEFF Research Database (Denmark)

    Ananthan, V.S.; Leffers, Torben; Hansen, Niels

    1991-01-01

    dislocation walls (DDWs) and cells develop during the initial stages of cold rolling. Grains having a high density of DDWs are described as high wall density (HWD) structures, and grains having a low density of DDWs are described as low wall density (LWD) structures. These structures are characterised by cell...

  15. Angle-resolved photoemission spectroscopy of band tails in lightly doped cuprates

    OpenAIRE

    Alexandrov, A. S.; Reynolds, K.

    2007-01-01

    We amend ab initio strongly-correlated band structures by taking into account the band-tailing phenomenon in doped charge-transfer Mott-Hubbard insulators. We show that the photoemission from band tails accounts for sharp "quasi-particle" peaks, rapid loss of their intensities in some directions of the Brillouin zone ("Fermi-arcs") and high-energy "waterfall" anomalies as a consequence of matrix-element effects of disorder-localised states in the charge-transfer gap of doped cuprates.

  16. Quasiparticle and excitonic gaps of one-dimensional carbon chains.

    Science.gov (United States)

    Mostaani, E; Monserrat, B; Drummond, N D; Lambert, C J

    2016-06-01

    We report diffusion quantum Monte Carlo (DMC) calculations of the quasiparticle and excitonic gaps of hydrogen-terminated oligoynes and extended polyyne. The electronic gaps are found to be very sensitive to the atomic structure in these systems. We have therefore optimised the geometry of polyyne by directly minimising the DMC energy with respect to the lattice constant and the Peierls-induced carbon-carbon bond-length alternation. We find the bond-length alternation of polyyne to be 0.136(2) Å and the excitonic and quasiparticle gaps to be 3.30(7) and 3.4(1) eV, respectively. The DMC zone-centre longitudinal optical phonon frequency of polyyne is 2084(5) cm(-1), which is consistent with Raman spectroscopic measurements for large oligoynes.

  17. Quasiparticle spin resonance and coherence in superconducting aluminium.

    Science.gov (United States)

    Quay, C H L; Weideneder, M; Chiffaudel, Y; Strunk, C; Aprili, M

    2015-10-26

    Conventional superconductors were long thought to be spin inert; however, there is now increasing interest in both (the manipulation of) the internal spin structure of the ground-state condensate, as well as recently observed long-lived, spin-polarized excitations (quasiparticles). We demonstrate spin resonance in the quasiparticle population of a mesoscopic superconductor (aluminium) using novel on-chip microwave detection techniques. The spin decoherence time obtained (∼100 ps), and its dependence on the sample thickness are consistent with Elliott-Yafet spin-orbit scattering as the main decoherence mechanism. The striking divergence between the spin coherence time and the previously measured spin imbalance relaxation time (∼10 ns) suggests that the latter is limited instead by inelastic processes. This work stakes out new ground for the nascent field of spin-based electronics with superconductors or superconducting spintronics.

  18. Quasiparticle features and level statistics of odd-odd nucleus

    International Nuclear Information System (INIS)

    Cheng Nanpu; Zheng Renrong; Zhu Shunquan

    2001-01-01

    The energy levels of the odd-odd nucleus 84 Y are calculated by using the axially symmetric rotor plus quasiparticles model. The two standard statistical tests of Random-Matrix Theory such as the distribution function p(s) of the nearest-neighbor level spacings (NNS) and the spectral rigidity Δ 3 are used to explore the statistical properties of the energy levels. By analyzing the properties of p(s) and Δ 3 under various conditions, the authors find that the quasiparticle features mainly affect the statistical properties of the odd-odd nucleus 84 Y through the recoil term and the Coriolis force in this theoretical mode, and that the chaotic degree of the energy levels decreases with the decreasing of the Fermi energy and the energy-gap parameters. The effect of the recoil term is small while the Coriolis force plays a major role in the spectral structure of 84 Y

  19. Band structure and orbital character of monolayer MoS2 with eleven-band tight-binding model

    Science.gov (United States)

    Shahriari, Majid; Ghalambor Dezfuli, Abdolmohammad; Sabaeian, Mohammad

    2018-02-01

    In this paper, based on a tight-binding (TB) model, first we present the calculations of eigenvalues as band structure and then present the eigenvectors as probability amplitude for finding electron in atomic orbitals for monolayer MoS2 in the first Brillouin zone. In these calculations we are considering hopping processes between the nearest-neighbor Mo-S, the next nearest-neighbor in-plan Mo-Mo, and the next nearest-neighbor in-plan and out-of-plan S-S atoms in a three-atom based unit cell of two-dimensional rhombic MoS2. The hopping integrals have been solved in terms of Slater-Koster and crystal field parameters. These parameters are calculated by comparing TB model with the density function theory (DFT) in the high-symmetry k-points (i.e. the K- and Γ-points). In our TB model all the 4d Mo orbitals and the 3p S orbitals are considered and detailed analysis of the orbital character of each energy level at the main high-symmetry points of the Brillouin zone is described. In comparison with DFT calculations, our results of TB model show a very good agreement for bands near the Fermi level. However for other bands which are far from the Fermi level, some discrepancies between our TB model and DFT calculations are observed. Upon the accuracy of Slater-Koster and crystal field parameters, on the contrary of DFT, our model provide enough accuracy to calculate all allowed transitions between energy bands that are very crucial for investigating the linear and nonlinear optical properties of monolayer MoS2.

  20. 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

    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/G...... wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.......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 In......N/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...

  1. Energetic band structure of Zn3P2 crystals

    Science.gov (United States)

    Stamov, I. G.; Syrbu, N. N.; Dorogan, A. V.

    2013-01-01

    Optical functions n, k, ε1, ε2 and d2ε2/dE2 have been determined from experimental reflection spectra in the region of 1-10 eV. The revealed electronic transitions are localized in the Brillouin zone. The magnitude of valence band splitting caused by the spin-orbital interaction ΔSO is lower than the splitting caused by the crystal field ΔCR in the center of Brillouin zone and L and X points. The switching effects are investigated in Zn3P2 crystals. The characteristics of experimental samples with electric switching, adjustable resistors, and time relays based on Zn3P2 are presented.

  2. Design and Analysis of a Triple Stop-band Filter Using Ratioed Periodical Defected Microstrip Structure

    Science.gov (United States)

    Jiang, Tao; Wang, Yanyan; Li, Yingsong

    2017-07-01

    In this paper, a triple stop-band filter with a ratioed periodical defected microstrip structure is proposed for wireless communication applications. The proposed ratioed periodical defected microstrip structures are spiral slots, which are embedded into a 50 Ω microstrip line to obtain multiple stop-bands. The performance of the proposed triple stop-band filter is investigated numerically and experimentally. Moreover, the equivalent circuit model of the proposed filter is also established and discussed. The results are given to verify that the proposed triple stop-band filter has three stop bands at 3.3 GHz, 5.2 GHz, 6.8 GHz to reject the unwanted signals, which is promising for integrating into UWB communication systems to efficiently prevent the potential interferences from unexpected narrowband signals such as WiMAX, WLAN and RFID communication systems.

  3. Measuring the band structures of periodic beams using the wave superposition method

    Science.gov (United States)

    Junyi, L.; Ruffini, V.; Balint, D.

    2016-11-01

    Phononic crystals and elastic metamaterials are artificially engineered periodic structures that have several interesting properties, such as negative effective stiffness in certain frequency ranges. An interesting property of phononic crystals and elastic metamaterials is the presence of band gaps, which are bands of frequencies where elastic waves cannot propagate. The presence of band gaps gives this class of materials the potential to be used as vibration isolators. In many studies, the band structures were used to evaluate the band gaps. The presence of band gaps in a finite structure is commonly validated by measuring the frequency response as there are no direct methods of measuring the band structures. In this study, an experiment was conducted to determine the band structure of one dimension phononic crystals with two wave modes, such as a bi-material beam, using the frequency response at only 6 points to validate the wave superposition method (WSM) introduced in a previous study. A bi-material beam and an aluminium beam with varying geometry were studied. The experiment was performed by hanging the beams freely, exciting one end of the beams, and measuring the acceleration at consecutive unit cells. The measured transfer function of the beams agrees with the analytical solutions but minor discrepancies. The band structure was then determined using WSM and the band structure of one set of the waves was found to agree well with the analytical solutions. The measurements taken for the other set of waves, which are the evanescent waves in the bi-material beams, were inaccurate and noisy. The transfer functions at additional points of one of the beams were calculated from the measured band structure using WSM. The calculated transfer function agrees with the measured results except at the frequencies where the band structure was inaccurate. Lastly, a study of the potential sources of errors was also conducted using finite element modelling and the errors in

  4. Tailoring band structure and band filling in a simple cubic (IV, III)-VI superconductor

    Science.gov (United States)

    Kriener, M.; Kamitani, M.; Koretsune, T.; Arita, R.; Taguchi, Y.; Tokura, Y.

    2018-04-01

    Superconductivity and its underlying mechanisms are one of the most active research fields in condensed-matter physics. An important question is how to enhance the transition temperature Tc of a superconductor. In this respect, the possibly positive role of valence-skipping elements in the pairing mechanism has been attracting considerable interest. Here we follow this pathway and successfully enhance Tc up to almost 6 K in the simple chalcogenide SnTe known as a topological crystalline insulator by doping the valence-skipping element In substitutionally for the Sn site and codoping Se for the Te site. A high-pressure synthesis method enabled us to form single-phase solid solutions Sn1 -xInxTe1 -ySey over a wide composition range while keeping the cubic structure necessary for the superconductivity. Our experimental results are supported by density-functional theory calculations which suggest that even higher Tc values would be possible if the required doping range was experimentally accessible.

  5. High Power Test of an X-Band Slotted-IRIS Accelerator Structure at NLCTA

    International Nuclear Information System (INIS)

    Doebert, S.; Fandos, R.; Grudiev, A.; Heikkinen, S.; Rodriquez, J.A.; Taborelli, M.; Wuensch, W.; Adolphsen, Chris E.; Laurent, L.

    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

  6. γ-transitions from neutron resonances and many-quasiparticle configurations

    International Nuclear Information System (INIS)

    Soloviev, V.G.

    1991-01-01

    One should answer the question posed in 1972: Are there large many-quasiparticle components in the wave functions of highly excited low-spin states and, in particular, of neutron resonances? With increasing excitation energy the structure of states becomes more complex; the contribution of few-quasiparticle components to wave function normalization decreases exponentially and for the neutron resonances of heavy nuclei it equals 10 -6 . It is obvious that the wave function of neutron resonances contain many thousands of various quasiparticle components. Two extreme cases are possible. In the first case all the components are small and distributed according to statistical laws. In the second case among many components there is one or a few large many-quasiparticle components. There are many-quasiparticle isomers with high spins whose large life-time is due to the absence of few-quasiparticle components. This indicates a small fragmentation of these states. Low-spin states are fragmented more strongly than high-spin ones. What experiments are to be performed to answer the question about the existence are to be performed to answer the question about the existence of many-quasiparticle components of the wave functions of neutron resonances? It seems that the most straight way for observing large many-quasiparticle components is many-nucleon transfer reactions. However, in this way one faces great difficulties. The author thinks it to be more convenient to study γ transitions from neutron resonances to the states with energies by 1-2 MeV less than the energies of neutron resonances

  7. Converged G W quasiparticle energies for transition metal oxide perovskites

    Science.gov (United States)

    Ergönenc, Zeynep; Kim, Bongjae; Liu, Peitao; Kresse, Georg; Franchini, Cesare

    2018-02-01

    The ab initio calculation of quasiparticle (QP) energies is a technically and computationally challenging problem. In condensed matter physics, the most widely used approach to determine QP energies is the G W approximation. Although the G W method has been widely applied to many typical semiconductors and insulators, its application to more complex compounds such as transition metal oxide perovskites has been comparatively rare, and its proper use is not well established from a technical point of view. In this work, we have applied the single-shot G0W0 method to a representative set of transition metal oxide perovskites including 3 d (SrTiO3, LaScO3, SrMnO3, LaTiO3, LaVO3, LaCrO3, LaMnO3, and LaFeO3), 4 d (SrZrO3, SrTcO3, and Ca2RuO4 ), and 5 d (SrHfO3, KTaO3, and NaOsO3) compounds with different electronic configurations, magnetic orderings, structural characteristics, and band gaps ranging from 0.1 to 6.1 eV. We discuss the proper procedure to obtain well-converged QP energies and accurate band gaps within single-shot G0W0 by comparing the conventional approach based on an incremental variation of a specific set of parameters (number of bands, energy cutoff for the plane-wave expansion and number of k points) and the basis-set extrapolation scheme [J. Klimeš et al., Phys. Rev. B 90, 075125 (2014), 10.1103/PhysRevB.90.075125]. Although the conventional scheme is not supported by a formal proof of convergence, for most cases it delivers QP energies in reasonably good agreement with those obtained by the basis-set correction procedure and it is by construction more useful for calculating band structures. In addition, we have inspected the difference between the adoption of norm-conserving and ultrasoft potentials in G W calculations and found that the norm violation for the d shell can lead to less accurate results in particular for charge-transfer systems and late transition metals. A minimal statistical analysis indicates that the correlation of the G W data

  8. Band structure of Mgsub(x)Znsub(1-x)Te alloys

    International Nuclear Information System (INIS)

    Laugier, A.; Montegu, B.; Barbier, D.; Chevallier, J.; Guillaume, J.C.; Somogyi, K.

    1980-01-01

    The band structure of Mgsub(x)Znsub(1-x)Te alloys is studied using a double beam wavelength modulated system in first derivative mode. Modulated reflectivity measurements are made from 82 to 300 K within spectral range 2500 to 5400 A. Structures corresponding to the E 0 , E 0 + Δ 0 , E 1 , E 1 + Δ 1 , e 1 and e 1 + Δ 1 critical points are indexed on the basis of existing band calculations for ZnTe. (author)

  9. Complete flexural vibration band gaps in membrane-like lattice structures

    International Nuclear Information System (INIS)

    Yu Dianlong; Liu Yaozong; Qiu Jing; Wang Gang; Zhao Honggang

    2006-01-01

    The propagation of flexural vibration in the periodical membrane-like lattice structure is studied. The band structure calculated with the plane wave expansion method indicates the existence of complete gaps. The frequency response function of a finite periodic structure is simulated with finite element method. Frequency ranges with vibration attenuation are in good agreement with the gaps found in the band structure. Much larger attenuations are found in the complete gaps comparing to those directional ones. The existence of complete flexural vibration gaps in such a lattice structure provides a new idea for vibration control of thin plates

  10. Multi-cavity locally resonant structure with the low frequency and broad band-gaps

    Directory of Open Access Journals (Sweden)

    Jiulong Jiang

    2016-11-01

    Full Text Available A multi-cavity periodic structure with the characteristic of local resonance was proposed in the paper. The low frequency band-gap structure was comparatively analyzed by the finite element method (FEM and electric circuit analogy (ECA. Low frequency band-gap can be opened through the dual influence of the coupling’s resonance in the cavity and the interaction among the couplings between structures. Finally, the influence of the structural factors on the band-gap was analyzed. The results show that the structure, which is divided into three parts equally, has a broader effective band-gap below the frequency of 200 Hz. It is also proved that reducing the interval between unit structures can increase the intensity of the couplings among the structures. And in this way, the width of band-gap would be expanded significantly. Through the parameters adjustment, the structure enjoys a satisfied sound insulation effect below the frequency of 500Hz. In the area of low frequency noise reduction, the structure has a lot of potential applications.

  11. On the structure of collective bands in 78Kr

    International Nuclear Information System (INIS)

    Hellmeister, H.P.

    1980-01-01

    Using 16 O, 19 F, and 12 C induced reactions high spin states in 78 Kr were excited. The targets consisted of 65 Cu, 69 Ni, and 68 Zn. On the base of gamma spectroscopic methods as γγ-coincidences, angular distributions and excitation functions a level scheme of 78 Kr is proposed. Four bands could be identified, which decay mostly by stretched E2-transitions. From recoil distance Doppler shift as well as Doppler shift attenuation measurements lifetimes of about 20 states were measured. The β-decay of the 103 keV isomeric state and the ground state in 78 Rb was observed and the half-lifes determined. Altogether a very good agreement of the level scheme and the E2- and E1-transition strength with predictions of the interacting boson model were found. Using a Monte Carlo code the γ-decay of the continuum of highly excited nuclei is described. Entry states, mean γ-energies, γ-spectra, mean multiplicities, multipolarities, and mean feeding times as well as e.g. their second moments were calculated for the reactions 58 Ni( 16 O,2p) 72 Se and 68 Zn( 12 C,2n) 78 Kr. The results are discussed and compared with experimental data. (HSI) [de

  12. Comparison and fit of the two and six band k.p models for the band edge structure of Pbsub(1-x)Snsub(x)Te

    International Nuclear Information System (INIS)

    Weissman, Y.

    1975-10-01

    The band edge structure of Pbsub(1-x)Snsub(x)Te is derived in detail using a two band ellipsoidal model and compared with a more rigorous calculation based on six bands. A quantitative comparison is made for two values of the energy gap, corresponding to the cases where x=0 and x=0.17. It was found that, for the occupied states in nondegenerate materials, both models are practically equivalent. Discrepancies may occur only in high degeneracies or deep inversion layers. The agreement between both models was significantly improved by introducing an effective energy gap in the two band model. It is suggested that the use of the effective energy gap may improve the agreement between the two band model and experiment whenever the details of the band edge structure enter the interpretation of the experimental results. (author)

  13. Effect of correlation on the band structure of α-cerium

    International Nuclear Information System (INIS)

    Rao, R.S.; Singh, R.P.

    1975-01-01

    The electronic band structure of f.c.c. phase of the rare earth metal cerium (α-cerium) has been calculated using a formulation of the crystal potential where correlation also has been included in addition to exchange. The Green's function method of Korringa-Kohn and Rostoker has been used due to obvious advantages in calculation. The calculations indicate that the s-d bands are hybridized with the f-levels but the f-bands are fairly narrow and lie slightly above the Fermi level. The structure of the bands is qualitatively similar to those of calculations by others except for a general shift of the entire set of bands by about 0.1 Ryd. Thd density of states has also been calculated from the bands obtained. The spin susceptibility of α-cerium has also been calculated using the Kohn-Sham method. However, the calculated additional contributions to the band structure values cannot still explain the large experimental values reported in the literature. (author)

  14. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    Science.gov (United States)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

    2015-01-01

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO2), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

  15. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    Energy Technology Data Exchange (ETDEWEB)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan, E-mail: alan.doolittle@ece.gatech.edu [Department of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

    2015-01-21

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO{sub 2}), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO{sub 2} has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

  16. Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

    International Nuclear Information System (INIS)

    Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

    2015-01-01

    The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO 2 ), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO 2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance

  17. Theoretical studies on band structure and optical properties of 3C-SiC by FPLAPW

    International Nuclear Information System (INIS)

    Xu, P.; Xie, C.; Xu, F.; Pan, H.

    2004-01-01

    Full text: SiC has attracted more interests because of its great technological importance in microelectronic and photoelectronic devices. We have studied the band structure and optical properties of 3C-SiC by using a Full Potential Linearized Augmented Plane Waves (FPLAPW) method. The partial density of states (DOS) of Si and C atoms as well as the band structure of 3C-SiC are presented. The calculated band gap is 1.30eV, which is much less than the experimental value. It is attributed to a deficiency of the local density theory. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With the band gap correction, the real part of the dielectric function has been derived from the imaginary part by Kramers Kronig (K-K) dispersion relationship. The calculated results are in good agreement with the results measured by Petalas et al. by using ultraviolet spectroscopic ellipsometry in the photon energy range of 5eV-10eV. The band-to-band transition can be identified from the critical points exhibited in the calculated dielectric function, which is consistent with the experimental results of Petalas et al. The refractive index, extinction coefficient and reflectivity have also been calculated from obtained dielectric function, which are in agreement with the experimental results of Logothetidis and Lambrecht

  18. Influence of strain on band structure of semiconductor nanostructures

    Directory of Open Access Journals (Sweden)

    Raičević Nevena

    2009-01-01

    Full Text Available The influence of the mechanical strain on the electronic structure of the asymmetric (In,GaAs/GaAs quantum well is considered. Both the direct influence of strain on the orbital part of the electronic structure and an indirect influence through the strain dependent Rashba and Dresselhaus Hamiltonians are taken into account. The analyzed quantum well is taken to have a triangular shape, and is oriented along the direction. For this direction, there exists both the intrinsic and strain-induced spin-orbit interaction. For all analyzed types of spin-orbit interaction, subband splittings depend linearly on the in-plane wave vector. On the other hand, the electronic structure for the Rashba type of the strain-induced spin-orbit interaction shows isotropic dependence in the k-space, while the electronic structure due to the Dresselhaus type shows anisotropy. Furthermore, the Rashba strain-induced spin-orbit interaction increases subband splitting, while the effect of the Dresselhaus Hamiltonian on the electronic structure is opposite to the intrinsic spin-orbit interaction for certain polar angles.

  19. Polar semiconductor heterojunction structure energy band diagram considerations

    International Nuclear Information System (INIS)

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

    2016-01-01

    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. Polar semiconductor heterojunction structure energy band diagram considerations

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Shuxun; Wen, Cheng P., E-mail: cpwen@ieee.org; Wang, Maojun; Hao, Yilong [Institute of Microelectronics, Peking University, Beijing (China)

    2016-03-28

    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.

  1. An open-structure sound insulator against low-frequency and wide-band acoustic waves

    Science.gov (United States)

    Chen, Zhe; Fan, Li; Zhang, Shu-yi; Zhang, Hui; Li, Xiao-juan; Ding, Jin

    2015-10-01

    To block sound, i.e., the vibration of air, most insulators are based on sealed structures and prevent the flow of the air. In this research, an acoustic metamaterial adopting side structures, loops, and labyrinths, arranged along a main tube, is presented. By combining the accurately designed side structures, an extremely wide forbidden band with a low cut-off frequency of 80 Hz is produced, which demonstrates a powerful low-frequency and wide-band sound insulation ability. Moreover, by virtue of the bypass arrangement, the metamaterial is based on an open structure, and thus air flow is allowed while acoustic waves can be insulated.

  2. Precise fabrication of X-band accelerating structure

    International Nuclear Information System (INIS)

    Higo, T.; Sakai, H.; Higashi, Y.; Koike, S.; Takatomi, T.

    1994-01-01

    An accelerating structure with a/λ=0.16 is being fabricated to study a precise fabrication method. A frequency control of each cell better than 10 -4 level is required to realize a detuned structure. The present machining level is nearly 1 MHz/11.4 GHz in relative frequency error, which just satisfies the above requirement. To keep this machining precision, the diffusion bonding technique is found preferable to join the cells. Various diffusion conditions were tried. The frequency change can be less than 1 MHz/11.4 GHz and it can be controlled well better than that. (author)

  3. Electrical properties and band structures of Pb1-x Snx Te alloys

    International Nuclear Information System (INIS)

    Ocio, Miguel

    1972-01-01

    Both p type alloys Pb 0.72 Sn 0.28 Te and Pb 0.53 Sn 0.47 Te have been studied in the present work. The main obtained results are the following: the materials have a two-valence band structure, the first band following non-parabolic Cohen's dispersion law; at low temperatures, carriers are scattered by ionized impurities; the Coulomb potentials being screened almost completely, impurities act like neutral centers. At room temperature, scattering by acoustic modes can explain lattice mobility behavior; reversing of the thermo-power, for samples with carrier densities of about 10 20 cm -3 , is possibly due to inter-band scattering between both valence bands; a very simple picture of the band parameters variations as a function of alloy fraction is suggested. (author) [fr

  4. 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.

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

    International Nuclear Information System (INIS)

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

    2011-01-01

    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.

  6. Band structure features of nonlinear optical yttrium aluminium borate crystal

    Czech Academy of Sciences Publication Activity Database

    Reshak, Ali H; Auluck, S.; Majchrowski, A.; Kityk, I. V.

    2008-01-01

    Roč. 10, č. 10 (2008), s. 1445-1448 ISSN 1293-2558 Institutional research plan: CEZ:AV0Z60870520 Keywords : Electronic structure * DFF * FPLAPW * LDA Subject RIV: BO - Biophysics Impact factor: 1.742, year: 2008

  7. Effect of eddy current damping on phononic band gaps generated by locally resonant periodic structures

    Science.gov (United States)

    Ozkaya, Efe; Yilmaz, Cetin

    2017-02-01

    The effect of eddy current damping on a novel locally resonant periodic structure is investigated. The frequency response characteristics are obtained by using a lumped parameter and a finite element model. In order to obtain wide band gaps at low frequencies, the periodic structure is optimized according to certain constraints, such as mass distribution in the unit cell, lower limit of the band gap, stiffness between the components in the unit cell, the size of magnets used for eddy current damping, and the number of unit cells in the periodic structure. Then, the locally resonant periodic structure with eddy current damping is manufactured and its experimental frequency response is obtained. The frequency response results obtained analytically, numerically and experimentally match quite well. The inclusion of eddy current damping to the periodic structure decreases amplitudes of resonance peaks without disturbing stop band width.

  8. 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.

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

    Science.gov (United States)

    Fujimori, Shin-ichi

    2016-04-20

    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 eV) or high-energy synchrotron radiations (hν >/~ 400 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 CeMIn5(M = Rh, Ir, and Co) and YbRh2Si2 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 U5f compounds such as UFeGa5, their electronic structures can be well-described by the band-structure calculation assuming that all U5f electrons are itinerant. In contrast, the band structures of localized U5f compounds such as UPd3 and UO2 are essentially explained by the localized model that treats U5f electrons as localized core states. In regards to heavy fermion U-based compounds such as the hidden-order compound URu2Si2, their electronic structures exhibit complex behaviors. Their overall band structures are generally well-explained by the band-structure calculation, whereas the states in the vicinity of EF show some deviations due to electron correlation effects. Furthermore, the electronic structures of URu2Si2 in the paramagnetic and hidden-order phases are

  10. 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.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

    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 K 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

  12. 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.

  13. Quasiparticle Level Alignment for Photocatalytic Interfaces.

    Science.gov (United States)

    Migani, Annapaoala; Mowbray, Duncan J; Zhao, Jin; Petek, Hrvoje; Rubio, Angel

    2014-05-13

    Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. Standard density functional theory (DFT)-based methods have proven unable to provide a quantitative description of this level alignment. This requires a proper treatment of the anisotropic screening, necessitating the use of quasiparticle (QP) techniques. However, the computational complexity of QP algorithms has meant a quantitative description of interfacial levels has remained elusive. We provide a systematic study of a prototypical interface, bare and methanol-covered rutile TiO2(110) surfaces, to determine the type of many-body theory required to obtain an accurate description of the level alignment. This is accomplished via a direct comparison with metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), and two-photon photoemission (2PP) spectroscopy. We consider GGA DFT, hybrid DFT, and G0W0, scQPGW1, scQPGW0, and scQPGW QP calculations. Our results demonstrate that G0W0, or our recently introduced scQPGW1 approach, are required to obtain the correct alignment of both the highest occupied and lowest unoccupied interfacial molecular levels (HOMO/LUMO). These calculations set a new standard in the interpretation of electronic structure probe experiments of complex organic molecule/semiconductor interfaces.

  14. Triple photonic band-gap structure dynamically induced in the presence of spontaneously generated coherence

    International Nuclear Information System (INIS)

    Gao Jinwei; Bao Qianqian; Wan Rengang; Cui Cuili; Wu Jinhui

    2011-01-01

    We study a cold atomic sample coherently driven into the five-level triple-Λ configuration for attaining a dynamically controlled triple photonic band-gap structure. Our numerical calculations show that three photonic band gaps with homogeneous reflectivities up to 92% can be induced on demand around the probe resonance by a standing-wave driving field in the presence of spontaneously generated coherence. All these photonic band gaps are severely malformed with probe reflectivities declining rapidly to very low values when spontaneously generated coherence is gradually weakened. The triple photonic band-gap structure can also be attained in a five-level chain-Λ system of cold atoms in the absence of spontaneously generated coherence, which however requires two additional traveling-wave fields to couple relevant levels.

  15. Strain effect on graphene nanoribbon carrier statistic in the presence of non-parabolic band structure

    International Nuclear Information System (INIS)

    Izuani Che Rosid, N A; Ahmadi, M T; Ismail, Razali

    2016-01-01

    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. (paper)

  16. Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure

    Science.gov (United States)

    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 WLAN) at 3.5 GHz and 5.5 GHz, respectively. PMID:24170984

  17. 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.

  18. Electronic structure of the copper oxides: Band picture versus correlated behavior

    Energy Technology Data Exchange (ETDEWEB)

    Pickett, W E; Cohen, R E; Singh, D [Naval Research Lab., Washington, DC (USA); Krakauer, H [Coll. of William and Mary, Williamsburg, VA (USA)

    1989-12-01

    In the 2 1/2 years since the discovery of the high temperature superconducting copper oxides, a great deal has been learned from experiment about their behavior. From the theoretical side, there continues to be developments both within the band picture and from the model Hamiltonian viewpoint emphasizing correlations. In this paper we discuss briefly these complementary viewpoints in relation to certain of the experimental data. Due to our background in the band structure area, we approach the discussion by evaluating which phenomena can be (or has been) accounted for by the standard band approach, and point out which properties appear to require more intricate treatments of correlation. (orig.).

  19. Terahertz emission from CdHgTe/HgTe quantum wells with an inverted band structure

    Energy Technology Data Exchange (ETDEWEB)

    Vasilyev, Yu. B., E-mail: Yu.Vasilyev@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Mikhailov, N. N. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Vasilyeva, G. Yu.; Ivánov, Yu. L.; Zakhar’in, A. O.; Andrianov, A. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Vorobiev, L. E.; Firsov, D. A. [Peter the Great Saint-Petersburg Polytechnic University (Russian Federation); Grigoriev, M. N. [Ustinov Baltic State Technical University “VOENMEKh” (Russian Federation); Antonov, A. V.; Ikonnikov, A. V.; Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-07-15

    The terahertz electroluminescence from Cd{sub 0.7}Hg{sub 0.3}Te/HgTe quantum wells with an inverted band structure in lateral electric fields is experimentally detected and studied. The emission-spectrum maximum for wells 6.5 and 7 nm wide is near 6 meV which corresponds to interband optical transitions. The emission is explained by state depletion in the valence band and conduction band filling due to Zener tunneling, which is confirmed by power-law current–voltage characteristics.

  20. Crystal structure, electrical properties and electronic band structure of tantalum ditelluride

    CERN Document Server

    Vernes, A; Bensch, W; Heid, W; Naether, C

    1998-01-01

    Motivated by the unexpectedly strong influence of the Te atoms on the structural and bonding properties of the transition metal tellurides, we have performed a detailed study of TaTe sub 2. Experimentally, this comprises a crystal structure determination as well as electrical resistivity measurements. The former analysis leads to an accurate update of the structural data reported in the 1960s, while the latter provides evidence for the mainly electronic character of scattering processes leading to the electrical conductivity. In addition, the electronic properties of TaTe sub 2 have been calculated using the TB-LMTO method. The partial density of states reflects the close connection of the Ta zigzag chains and the Te-Te network. This finding explains the charge transfer in the system in a rather simple way. The orthogonal-orbital character of the bands proved the existence of pi-bonds. The Fermi-surface study supports the interpretation of the experimental resistivity measurements. (author)

  1. Justifying quasiparticle self-consistent schemes via gradient optimization in Baym-Kadanoff theory.

    Science.gov (United States)

    Ismail-Beigi, Sohrab

    2017-09-27

    The question of which non-interacting Green's function 'best' describes an interacting many-body electronic system is both of fundamental interest as well as of practical importance in describing electronic properties of materials in a realistic manner. Here, we study this question within the framework of Baym-Kadanoff theory, an approach where one locates the stationary point of a total energy functional of the one-particle Green's function in order to find the total ground-state energy as well as all one-particle properties such as the density matrix, chemical potential, or the quasiparticle energy spectrum and quasiparticle wave functions. For the case of the Klein functional, our basic finding is that minimizing the length of the gradient of the total energy functional over non-interacting Green's functions yields a set of self-consistent equations for quasiparticles that is identical to those of the quasiparticle self-consistent GW (QSGW) (van Schilfgaarde et al 2006 Phys. Rev. Lett. 96 226402-4) approach, thereby providing an a priori justification for such an approach to electronic structure calculations. In fact, this result is general, applies to any self-energy operator, and is not restricted to any particular approximation, e.g., the GW approximation for the self-energy. The approach also shows that, when working in the basis of quasiparticle states, solving the diagonal part of the self-consistent Dyson equation is of primary importance while the off-diagonals are of secondary importance, a common observation in the electronic structure literature of self-energy calculations. Finally, numerical tests and analytical arguments show that when the Dyson equation produces multiple quasiparticle solutions corresponding to a single non-interacting state, minimizing the length of the gradient translates into choosing the solution with largest quasiparticle weight.

  2. Band structure and phonon properties of lithium fluoride at high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Panchal, J. M., E-mail: amitjignesh@yahoo.co.in [Government Engineering College, Gandhinagar 382028, Gujarat (India); Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India); Joshi, Mitesh [Government Polytechnic for Girls, Athwagate, Surat395001, Gujarat (India); Gajjar, P. N., E-mail: pngajjar@rediffmail.com [Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India)

    2016-05-23

    High pressure structural and electronic properties of Lithium Fluoride (LiF) have been studied by employing an ab-initio pseudopotential method and a linear response scheme within the density functional theory (DFT) in conjunction with quasi harmonic Debye model. The band structure and electronic density of states conforms that the LiF is stable and is having insulator behavior at ambient as well as at high pressure up to 1 Mbar. Conclusions based on Band structure, phonon dispersion and phonon density of states are outlined.

  3. 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...... behavior of these structures, and the computed results generally match well with ones published in the literature. It is also found that the FDTD method is a robust, versatile, and powerful numerical technique to perform such numerical studies. The proposed PBG filter structures may be applied in microwave...

  4. Band structure and phonon properties of lithium fluoride at high pressure

    International Nuclear Information System (INIS)

    Panchal, J. M.; Joshi, Mitesh; Gajjar, P. N.

    2016-01-01

    High pressure structural and electronic properties of Lithium Fluoride (LiF) have been studied by employing an ab-initio pseudopotential method and a linear response scheme within the density functional theory (DFT) in conjunction with quasi harmonic Debye model. The band structure and electronic density of states conforms that the LiF is stable and is having insulator behavior at ambient as well as at high pressure up to 1 Mbar. Conclusions based on Band structure, phonon dispersion and phonon density of states are outlined.

  5. X-BAND LINEAR COLLIDER R and D IN ACCELERATING STRUCTURES THROUGH ADVANCED COMPUTING

    International Nuclear Information System (INIS)

    Li, Z

    2004-01-01

    This paper describes a major computational effort that addresses key design issues in the high gradient accelerating structures for the proposed X-band linear collider, GLC/NLC. Supported by the US DOE's Accelerator Simulation Project, SLAC is developing a suite of parallel electromagnetic codes based on unstructured grids for modeling RF structures with higher accuracy and on a scale previously not possible. The new simulation tools have played an important role in the R and D of X-Band accelerating structures, in cell design, wakefield analysis and dark current studies

  6. Polarization-dependent diffraction in all-dielectric, twisted-band structures

    Energy Technology Data Exchange (ETDEWEB)

    Kardaś, Tomasz M.; Jagodnicka, Anna; Wasylczyk, Piotr, E-mail: pwasylcz@fuw.edu.pl [Photonic Nanostructure Facility, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warszawa (Poland)

    2015-11-23

    We propose a concept for light polarization management: polarization-dependent diffraction in all-dielectric microstructures. Numerical simulations of light propagation show that with an appropriately configured array of twisted bands, such structures may exhibit zero birefringence and at the same time diffract two circular polarizations with different efficiencies. Non-birefringent structures as thin as 3 μm have a significant difference in diffraction efficiency for left- and right-hand circular polarizations. We identify the structural parameters of such twisted-band matrices for optimum performance as circular polarizers.

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

    International Nuclear Information System (INIS)

    Aly, Arafa H; Mehaney, Ahmed

    2016-01-01

    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. (paper)

  8. Calculation of band alignments and quantum confinement effects in zero- and one-dimensional pseudomorphic structures

    International Nuclear Information System (INIS)

    Yang, M.; Sturm, J.C.; Prevost, J.

    1997-01-01

    The strain field distributions and band lineups of zero-dimensional and one-dimensional strained pseudomorphic semiconductor particles inside a three-dimensional matrix of another semiconductor have been studied. The resulting strain in the particle and the matrix leads to band alignments considerably different from that in the conventional two-dimensional (2D) pseudomorphic growth case. The models are first applied to an ideal spherical and cylindrical Si 1-x Ge x particle in a large Si matrix. In contrast to the 2D case, the band alignments for both structures are predicted to be strongly type II, where the conduction-band edge and the valence-band edge of the Si matrix are both significantly lower than those in the Si 1-x Ge x inclusion, respectively. Band lineups and the lowest electron endash heavy-hole transition energies of a pseudomorphic V-groove Si 1-x Ge x quantum wire inside a large Si matrix have been calculated numerically for different size structures. The photoluminescence energies of a large Si 1-x Ge x V-groove structure on Si will be lower than those of conventional 2D strained Si 1-x Ge x for similar Ge contents. copyright 1997 The American Physical Society

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

    Czech Academy of Sciences Publication Activity Database

    Markoš, P.; Kuzmiak, Vladimír

    2016-01-01

    Roč. 94, č. 3 (2016), č. článku 033845. ISSN 2469-9926 R&D Projects: GA MŠk(CZ) LD14028 Institutional support: RVO:67985882 Keywords : Crystal structure * Photonic crystals * Two-dimensional arrays Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.925, year: 2016

  10. Structural analysis, electronic properties, and band gaps of a graphene nanoribbon: A new 2D materials

    Science.gov (United States)

    Dass, Devi

    2018-03-01

    Graphene nanoribbon (GNR), a new 2D carbon nanomaterial, has some unique features and special properties that offer a great potential for interconnect, nanoelectronic devices, optoelectronics, and nanophotonics. This paper reports the structural analysis, electronic properties, and band gaps of a GNR considering different chirality combinations obtained using the pz orbital tight binding model. In structural analysis, the analytical expressions for GNRs have been developed and verified using the simulation for the first time. It has been found that the total number of unit cells and carbon atoms within an overall unit cell and molecular structure of a GNR have been changed with the change in their chirality values which are similar to the values calculated using the developed analytical expressions thus validating both the simulation as well as analytical results. Further, the electronic band structures at different chirality values have been shown for the identification of metallic and semiconductor properties of a GNR. It has been concluded that all zigzag edge GNRs are metallic with very small band gaps range whereas all armchair GNRs show both the metallic and semiconductor nature with very small and high band gaps range. Again, the total number of subbands in each electronic band structure is equal to the total number of carbon atoms present in overall unit cell of the corresponding GNR. The semiconductors GNRs can be used as a channel material in field effect transistor suitable for advanced CMOS technology whereas the metallic GNRs could be used for interconnect.

  11. 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...

  12. An Optimized, Grid Independent, Narrow Band Data Structure for High Resolution Level Sets

    DEFF Research Database (Denmark)

    Nielsen, Michael Bang; Museth, Ken

    2004-01-01

    enforced by the convex boundaries of an underlying cartesian computational grid. Here we present a novel very memory efficient narrow band data structure, dubbed the Sparse Grid, that enables the representation of grid independent high resolution level sets. The key features our new data structure are...

  13. Formation of heavy d-electron quasiparticles in Sr3Ru2O7

    International Nuclear Information System (INIS)

    Allan, M P; Tamai, A; Rozbicki, E; King, P D C; Meevasana, W; Perry, R S; Mercure, J F; Mackenzie, A P; Fischer, M H; Wang, M A; Lee, Jinho; Kim, E-A; Lawler, M J; Shen, K M; Voss, J; Fennie, C J; Thirupathaiah, S; Rienks, E; Fink, J; Tennant, D A

    2013-01-01

    The phase diagram of Sr 3 Ru 2 O 7 shows hallmarks of strong electron correlations despite the modest Coulomb interaction in the Ru 4d shell. We use angle-resolved photoelectron spectroscopy measurements to provide microscopic insight into the formation of the strongly renormalized heavy d-electron liquid that controls the physics of Sr 3 Ru 2 O 7 . Our data reveal itinerant Ru 4d-states confined over large parts of the Brillouin zone to an energy range of <6 meV, nearly three orders of magnitude lower than the bare band width. We show that this energy scale agrees quantitatively with a characteristic thermodynamic energy scale associated with quantum criticality and illustrate how it arises from a combination of back-folding due to a structural distortion and the hybridization of light and strongly renormalized, heavy quasiparticle bands. The resulting heavy Fermi liquid has a marked k-dependence of the renormalization which we relate to orbital mixing along individual Fermi surface sheets. (paper)

  14. Research on the Band Gap Characteristics of Two-Dimensional Phononic Crystals Microcavity with Local Resonant Structure

    Directory of Open Access Journals (Sweden)

    Mao Liu

    2015-01-01

    Full Text Available A new two-dimensional locally resonant phononic crystal with microcavity structure is proposed. The acoustic wave band gap characteristics of this new structure are studied using finite element method. At the same time, the corresponding displacement eigenmodes of the band edges of the lowest band gap and the transmission spectrum are calculated. The results proved that phononic crystals with microcavity structure exhibited complete band gaps in low-frequency range. The eigenfrequency of the lower edge of the first gap is lower than no microcavity structure. However, for no microcavity structure type of quadrilateral phononic crystal plate, the second band gap disappeared and the frequency range of the first band gap is relatively narrow. The main reason for appearing low-frequency band gaps is that the proposed phononic crystal introduced the local resonant microcavity structure. This study provides a good support for engineering application such as low-frequency vibration attenuation and noise control.

  15. Isotropic Kink and Quasiparticle Excitations in the Three-Dimensional Perovskite Manganite La_{0.6}Sr_{0.4}MnO_{3}.

    Science.gov (United States)

    Horiba, Koji; Kitamura, Miho; Yoshimatsu, Kohei; Minohara, Makoto; Sakai, Enju; Kobayashi, Masaki; Fujimori, Atsushi; Kumigashira, Hiroshi

    2016-02-19

    In order to reveal the many-body interactions in three-dimensional perovskite manganites that show colossal magnetoresistance, we performed an in situ angle-resolved photoemission spectroscopy on La_{0.6}Sr_{0.4}MnO_{3} and investigated the behavior of quasiparticles. We observed quasiparticle peaks near the Fermi momentum in both the electron and the hole bands, and clear kinks throughout the entire hole Fermi surface in the band dispersion. This isotropic behavior of quasiparticles and kinks suggests that polaronic quasiparticles produced by the coupling of electrons with Jahn-Teller phonons play an important role in the colossal magnetoresistance properties of the ferromagnetic metallic phase of three-dimensional manganites.

  16. Infrared absorption, multiphonon processes and time reversal effect on Si and Ge band structure

    International Nuclear Information System (INIS)

    Kunert, H.W.; Machatine, A.G.J.; Malherbe, J.B.; Barnas, J.; Hoffmann, A.; Wagner, M.R.

    2008-01-01

    We have examined the effect of Time Reversal Symmetry (TRS) on vibrational modes and on the electronic band structure of Si and Ge. Most of the primary non-interacting modes are not affected by TRS. Only phonons originating from high symmetry lines S and A of the Brillouin Zone (BZ) indicate extra degeneracy. Selection rules for some two and three phonons originating from high symmetry lines are determined. The states of electrons and holes described by electronic band structure due to spin-inclusion are assigned by spinor representations of the double space group. Inclusion of the TRS into the band structure results in extra degeneracy of electrons and holes, and therefore optical selection rules suppose to be modified

  17. Quasiparticle branch mixing rates in superconducting aluminum

    International Nuclear Information System (INIS)

    Chi, C.C.; Clarke, J.

    1979-01-01

    The kinetic equation is used to compute the elastic and inelastic quasiparticle branch mixing rates for a superconducting film into which quasiparticles are injected via a tunnel barrier from a second superconducting film. Representative graphs are presented of the steady-state quasiparticle distribution, the quasiparticle charge imbalance Q* versus injection current, the charge relaxation rate tau -1 /sub Q/* vs Δ/k/sub B/T/sub c/ for several values of elastic scattering rate, and the quasiparticle branch relaxation rate tau -1 /sub Q/ as a function of energy. The quasiparticle potential developed in the injection film is related to tau -1 /sub Q/, and thence to tau -1 0 , a characteristic electron-phonon scattering time. Detailed measurements of tau/sub Q/ are reported for films of superconducting Al, some of which were doped with oxygen to give a range of transition temperatures from 1.2 to 2.1 K. From the dependence of tau -1 /sub Q/* on Δ/k/sub B/T/sub c/, values are deduced for the gap anisotropy of the films. In the cleanest samples, tau 0 or approx. = 2Δ) mean-free-path measurements, but a factor of about 4 smaller than that obtained from recombination time measurements and theoretical calculations. The value of tau -1 /sub o/ in the Al films increases with the transition temperature T/sub c/ as T 5 /sub c/ or T 6 /sub c/, instead of T 3 /sub c/ as predicted by simple theory. It is suggested that the rapid increase of tau -1 0 with T/sub c/ may arise from either a strong dependence of α 2 F (ω) on T/sub c/ or from a small concentration of magnetic impurities

  18. Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot

    Science.gov (United States)

    Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Song, Ruifang

    2015-01-01

    In this paper, a novel two-dimensional phononic crystal composed of periodic Jerusalem cross slot in air matrix with a square lattice is presented. The dispersion relations and the transmission coefficient spectra are calculated by using the finite element method based on the Bloch theorem. The formation mechanisms of the band gaps are analyzed based on the acoustic mode analysis. Numerical results show that the proposed phononic crystal structure can yield large band gaps in the low-frequency range. The formation mechanism of opening the acoustic band gaps is mainly attributed to the resonance modes of the cavities inside the Jerusalem cross slot structure. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the band gaps can be modulated in an extremely large frequency range by the geometry parameters such as the slot length and width. These properties of acoustic waves in the proposed phononic crystals can potentially be applied to optimize band gaps and generate low-frequency filters and waveguides.

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

    International Nuclear Information System (INIS)

    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 2 and YH 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 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 2 lattice. These experimental results also suggest that, in contrast to recent calculations, LaH 3 is a small-band-gap semiconductor

  20. Topological Magnon Bands in a Kagome Lattice Ferromagnet.

    Science.gov (United States)

    Chisnell, R; Helton, J S; Freedman, D E; Singh, D K; Bewley, R I; Nocera, D G; Lee, Y S

    2015-10-02

    There is great interest in finding materials possessing quasiparticles with topological properties. Such materials may have novel excitations that exist on their boundaries which are protected against disorder. We report experimental evidence that magnons in an insulating kagome ferromagnet can have a topological band structure. Our neutron scattering measurements further reveal that one of the bands is flat due to the unique geometry of the kagome lattice. Spin wave calculations show that the measured band structure follows from a simple Heisenberg Hamiltonian with a Dzyaloshinkii-Moriya interaction. This serves as the first realization of an effectively two-dimensional topological magnon insulator--a new class of magnetic material that should display both a magnon Hall effect and protected chiral edge modes.

  1. 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.

  2. Energy band structure of Cr by the Slater-Koster interpolation scheme

    International Nuclear Information System (INIS)

    Seifu, D.; Mikusik, P.

    1986-04-01

    The matrix elements of the Hamiltonian between nine localized wave-functions in tight-binding formalism are derived. The symmetry adapted wave-functions and the secular equations are formed by the group theory method for high symmetry points in the Brillouin zone. A set of interaction integrals is chosen on physical ground and fitted via the Slater-Koster interpolation scheme to the abinito band structure of chromium calculated by the Green function method. Then the energy band structure of chromium is interpolated and extrapolated in the Brillouin zone. (author)

  3. Convergence of quasiparticle self-consistent GW calculations of transition metal monoxides

    OpenAIRE

    Das, Suvadip; Coulter, John E.; Manousakis, Efstratios

    2014-01-01

    Finding an accurate ab initio approach for calculating the electronic properties of transition metal oxides has been a problem for several decades. In this paper, we investigate the electronic structure of the transition metal monoxides MnO, CoO, and NiO in their undistorted rock-salt structure within a fully iterated quasiparticle self-consistent GW (QPscGW) scheme. We study the convergence of the QPscGW method, i.e., how the quasiparticle energy eigenvalues and wavefunctions converge as a f...

  4. Superconducting quasiparticle lifetimes due to spin-fluctuation scattering

    International Nuclear Information System (INIS)

    Quinlan, S.M.; Scalapino, D.J.; Bulut, N.

    1994-01-01

    Superconducting quasiparticle lifetimes associated with spin-fluctuation scattering are calculated. A Berk-Schrieffer interaction with an irreducible susceptibility given by a BCS form is used to model the quasiparticle damping due to spin fluctuations. Results are presented for both s-wave and d-wave gaps. Also, quasiparticle lifetimes due to impurity scattering are calculated for a d-wave superconductor

  5. Band structure and optical properties of sinusoidal superlattices: ZnSe1-xTex

    International Nuclear Information System (INIS)

    Yang, G.; Lee, S.; Furdyna, J. K.

    2000-01-01

    This paper examines the band structure and optical selection rules in superlattices with a sinusoidal potential profile. The analysis is motivated by the recent successful fabrication of high quality ZnSe 1-x Te x superlattices in which the composition x varies sinusoidally along the growth direction. Although the band alignment in the ZnSe 1-x Te x sinusoidal superlattices is staggered (type II), they exhibit unexpectedly strong photoluminescence, thus suggesting interesting optical behavior. The band structure of such sinusoidal superlattices is formulated in terms of the nearly-free-electron (NFE) approximation, in which the superlattice potential is treated as a perturbation. The resulting band structure is unique, characterized by a single minigap separating two wide, free-electron-like subbands for both electrons and holes. Interband selection rules are derived for optical transitions involving conduction and valence-band states at the superlattice Brillouin-zone center, and at the zone edge. A number of transitions are predicted due to wave-function mixing of different subband states. It should be noted that the zone-center and zone-edge transitions are especially easy to distinguish in these superlattices because of the large width of the respective subbands. The results of the NFE approximation are shown to hold surprisingly well over a wide range of parameters, particularly when the period of the superlattice is short. (c) 2000 The American Physical Society

  6. Effect of ladder diagrams on optical absorption spectra in a quasiparticle self-consistent GW framework

    Science.gov (United States)

    Cunningham, Brian; Grüning, Myrta; Azarhoosh, Pooya; Pashov, Dimitar; van Schilfgaarde, Mark

    2018-03-01

    We present an approach to calculate the optical absorption spectra that combines the quasiparticle self-consistent GW method [Phys. Rev. B 76, 165106 (2007), 10.1103/PhysRevB.76.165106] for the electronic structure with the solution of the ladder approximation to the Bethe-Salpeter equation for the macroscopic dielectric function. The solution of the Bethe-Salpeter equation has been implemented within an all-electron framework, using a linear muffin-tin orbital basis set, with the contribution from the nonlocal self-energy to the transition dipole moments (in the optical limit) evaluated explicitly. This approach addresses those systems whose electronic structure is poorly described within the standard perturbative GW approaches with density-functional theory calculations as a starting point. The merits of this approach have been exemplified by calculating optical absorption spectra of a strongly correlated transition metal oxide, NiO, and a narrow gap semiconductor, Ge. In both cases, the calculated spectrum is in good agreement with the experiment. It is also shown that for systems whose electronic structure is well-described within the standard perturbative GW , such as Si, LiF, and h -BN , the performance of the present approach is in general comparable to the standard GW plus Bethe-Salpeter equation. It is argued that both vertex corrections to the electronic screening and the electron-phonon interaction are responsible for the observed systematic overestimation of the fundamental band gap and spectrum onset.

  7. Quasi-particles and quantum condensate in the Quantum Chromodynamics

    International Nuclear Information System (INIS)

    Herrmann, J.

    1987-01-01

    The non-perturbative structure of Quantum Chromodynamics is investigated with the help of a generalisation of the formalism of Green's functions according to Gorkow and Nambu's studies in the theory of superconductivity methods. Taking into account the existence of the gluon condensation, the self-energy of the gluon-quasi-particles in the form of integral-equations is calculated with the help of modified rules for Feynman diagrams. The form of these equations implies the existence of particular solutions with an energy gap in the spectrum of the quasi-particles and a phase transition at a critical momentum. (author)

  8. The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

    International Nuclear Information System (INIS)

    Kevin Jerome Sutherland

    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. 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.

  10. 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

    of these for nonlinear problems is impossible or cumbersome, since Floquet theory is applicable for linear systems only. Thus the nonlinear effects for periodic structures are not yet fully uncovered, while at the same time applica-tions may demand effects of nonlinearity on structural response to be accounted for....... The present work deals with analytically predicting dynamic responses for nonlinear continuous elastic periodic structures. Specifically, the effects of weak nonlinearity on the dispersion re-lation and frequency band-gaps of a periodic Bernoulli-Euler beam performing bending os-cillations are analyzed......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...

  11. Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor

    Science.gov (United States)

    Nakayama, K.; Miyata, Y.; Phan, G. N.; Sato, T.; Tanabe, Y.; Urata, T.; Tanigaki, K.; Takahashi, T.

    2014-12-01

    We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (Tc˜8 K ), which exhibits a tetragonal-to-orthorhombic structural transition at Ts˜90 K . At low temperature, we found splitting of the energy bands as large as 50 meV at the M point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to T ˜110 K , slightly above Ts, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe.

  12. High-spin structure of 121Xe: triaxiality, band termination and signature inversion

    International Nuclear Information System (INIS)

    Timar, J.; Paul, E.S.; Beausang, C.W.; Joyce, M.J.; Sharpey-Schafer, J.F.

    1995-01-01

    High-spin states of the odd-neutron 121 Xe nucleus have been studied with Eurogam using the 96 Zr( 30 Si, 5n) 121 Xe fusion-evaporation reaction. The level scheme has been extended up to a tentative spin of 67/2h at an excitation energy of ∼ 14 MeV. Several new rotational bands have been observed and the previously known bands extended. Two of them lose their regular character at high spins, which may be interpreted as transition from collective behaviour to a regime of noncollective oblate states. The deduced high-spin structure is compared to Woods-Saxon TRS cranking and CSM calculations. Configurations of the bands have been suggested. The νh 1 1/2 band is interpreted as having a triaxial shape. Signature inversion and an unexpectedly large staggering of the B(M1)/B(E2) ratios has been found for one of the bands. Enhanced E1 transitions have been observed between the νd 5/2 and the νh 1 1/2 bands. (orig.)

  13. Estimation of photonic band gap in the hollow core cylindrical multilayer structure

    Science.gov (United States)

    Chourasia, Ritesh Kumar; Singh, Vivek

    2018-04-01

    The propagation characteristic of two hollow core cylindrical multilayer structures having high and low refractive index contrast of cladding regions have been studied and compared at two design wavelengths i.e. 1550 nm and 632.8 nm. With the help of transfer matrix method a relation between the incoming light wave and outgoing light wave has been developed using the boundary matching technique. In high refractive index contrast, small numbers of layers are sufficient to provide perfect band gap in both design wavelengths. The spectral position and width of band gap is highly depending on the optical path of incident light in all considered cases. For sensing application, the sensitivity of waveguide can be obtained either by monitoring the width of photonic band gap or by monitoring the spectral shift of photonic band gap. Change in the width of photonic band gap with the core refractive index is larger in high refractive index contrast of cladding materials. However, in the case of monitoring the spectral shift of band gap, the obtained sensitivity is large for low refractive index contrast of cladding materials and further it increases with increase of design wavelength.

  14. Metal-like Band Structures of Ultrathin Si {111} and {112} Surface Layers Revealed through Density Functional Theory Calculations.

    Science.gov (United States)

    Tan, Chih-Shan; Huang, Michael H

    2017-09-04

    Density functional theory calculations have been performed on Si (100), (110), (111), and (112) planes with tunable number of planes for evaluation of their band structures and density of states profiles. The purpose is to see whether silicon can exhibit facet-dependent properties derived from the presence of a thin surface layer having different band structures. No changes have been observed for single to multiple layers of Si (100) and (110) planes with a consistent band gap between the valence band and the conduction band. However, for 1, 2, 4, and 5 Si (111) and (112) planes, metal-like band structures were obtained with continuous density of states going from the valence band to the conduction band. For 3, 6, and more Si (111) planes, as well as 3 and 6 Si (112) planes, the same band structure as that seen for Si (100) and (110) planes has been obtained. Thus, beyond a layer thickness of five Si (111) planes at ≈1.6 nm, normal semiconductor behavior can be expected. The emergence of metal-like band structures for the Si (111) and (112) planes are related to variation in Si-Si bond length and bond distortion plus 3s and 3p orbital electron contributions in the band structure. This work predicts possession of facet-dependent electrical properties of silicon with consequences in FinFET transistor design. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Hybrid functional band gap calculation of SnO6 containing perovskites and their derived structures

    International Nuclear Information System (INIS)

    Lee, Hyewon; Cheong, S.W.; Kim, Bog G.

    2015-01-01

    We have studied the properties of SnO 6 octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO 6 containing perovskites. We also have expended the hybrid density functional calculation to the ASnO 3 /A'SnO 3 system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO 6 containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO 3 for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO 6 octahedrons are plotted as polyhedron. (b) Band gap of ASnO 3 as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO 3 /A'SnO 3 superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO 3 , [001] ordered superlattices, and [111] ordered superlattices of ASnO 3 /A'SnO 3 as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO 3 and ASnO 3 /A'SnO 3 . • The band gap of ASnO 3 using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap

  16. Lightwave-driven quasiparticle collisions on a sub-cycle timescale

    Science.gov (United States)

    Langer, F.; Hohenleutner, M.; Schmid, C.; Poellmann, C.; Nagler, P.; Korn, T.; Schüller, C.; Sherwin, M. S.; Huttner, U.; Steiner, J. T.; Koch, S. W.; Kira, M.; Huber, R.

    2016-01-01

    Ever since Ernest Rutherford first scattered α-particles from gold foils1, collision experiments have revealed unique insights into atoms, nuclei, and elementary particles2. In solids, many-body correlations also lead to characteristic resonances3, called quasiparticles, such as excitons, dropletons4, polarons, or Cooper pairs. Their structure and dynamics define spectacular macroscopic phenomena, ranging from Mott insulating states via spontaneous spin and charge order to high-temperature superconductivity5. Fundamental research would immensely benefit from quasiparticle colliders, but the notoriously short lifetimes of quasiparticles6 have challenged practical solutions. Here we exploit lightwave-driven charge transport7–24, the backbone of attosecond science9–13, to explore ultrafast quasiparticle collisions directly in the time domain: A femtosecond optical pulse creates excitonic electron–hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying wave packet dynamics, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands17–19 of the optical excitation. A full quantum theory explains our observations microscopically. This approach opens the door to collision experiments with a broad variety of complex quasiparticles and suggests a promising new way of sub-femtosecond pulse generation. PMID:27172045

  17. Renormalized plasma turbulence theory: A quasiparticle picture

    International Nuclear Information System (INIS)

    DuBois, D.F.

    1981-01-01

    A general renormalized statistical theory of Vlasov turbulence is given which proceeds directly from the Vlasov equation and does not assume prior knowledge of sophisticated field-theoretic techniques. Quasiparticles are the linear excitations of the turbulent system away from its instantaneous mean (ensemble-averaged) state or background; the properties of this background state ''dress'' or renormalize the quasiparticle responses. It is shown that all two-point responses (including the dielectric) and all two-point correlation functions can be completely described by the mean distribution function and three fundamental quantities. Two of these are the quasiparticle responses: the propagator and the potential source: which measure, respectively, the separate responses of the mean distribution function and the mean electrostatic potential to functional changes in an external phase-space source added to Vlasov's equation. The third quantity is the two-point correlation function of the incoherent part of the phase-space density which acts as a self-consistent source of quasiparticle and potential fluctuations. This theory explicitly takes into account the self-consistent nature of the electrostatic-field fluctuations which introduces new effects not found in the usual ''test-particle'' theories. Explicit equations for the fundamental quantities are derived in the direct interaction approximation. Special attention is paid to the two-point correlations and the relation to theories of phase-space granulation

  18. Quasiparticle pole strength in nuclear matter

    International Nuclear Information System (INIS)

    Poggioli, R.S.; Jackson, A.D.

    1975-01-01

    It is argued that single-particle-like behavior in nuclear matter is much less probable than Brueckner theory suggests. In particular, the quasiparticle pole strength is evaluated for nuclear matter and it is shown that, contrary to the spirit of Brueckner theory, low momentum states play a crucial role in determining the magnitude of z/sub k/sub F/. (auth)

  19. 16O+16O molecular nature of the superdeformed band of 32S and the evolution of the molecular structure

    International Nuclear Information System (INIS)

    Kimura, Masaaki; Horiuchi, Hisashi

    2004-01-01

    The relation between the superdeformed band of 32 S and 16 O+ 16 O molecular bands is studied by the deformed-basis antisymmetrized molecular dynamics with the Gogny D1S force. It is found that the obtained superdeformed band members of S have a considerable amount of the 16 O+ 16 O component. Above the superdeformed band, we have obtained two excited rotational bands which have more prominent character of the 16 O+ 16 O molecular band. These three rotational bands are regarded as a series of 16 O+ 16 O molecular bands which were predicted by using the unique 16 O- 16 O optical potential. As the excitation energy and principal quantum number of the relative motion increase, the 16 O+ 16 O cluster structure becomes more prominent but at the same time, the band members are fragmented into several states

  20. Valley-dependent band structure and valley polarization in periodically modulated graphene

    Science.gov (United States)

    Lu, Wei-Tao

    2016-08-01

    The valley-dependent energy band and transport property of graphene under a periodic magnetic-strained field are studied, where the time-reversal symmetry is broken and the valley degeneracy is lifted. The considered superlattice is composed of two different barriers, providing more degrees of freedom for engineering the electronic structure. The electrons near the K and K' valleys are dominated by different effective superlattices. It is found that the energy bands for both valleys are symmetric with respect to ky=-(AM+ξ AS) /4 under the symmetric superlattices. More finite-energy Dirac points, more prominent collimation behavior, and new crossing points are found for K' valley. The degenerate miniband near the K valley splits into two subminibands and produces a new band gap under the asymmetric superlattices. The velocity for the K' valley is greatly renormalized compared with the K valley, and so we can achieve a finite velocity for the K valley while the velocity for the K' valley is zero. Especially, the miniband and band gap could be manipulated independently, leading to an increase of the conductance. The characteristics of the band structure are reflected in the transmission spectra. The Dirac points and the crossing points appear as pronounced peaks in transmission. A remarkable valley polarization is obtained which is robust to the disorder and can be controlled by the strain, the period, and the voltage.

  1. High-order harmonic generation from a two-dimensional band structure

    Science.gov (United States)

    Jin, Jian-Zhao; Xiao, Xiang-Ru; Liang, Hao; Wang, Mu-Xue; Chen, Si-Ge; Gong, Qihuang; Peng, Liang-You

    2018-04-01

    In the past few years, harmonic generation in solids has attracted tremendous attention. Recently, some experiments of two-dimensional (2D) monolayer or few-layer materials have been carried out. These studies demonstrated that harmonic generation in the 2D case shows a strong dependence on the laser's orientation and ellipticity, which calls for a quantitative theoretical interpretation. In this work, we carry out a systematic study on the harmonic generation from a 2D band structure based on a numerical solution to the time-dependent Schrödinger equation. By comparing with the 1D case, we find that the generation dynamics can have a significant difference due to the existence of many crossing points in the 2D band structure. In particular, the higher conduction bands can be excited step by step via these crossing points and the total contribution of the harmonic is given by the mixing of transitions between different clusters of conduction bands to the valence band. We also present the orientation dependence of the harmonic yield on the laser polarization direction.

  2. 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.

  3. Photonic Band Structure of Dispersive Metamaterials Formulated as a Hermitian Eigenvalue Problem

    KAUST Repository

    Raman, Aaswath; Fan, Shanhui

    2010-01-01

    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.

  4. 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.

  5. Monolithic dual-band HgCdTe infrared detector structure

    CSIR Research Space (South Africa)

    Parish, G

    1997-07-01

    Full Text Available A monolithic HgCdTe photoconductive device structure is presented that is suitable for dual-band optically registered infrared photodetection in the two atmospheric transmission windows of 3-5 mu m and 8-12 mu m, which correspond to the mid...

  6. Two-band tariff for domestic use: Italian Electricity Board rate structure

    International Nuclear Information System (INIS)

    Barteselli, R.

    1992-01-01

    ENEL (the Italian National Electricity Board) has begun to introduce a new rate structure for households: the 'two-band tariff'. This article is an effort to examine in principle how the new tariff could optimize load management when applied to the whole household sector

  7. The transfer to technology to manufacture the disk of X-band accelerator structure

    International Nuclear Information System (INIS)

    Ueno, Kenji; Kawamata, Hiroshi; Takatomi, Toshikazu; Kume, Tatsuya; Funahashi, Yoshisato

    2005-01-01

    We research the transfer of manufacturing technology on X-band structure disks. From this issue we confirm that the venders will be able to manufacture disks when they get the process sheet method and drawings. More it is clear that we have to consider the automation process in order to get the repeatability of the disks. (author)

  8. The Electronic Band Structure of Platinum Oxide (PtO) | Omehe ...

    African Journals Online (AJOL)

    We have performed the electronic band structure of the bulk and monolayer of PtO using the full potential linear muffin-tin orbital and the projector augmented wave method with the density functional theory. We applied the LDA and LDA+U scheme to both methods. It was found out that the LDA calculation of bulk PtO ...

  9. 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 to ...

  10. 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...

  11. Using Quasiparticle Poisoning To Detect Photons

    Science.gov (United States)

    Echternach, Pierre; Day, Peter

    2006-01-01

    According to a proposal, a phenomenon associated with excitation of quasiparticles in certain superconducting quantum devices would be exploited as a means of detecting photons with exquisite sensitivity. The phenomenon could also be exploited to perform medium-resolution spectroscopy. The proposal was inspired by the observation that Coulomb blockade devices upon which some quantum logic gates are based are extremely sensitive to quasiparticles excited above the superconducting gaps in their leads. The presence of quasiparticles in the leads can be easily detected via the charge states. If quasiparticles could be generated in the leads by absorption of photons, then the devices could be used as very sensitive detectors of electromagnetic radiation over the spectral range from x-rays to submillimeter waves. The devices in question are single-Cooper-pair boxes (SCBs), which are mesoscopic superconducting devices developed for quantum computing. An SCB consists of a small superconducting island connected to a reservoir via a small tunnel junction and connected to a voltage source through a gate capacitor. An SCB is an artificial two-level quantum system, the Hamiltonian of which can be controlled by the gate voltage. One measures the expected value of the charge of the eigenvectors of this quantum system by use of a radio-frequency single-electron transistor. A plot of this expected value of charge as a function of gate voltage resembles a staircase that, in the ideal case, consists of steps of height 2 e (where e is the charge of one electron). Experiments have shown that depending on the parameters of the device, quasiparticles in the form of "broken" Cooper pairs present in the reservoir can tunnel to the island, giving rise to steps of 1 e. This effect is sometimes called "poisoning." Simulations have shown that an extremely small average number of quasiparticles can generate a 1-e periodic signal. In a device according to the proposal, this poisoning would be

  12. The effect of exchange interaction on quasiparticle Landau levels in narrow-gap quantum well heterostructures.

    Science.gov (United States)

    Krishtopenko, S S; Gavrilenko, V I; Goiran, M

    2012-04-04

    Using the 'screened' Hartree-Fock approximation based on the eight-band k·p Hamiltonian, we have extended our previous work (Krishtopenko et al 2011 J. Phys.: Condens. Matter 23 385601) on exchange enhancement of the g-factor in narrow-gap quantum well heterostructures by calculating the exchange renormalization of quasiparticle energies, the density of states at the Fermi level and the quasiparticle g-factor for different Landau levels overlapping. We demonstrate that exchange interaction yields more pronounced Zeeman splitting of the density of states at the Fermi level and leads to the appearance of peak-shaped features in the dependence of the Landau level energies on the magnetic field at integer filling factors. We also find that the quasiparticle g-factor does not reach the maximum value at odd filling factors in the presence of large overlapping of spin-split Landau levels. We advance an argument that the behavior of the quasiparticle g-factor in weak magnetic fields is defined by a random potential of impurities in narrow-gap heterostructures. © 2012 IOP Publishing Ltd

  13. Observation of dark-current signals from the S-band structures of the SLAC linac

    International Nuclear Information System (INIS)

    Assmann, R.; Decker, F.J.; Seidel, M.; Siemann, R.H.; Whittum, D.

    1997-07-01

    It is well known that the electro-magnetic fields in high-gradient RF structures can cause electron emission from the metallic structure walls. If the emitted electrons are captured and accelerated by the accelerating fields so-called dark-current is induced. Dark-currents have been measured and studied for various RF-structures. In this paper the authors present measurements of RF induced signals for the SLC S-band structures. For nominal gradients of 17 MV/m it is shown that the dark-current can be strong enough to significantly reduce the signal-to-noise ratio of the SLC beam wire scanners. They also show results from RF measurements in the dipole band. The measurements are compared to more direct observations of dark-current and it is tried to connect the results to possible effects on the accelerated particle beam

  14. Results from the CLIC X-Band Structure Test Program at NLCTA

    International Nuclear Information System (INIS)

    Adolphsen, C.

    2009-01-01

    As part of a SLAC-CERN-KEK collaboration on high gradient X-band structure research, several prototype structures for the CLIC linear collider study have been tested using two of the high power (300 MW) X-band rf stations in the NLCTA facility at SLAC. These structures differ in terms of their fabrication (brazed disks and clamped quadrants), gradient profile (amount by which the gradient increases along the structure, which optimizes efficiency and maximizes sustainable gradient) and HOM damping (use of slots or waveguides to rapidly dissipate dipole mode energy). The CLIC goal in the next few years is to demonstrate the feasibility of a CLIC-ready baseline design and to investigate alternatives that could increase efficiency. This paper summarizes the high gradient test results from NLCTA in support of this effort.

  15. Microscopic model of quasiparticle wave packets in superfluids, superconductors, and paired Hall states.

    Science.gov (United States)

    Parameswaran, S A; Kivelson, S A; Shankar, R; Sondhi, S L; Spivak, B Z

    2012-12-07

    We study the structure of Bogoliubov quasiparticles, bogolons, the fermionic excitations of paired superfluids that arise from fermion (BCS) pairing, including neutral superfluids, superconductors, and paired quantum Hall states. The naive construction of a stationary quasiparticle in which the deformation of the pair field is neglected leads to a contradiction: it carries a net electrical current even though it does not move. However, treating the pair field self-consistently resolves this problem: in a neutral superfluid, a dipolar current pattern is associated with the quasiparticle for which the total current vanishes. When Maxwell electrodynamics is included, as appropriate to a superconductor, this pattern is confined over a penetration depth. For paired quantum Hall states of composite fermions, the Maxwell term is replaced by a Chern-Simons term, which leads to a dipolar charge distribution and consequently to a dipolar current pattern.

  16. Multi-quasiparticle high-K isomeric states in deformed nuclei

    Directory of Open Access Journals (Sweden)

    Xu F. R.

    2016-01-01

    Full Text Available In the past years, we have made many theoretical investigations on multi-quasiparticle high-K isomeric states. A deformation-pairing-configuration self-consistent calculation has been developed by calculating a configuration-constrained multi-quasiparticle potential energy surface (PES. The specific single-particle orbits that define the high-K configuration are identified and tracked (adiabatically blocked by calculating the average Nilsson numbers. The deformed Woods-Saxon potential was taken to give single-particle orbits. The configuration-constrained PES takes into account the shape polarization effect. Such calculations give good results on excitation energies, deformations and other structure information about multi-quasiparticle high-K isomeric states. Many different mass regions have been investigated.

  17. Optical properties and electronic band structure of AgInSe2

    International Nuclear Information System (INIS)

    Ozaki, Shunji; Adachi, Sadao

    2006-01-01

    Optical properties of a chalcopyrite semiconductor AgInSe 2 have been studied by optical absorption, spectroscopic ellipsometry (SE), and thermoreflectance (TR) measurements. The measurements reveal distinct structures at energies of the critical points in the Brillouin zone. By performing the band-structure calculation, these critical points have been successfully assigned to specific points in the Brillouin zone. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  18. Relativistic band-structure calculations for electronic properties of actinide dioxides

    International Nuclear Information System (INIS)

    Maehira, Takahiro; Hotta, Takashi

    2007-01-01

    Energy band structures of actinide dioxides AnO 2 (An=Th, U, Np, and Pu) are investigated by a relativistic linear augmented-plane-wave method with the exchange-correlation potential in a local density approximation (LDA). It is found in common that the energy bands in the vicinity of the Fermi level are mainly due to the hybridization between actinide 5f and oxygen 2p electrons. By focusing on the crystalline electric field states, we point out the problem in the application of the LDA to AnO 2

  19. Tuning the band structure of graphene nanoribbons through defect-interaction-driven edge patterning

    Science.gov (United States)

    Du, Lin; Nguyen, Tam N.; Gilman, Ari; Muniz, André R.; Maroudas, Dimitrios

    2017-12-01

    We report a systematic analysis of pore-edge interactions in graphene nanoribbons (GNRs) and their outcomes based on first-principles calculations and classical molecular-dynamics simulations. We find a strong attractive interaction between nanopores and GNR edges that drives the pores to migrate toward and coalesce with the GNR edges, which can be exploited to form GNR edge patterns that impact the GNR electronic band structure and tune the GNR band gap. Our analysis introduces a viable physical processing strategy for modifying GNR properties by combining defect engineering and thermal annealing.

  20. Bose-Einstein condensates in optical lattices: Band-gap structure and solitons

    International Nuclear Information System (INIS)

    Louis, Pearl J. Y.; Kivshar, Yuri S.; Ostrovskaya, Elena A.; Savage, Craig M.

    2003-01-01

    We analyze the existence and stability of spatially extended (Bloch-type) and localized states of a Bose-Einstein condensate loaded into an optical lattice. In the framework of the Gross-Pitaevskii equation with a periodic potential, we study the band-gap structure of the matter-wave spectrum in both the linear and nonlinear regimes. We demonstrate the existence of families of spatially localized matter-wave gap solitons, and analyze their stability in different band gaps, for both repulsive and attractive atomic interactions

  1. 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.

  2. Metal-induced gap states in ferroelectric capacitors and its relationship with complex band structures

    Science.gov (United States)

    Junquera, Javier; Aguado-Puente, Pablo

    2013-03-01

    At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials. Financial support provided by MICINN Grant FIS2009-12721-C04-02, and by the European Union Grant No. CP-FP 228989-2 ``OxIDes''. Computer resources provided by the RES.

  3. Crystal structure and energy band and optical properties of phosphate Sr3P4O13

    International Nuclear Information System (INIS)

    Zhang, Y.-C.; Cheng, W.-D.; Wu, D.-S.; Zhang, H.; Chen, D.-G.; Gong, Y.-J.; Kan, Z.-G.

    2004-01-01

    A single crystal of the compound Sr 3 P 4 O 13 has been found and the crystal structure has been characterized by means of single crystal X-ray diffraction analysis. The compound crystallizes in triclinic system and belongs to space group P1-bar. It builds up from SrO 7 polyhedra and P 4 O 13 -6 anions and has a layered structure, and the Sr atoms are located in the interlayer space. The absorption and luminescence spectrum of Sr 3 P 4 O 13 microcrystals have been measured. The calculated results of crystal energy band structure by the DFT show that the solid state of Sr 3 P 4 O 13 is an isolator with direct band gap. The calculated total and partial density of states indicate that the top valence bands are contributions from P 3p and O 2p states and low conduction bands mostly originate from Sr atomic states. The calculated optical response functions expect that the Sr 3 P 4 O 13 is a low refractive index, and it is possible that the Sr 3 P 4 O 13 is used to make transparent material between the UV and FR light zone

  4. Electronic band structures and optical properties of type-II superlattice photodetectors with interfacial effect.

    Science.gov (United States)

    Qiao, Peng-Fei; Mou, Shin; Chuang, Shun Lien

    2012-01-30

    The electronic band structures and optical properties of type-II superlattice (T2SL) photodetectors in the mid-infrared (IR) range are investigated. We formulate a rigorous band structure model using the 8-band k · p method to include the conduction and valence band mixing. After solving the 8 × 8 Hamiltonian and deriving explicitly the new momentum matrix elements in terms of envelope functions, optical transition rates are obtained through the Fermi's golden rule under various doping and injection conditions. Optical measurements on T2SL photodetectors are compared with our model and show good agreement. Our modeling results of quantum structures connect directly to the device-level design and simulation. The predicted doping effect is readily applicable to the optimization of photodetectors. We further include interfacial (IF) layers to study the significance of their effect. Optical properties of T2SLs are expected to have a large tunable range by controlling the thickness and material composition of the IF layers. Our model provides an efficient tool for the designs of novel photodetectors.

  5. Electronic structures and valence band splittings of transition metals doped GaNs

    International Nuclear Information System (INIS)

    Lee, Seung-Cheol; Lee, Kwang-Ryeol; Lee, Kyu-Hwan

    2007-01-01

    For a practical viewpoint, presence of spin splitting of valence band in host semiconductors by the doping of transition metal (TM) ions is an essential property when designing a diluted magnetic semiconductors (DMS) material. The first principle calculations were performed on the electronic and magnetic structure of 3d transition metal doped GaN. V, Cr, and Mn doped GaNs could not be candidates for DMS materials since most of their magnetic moments is concentrated on the TM ions and the splittings of valence band were negligible. In the cases of Fe, Co, Ni, and Cu doped GaNs, on the contrary, long-ranged spin splitting of valence band was found, which could be candidates for DMS materials

  6. Band structures of two dimensional solid/air hierarchical phononic crystals

    International Nuclear Information System (INIS)

    Xu, Y.L.; Tian, X.G.; Chen, C.Q.

    2012-01-01

    The hierarchical phononic crystals to be considered show a two-order “hierarchical” feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.

  7. Band structures of two dimensional solid/air hierarchical phononic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Y.L.; Tian, X.G. [State Key Laboratory for Mechanical Structure Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Chen, C.Q., E-mail: chencq@tsinghua.edu.cn [Department of Engineering Mechanics, AML and CNMM, Tsinghua University, Beijing 100084 (China)

    2012-06-15

    The hierarchical phononic crystals to be considered show a two-order 'hierarchical' feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.

  8. 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.

  9. 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...

  10. Engineered band structure for an enhanced performance on quantum dot-sensitized solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Bin Bin [Key Laboratory of Macromolecular Science of Shaanxi Province and School of Materials Science and Engineering, Shaanxi Normal University, Xi' an 710062 (China); Department of Chemical Engineering, Institute of Chemical Industry, Shaanxi Institute of Technology, Xi' an 710300 (China); Wang, Ye Feng [School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi' an 710062 (China); Wei, Dong; Chen, Yu; Zeng, Jing Hui, E-mail: jhzeng@ustc.edu [Key Laboratory of Macromolecular Science of Shaanxi Province and School of Materials Science and Engineering, Shaanxi Normal University, Xi' an 710062 (China); Cui, Bin [School of Chemistry and Materials Science, Northwestern University, Xi' an 710620 (China)

    2016-06-20

    A photon-to-current efficiency of 2.93% is received for the Mn-doped CdS (MCdS)-quantum dot sensitized solar cells (QDSSCs) using Mn:ZnO (MZnO) nanowire as photoanode. Hydrothermal synthesized MZnO are spin-coated on fluorine doped tin oxide (FTO) glass with P25 paste to serve as photoanode after calcinations. MCdS was deposited on the MZnO film by the successive ionic layer adsorption and reaction method. The long lived excitation energy state of Mn{sup 2+} is located inside the conduction band in the wide bandgap ZnO and under the conduction band of CdS, which increases the energetic overlap of donor and acceptor states, reducing the “loss-in-potential,” inhibiting charge recombination, and accelerating electron injection. The engineered band structure is well reflected by the electrochemical band detected using cyclic voltammetry. Cell performances are evidenced by current density-voltage (J-V) traces, diffuse reflectance spectra, transient PL spectroscopy, and incident photon to current conversion efficiency characterizations. Further coating of CdSe on MZnO/MCdS electrode expands the light absorption band of the sensitizer, an efficiency of 4.94% is received for QDSSCs.

  11. Effect of initial structure on strengthening and properties of the 35NKhTYu alloy bands

    International Nuclear Information System (INIS)

    Vorontsov, N.M.; Shugaenko, V.K.; Drapiko, P.E.; Chernyakova, L.E.; Patseka, R.F.

    1978-01-01

    Variation in the structure, mechanical strength, plasticity, and elasticity of thin (about 0.15 mm thick) bands of 36NKhTYu alloy after their cold rolling to the reduction degree up to 70% was examined. The influence of the cold plastic deformation on the dislocation structure of the alloy has been determined. By resorting to the method of transmission electron microscopy, the distribution of dislocations depending on the reduction degree has been shown. The character of the influence of the initial structure of bands after their plastic deformation on the process of decomposition of the solid solution and the formation of γ 1 -phase in tempering and a variation in the mechanical properties of 36NKhTYu alloy have been established

  12. Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals

    International Nuclear Information System (INIS)

    Xu, Zhenlong; Wu, Fugen; Guo, Zhongning

    2012-01-01

    The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies. -- Highlights: ► We report a new class of quasi-periodic hetero-structures, arc-shaped phononic crystals (APCs). ► The results show the first PBGs start with zero Hz with low modes. ► Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials.

  13. 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.

    2016-01-01

    Electron pitch angle (D (alpha)) and momentum (D(pp)) 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 (alpha) 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 D alpha 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 D alpha coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than D alpha coefficients for the case n does not = 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of D alpha 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 deg and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle

  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.

    2016-01-01

    Electron pitch angle (D(sub (alpha alpha))) and momentum (D(sub pp)) 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 less than or equal to 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 (alpha) 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 D(sub alpha alpha) and D(sub pp) 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 D(sub pp) diffusion coefficient for ECH waves is one to two orders smaller than D(sub alpha alpha) coefficients. For chorus waves, D(sub pp) coefficients are about an order of magnitude smaller than D(sub alpha alpha) coefficients for the case n does not equal 0. In case of Landau resonance, the values of D(sub pp) coefficient are generally larger than the values of D(sub alpha alpha) 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 deg and harmonic resonances

  15. Electronic structures and band gaps of chains and sheets based on phenylacetylene units

    International Nuclear Information System (INIS)

    Kondo, Masakazu; Nozaki, Daijiro; Tachibana, Masamitsu; Yumura, Takashi; Yoshizawa, Kazunari

    2005-01-01

    We investigate the electronic structures of polymers composed of π-conjugated phenylacetylene (PA) units, m-PA-based and p-PA-based wires, at the extended Hueckel level of theory. It is demonstrated that these conjugated systems should have a variety of electric conductance. All of the one-dimensional (1D) chains and the two-dimensional (2D) sheet based on the m-PA unit are insulators with large band gaps of 2.56 eV because there is no effective orbital interaction with neighboring chains. On the other hand, p-PA-based 1D chains have relatively small band gaps that decrease with an increase in chain width (1.17-1.74 eV) and are semiconductive. The p-PA-based sheet called 'graphyne', a 2D-limit of the p-PA-based 1D chains, shows a small band gap of 0.89 eV. The variety of band electronic structures is discussed in terms of frontier crystal orbitals

  16. Structure of collective bands and deformations in 74,76Kr

    International Nuclear Information System (INIS)

    Tripathy, K.C.; Sahu, R.

    2000-01-01

    The structure of collective bands in 74,76 Kr is studied within the framework of the deformed configuration mixing shell model based on Hartree-Fock states. The active single-particle orbits are 1p 3/2 , 0f 5/2 , 1p 1/2 and 0g 9/2 with 56 Ni as the inert core. A modified Kuo interaction has been used for the above configuration space. The 74 Kr nucleus is found to be the most deformed nucleus among the krypton isotopes which is in agreement with experiment. The deformation is found to decrease for the 76 Kr isotope. The calculated positive- and negative-parity bands agree quite well with the experiment for both the nuclei. A number of excited bands is also predicted. We have also calculated B(E2) values and compared them with available experimental data. The structure of the strongly coupled band built on K = 4 (+) in 76 Kr is also studied. (author)

  17. Complex band structures of transition metal dichalcogenide monolayers with spin–orbit coupling effects

    International Nuclear Information System (INIS)

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-01-01

    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. (paper)

  18. 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.

  19. Band structures of phononic crystal composed of lattices with different periodic constants

    International Nuclear Information System (INIS)

    Hu, Jia-Guang; Xu, Wen

    2014-01-01

    With a square lattice mercury and water system being as the model, the band structures of nesting and compound phononic crystals with two different lattice constants were investigated using the method of the supercell plane wave expansion. It was observed that large band gaps can be achieved in low frequency regions by adjusting one of the lattice constants. Meanwhile, effects similar to interstitial impurity defects can be achieved with the increase of lattice constant of the phononic crystal. The corresponding defect modes can be stimulated in band gaps. The larger the lattice constant, the stronger the localization effect of defect modes on the wave. In addition, the change of the filling fraction of impurity exerts great influence on the frequency and localization of defect modes. Furthermore, the change of the position of impurity has notable influence on the frequency of defect modes and their localization. However, the geometry structure and orientation of impurity have little effect on the frequency of defect modes and their localization in the band gap.

  20. Field induced spontaneous quasiparticle decay and renormalization of quasiparticle dispersion in a quantum antiferromagnet.

    Science.gov (United States)

    Hong, Tao; Qiu, Y; Matsumoto, M; Tennant, D A; Coester, K; Schmidt, K P; Awwadi, F F; Turnbull, M M; Agrawal, H; Chernyshev, A L

    2017-05-05

    The notion of a quasiparticle, such as a phonon, a roton or a magnon, is used in modern condensed matter physics to describe an elementary collective excitation. The intrinsic zero-temperature magnon damping in quantum spin systems can be driven by the interaction of the one-magnon states and multi-magnon continuum. However, detailed experimental studies on this quantum many-body effect induced by an applied magnetic field are rare. Here we present a high-resolution neutron scattering study in high fields on an S=1/2 antiferromagnet C 9 H 18 N 2 CuBr 4 . Compared with the non-interacting linear spin-wave theory, our results demonstrate a variety of phenomena including field-induced renormalization of one-magnon dispersion, spontaneous magnon decay observed via intrinsic linewidth broadening, unusual non-Lorentzian two-peak structure in the excitation spectra and a dramatic shift of spectral weight from one-magnon state to the two-magnon continuum.

  1. Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

    International Nuclear Information System (INIS)

    Jungwirth, T.; Novak, V.; Cukr, M.; Zemek, J.; Marti, X.; Horodyska, P.; Nemec, P.; Holy, V.; Maca, F.; Shick, A. B.; Masek, J.; Kuzel, P.; Nemec, I.; Gallagher, B. L.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.

    2011-01-01

    Our ab initio theory calculations predict a semiconducting band structure of I-Mn-V compounds. We demonstrate on LiMnAs that high-quality materials with group-I alkali metals in the crystal structure can be grown by molecular beam epitaxy. Optical measurements on the LiMnAs epilayers are consistent with the theoretical electronic structure. Our calculations also reproduce earlier reports of high antiferromagnetic ordering temperature and predict large, spin-orbit-coupling-induced magnetic anisotropy effects. We propose a strategy for employing antiferromagnetic semiconductors in high-temperature semiconductor spintronics.

  2. Autopsy on an RF-Processed X-band Travelling Wave Structure

    International Nuclear Information System (INIS)

    Le Pimpec, Frederic

    2002-01-01

    In an effort to locate the cause(s) of high electric-field breakdown in x-band accelerating structures, we have cleanly-autopsied (no debris added by post-operation structure disassembly) an RF-processed structure. Macroscopic localization provided operationally by RF reflected wave analysis and acoustic sensor pickup was used to connect breakdowns to autopsied crater damage areas. Surprisingly, the microscopic analyses showed breakdown craters in areas of low electric field. High currents induced by the magnetic field on sharp corners of the input coupler appears responsible for the extreme breakdown damage observed

  3. SLAC High Gradient Testing of a KEK X-Band Accelerator Structure

    International Nuclear Information System (INIS)

    Loewen, Rod

    2000-01-01

    The high accelerating gradients required for future linear colliders demands a better study of field emission and RF breakdown in accelerator structures. Changes in structure geometry, vacuum pumping, fabrication methods, and surface finish can all potentially impact the conditioning process, dark current emission, and peak RF power handling capability. Recent tests at SLAC of KEK's ''M2'' travelling wave x-band accelerator section provides an opportunity to investigate some of these effects by comparing its performance to previously high power tested structures at SLAC. In addition to studying ultimate power limitations, this test also demonstrates the use of computer automated conditioning to reach practical, achievable gradients

  4. Experimental Studies of W-Band Accelerator Structures at High Field

    Energy Technology Data Exchange (ETDEWEB)

    Hill, Marc E

    2001-02-09

    A high-gradient electron accelerator is desired for high-energy physics research, where frequency scalings of breakdown and trapping of itinerant beamline particles dictates operation of the accelerator at short wavelengths. The first results of design and test of a high-gradient mm-wave linac with an operating frequency at 91.392 GHz (W-band) are presented. A novel approach to particle acceleration is presented employing a planar, dielectric lined waveguide used for particle acceleration. The traveling wave fields in the planar dielectric accelerator (PDA) are analyzed for an idealized structure, along with a circuit equivalent model used for understanding the structure as a microwave circuit. Along with the W-band accelerator structures, other components designed and tested are high power rf windows, high power attenuators, and a high power squeeze-type phase shifter. The design of the accelerator and its components where eased with the aide of numerical simulations using a finite-difference electromagnetic field solver. Manufacturing considerations of the small, delicate mm-wave components and the steps taken to reach a robust fabrication process are detailed. These devices were characterized under low power using a two-port vector network analyzer to verify tune and match, including measurements of the structures' fields using a bead-pull. The measurements are compared with theory throughout. Addition studies of the W-band structures were performed under high power utilizing a 11.424 GHz electron linac as a current source. Test results include W-band power levels of 200 kW, corresponding to fields in the PDA of over 20 MV/m, a higher gradient than any collider. Planar accelerator devices naturally have an rf quadrupole component of the accelerating field. Presented for the first time are the measurements of this effect.

  5. Decay patterns of multi-quasiparticle bands—a model independent test of chiral symmetry

    International Nuclear Information System (INIS)

    Lawrie, E A

    2017-01-01

    Nuclear chiral systems exhibit chiral symmetry bands, built on left-handed and right-handed angular momentum nucleon configurations. The experimental search for such chiral systems revealed a number of suitable candidates, however an unambiguous identification of nuclear chiral symmetry is still outstanding. In this work it is shown that the decay patterns of chiral bands built on multi-quasiparticle configurations are different from those involving different single-particle configurations. It is suggested to use the observed decay patterns of chiral candidates as a new model-independent test of chiral symmetry. (paper)

  6. Geometrical Description of fractional quantum Hall quasiparticles

    Science.gov (United States)

    Park, Yeje; Yang, Bo; Haldane, F. D. M.

    2012-02-01

    We examine a description of fractional quantum Hall quasiparticles and quasiholes suggested by a recent geometrical approach (F. D. M. Haldane, Phys. Rev. Lett. 108, 116801 (2011)) to FQH systems, where the local excess electric charge density in the incompressible state is given by a topologically-quantized ``guiding-center spin'' times the Gaussian curvature of a ``guiding-center metric tensor'' that characterizes the local shape of the correlation hole around electrons in the fluid. We use a phenomenological energy function with two ingredients: the shear distortion energy of area-preserving distortions of the fluid, and a local (short-range) approximation to the Coulomb energy of the fluctuation of charge density associated with the Gaussian curvature. Quasiparticles and quasiholes of the 1/3 Laughlin state are modeled as ``punctures'' in the incompressible fluid which then relax by geometric distortion which generates Gaussian curvature, giving rise to the charge-density profile around the topological excitation.

  7. Quasi-Particle Relaxation and Quantum Femtosecond Magnetism in Non-Equilibrium Phases of Insulating Manganites

    Science.gov (United States)

    Perakis, Ilias; Kapetanakis, Myron; Lingos, Panagiotis; Barmparis, George; Patz, A.; Li, T.; Wang, Jigang

    We study the role of spin quantum fluctuations driven by photoelectrons during 100fs photo-excitation of colossal magneto-resistive manganites in anti-ferromagnetic (AFM) charge-ordered insulating states with Jahn-Teller distortions. Our mean-field calculation of composite fermion excitations demonstrates that spin fluctuations reduce the energy gap by quasi-instantaneously deforming the AFM background, thus opening a conductive electronic pathway via FM correlation. We obtain two quasi-particle bands with distinct spin-charge dynamics and dependence on lattice distortions. To connect with fs-resolved spectroscopy experiments, we note the emergence of fs magnetization in the low-temperature magneto-optical signal, with threshold dependence on laser intensity characteristic of a photo-induced phase transition. Simultaneously, the differential reflectivity shows bi-exponential relaxation, with fs component, small at low intensity, exceeding ps component above threshold for fs AFM-to-FM switching. This suggests the emergence of a non-equilibrium metallic FM phase prior to establishment of a new lattice structure, linked with quantum magnetism via spin/charge/lattice couplings for weak magnetic fields.

  8. First-principles study on band structures and electrical transports of doped-SnTe

    Directory of Open Access Journals (Sweden)

    Xiao Dong

    2016-06-01

    Full Text Available Tin telluride is a thermoelectric material that enables the conversion of thermal energy to electricity. SnTe demonstrates a great potential for large-scale applications due to its lead-free nature and the similar crystal structure to PbTe. In this paper, the effect of dopants (i.e., Mg, Ca, Sr, Ba, Eu, Yb, Zn, Cd, Hg, and In on the band structures and electrical transport properties of SnTe was investigated based on the first-principles density functional theory including spin–orbit coupling. The results show that Zn and Cd have a dominant effect of band convergence, leading to power factor enhancement. Indium induces obvious resonant states, while Hg-doped SnTe exhibits a different behavior with defect states locating slightly above the Fermi level.

  9. Valence band structures of InAs/GaAs quantum rings using the Fourier transform method

    International Nuclear Information System (INIS)

    Jia Boyong; Yu Zhongyuan; Liu Yumin

    2009-01-01

    The valence band structures of strained InAs/GaAs quantum rings are calculated, with the four-band k · p model, in the framework of effective-mass envelope function theory. When determining the Hamiltonian matrix elements, we develop the Fourier transform method instead of the widely used analytical integral method. Using Fourier transform, we have investigated the energy levels as functions of the geometrical parameters of the rings and compared our results with those obtained by the analytical integral method. The results show that the energy levels in the quantum rings change dramatically with the inner radius, outer radius, average radius, width, height of the ring and the distance between two adjacent rings. Our method can be adopted in low-dimensional structures with arbitrary shape. Our results are consistent with those in the literature and should be helpful for studying and fabricating optoelectronic devices

  10. Optical properties of Nb and Mo calculated from augmented-plane-wave band structures

    International Nuclear Information System (INIS)

    Pickett, W.E.; Allen, P.B.

    1975-01-01

    Nonrelativistic band calculations of Mattheiss for Nb and Petroff and Viswanathan for Mo are used to calculate the imaginary part epsilon 2 of the dielectric function for these metals. The structure resulting from interband transitions in the frequency range 0.1--0.5 Ry is found to give fairly good agreement with experiment. The calculation indicates that structure in epsilon 2 can arise from transitions away from symmetry points and lines in the Brillouin zone. The difficulty in distinguishing between the direct and indirect transition models for epsilon 2 is shown to arise from a lack of strong optical critical points. Predictions of the rigid-band model for the optical properties of Nb-Mo alloys are presented

  11. A first principle study of band structure of III-nitride compounds

    Energy Technology Data Exchange (ETDEWEB)

    Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

    2005-12-15

    The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

  12. Photonic band structures solved by a plane-wave-based transfer-matrix method.

    Science.gov (United States)

    Li, Zhi-Yuan; Lin, Lan-Lan

    2003-04-01

    Transfer-matrix methods adopting a plane-wave basis have been routinely used to calculate the scattering of electromagnetic waves by general multilayer gratings and photonic crystal slabs. In this paper we show that this technique, when combined with Bloch's theorem, can be extended to solve the photonic band structure for 2D and 3D photonic crystal structures. Three different eigensolution schemes to solve the traditional band diagrams along high-symmetry lines in the first Brillouin zone of the crystal are discussed. Optimal rules for the Fourier expansion over the dielectric function and electromagnetic fields with discontinuities occurring at the boundary of different material domains have been employed to accelerate the convergence of numerical computation. Application of this method to an important class of 3D layer-by-layer photonic crystals reveals the superior convergency of this different approach over the conventional plane-wave expansion method.

  13. Photonic band structures solved by a plane-wave-based transfer-matrix method

    International Nuclear Information System (INIS)

    Li Zhiyuan; Lin Lanlan

    2003-01-01

    Transfer-matrix methods adopting a plane-wave basis have been routinely used to calculate the scattering of electromagnetic waves by general multilayer gratings and photonic crystal slabs. In this paper we show that this technique, when combined with Bloch's theorem, can be extended to solve the photonic band structure for 2D and 3D photonic crystal structures. Three different eigensolution schemes to solve the traditional band diagrams along high-symmetry lines in the first Brillouin zone of the crystal are discussed. Optimal rules for the Fourier expansion over the dielectric function and electromagnetic fields with discontinuities occurring at the boundary of different material domains have been employed to accelerate the convergence of numerical computation. Application of this method to an important class of 3D layer-by-layer photonic crystals reveals the superior convergency of this different approach over the conventional plane-wave expansion method

  14. Harnessing the bistable composite shells to design a tunable phononic band gap structure

    Science.gov (United States)

    Li, Yi; Xu, Yanlong

    2018-02-01

    By proposing a system composed of an array of bistable composite shells immersed in air, we develop a new class of periodic structure to control the propagation of sound. Through numerical investigation, we find that the acoustic band gap of this system can be switched on and off by triggering the snap through deformation of the bistable composite shells. The shape of cross section and filling fraction of unit cell can be altered by different number of bistable composite shells, and they have strong impact on the position and width of the band gap. The proposed concept paves the way of using the bistable structures to design a new class of metamaterials that can be enable to manipulate sound.

  15. Measurements of higher order modes in a 30 cm long X-band structure

    International Nuclear Information System (INIS)

    Xiao, L.; Liang, Y.; Tong, D.; Zhang, H.

    2001-01-01

    The use of a cage of metallic wires as a bead is proposed to measure the higher order modes (HOMs) in an X-band accelerating structure. These long thin wires can isolate the longitudinal electric field component from other field components and produce sufficient frequency shift in bead-pull measurements. In the setup described in this paper, the bead is made by sputtering silver film onto a thin nylon line through a specially designed fixture. The cage has a size of approximately 0.5 mm in diameter, 2 mm in length and more than six metallic wires of less than 0.1 mm in width. The fabrication and calibration of the cage are described. The longitudinal electric fields of the lowest passband dipole mode TM 110 in a 30 cm long X-band structure are measured by bead-pull measurements. Results are compared with the calculated ones obtained from URMELT-code

  16. Tight binding electronic band structure calculation of achiral boron nitride single wall nanotubes

    International Nuclear Information System (INIS)

    Saxena, Prapti; Sanyal, Sankar P

    2006-01-01

    In this paper we report the Tight-Binding method, for the electronic structure calculations of achiral single wall Boron Nitride nanotubes. We have used the contribution of π electron only to define the electronic band structure for the solid. The Zone-folding method is used for the Brillouin Zone definition. Calculation of tight binding model parameters is done by fitting them to available experimental results of two-dimensional hexagonal monolayers of Boron Nitride. It has been found that all the boron nitride nanotubes (both zigzag and armchair) are constant gap semiconductors with a band gap of 5.27eV. All zigzag BNNTs are found to be direct gap semiconductors while all armchair nanotubes are indirect gap semiconductors. (author)

  17. Quasiparticle Interference on Cubic Perovskite Oxide Surfaces.

    Science.gov (United States)

    Okada, Yoshinori; Shiau, Shiue-Yuan; Chang, Tay-Rong; Chang, Guoqing; Kobayashi, Masaki; Shimizu, Ryota; Jeng, Horng-Tay; Shiraki, Susumu; Kumigashira, Hiroshi; Bansil, Arun; Lin, Hsin; Hitosugi, Taro

    2017-08-25

    We report the observation of coherent surface states on cubic perovskite oxide SrVO_{3}(001) thin films through spectroscopic-imaging scanning tunneling microscopy. A direct link between the observed quasiparticle interference patterns and the formation of a d_{xy}-derived surface state is supported by first-principles calculations. We show that the apical oxygens on the topmost VO_{2} plane play a critical role in controlling the coherent surface state via modulating orbital state.

  18. Number conserving approach in quasiparticle representation

    International Nuclear Information System (INIS)

    Oudih, M.R.; Fellah, M.; Allal, N.H.

    2003-01-01

    An exact number conserving approach is formulated in the quasiparticle representation to show the effect of the particle-number projection on the ground and the first 0+ excited states. It is applied to the two-level pairing model, which allows an exact solution and a comparison to other approaches. The present method has proved to be an advantageous alternative as compared to the BCS and to the usual methods used to restore the particle number symmetry. (author)

  19. Long-range spin deformations around quasiparticles

    International Nuclear Information System (INIS)

    Godfrey, M.; Gunn, M.

    1989-01-01

    The quasi-particle formed by a hole in a Heisenberg antiferromagnet has an associated long-range spin distortion whose amplitude increases with the velocity of the hole. The authors show that the existence and properties of this distortion follow from simple classical arguments based on the long-wavelength equations of motion for the spin system. A similar long-range distortion is found in the quantum-mechanical problem of an electron exchange coupled to a Heisenberg antiferromagnet

  20. Electronic band structure and optical properties of antimony selenide under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Abhijit, B.K.; Jayaraman, Aditya; Molli, Muralikrishna, E-mail: muralikrishnamolli@sssihl.edu.in [Department of Physics, Sri Sathya Sai Institute of Higher Learning, Prasanthinilayam, 515 134 (India)

    2016-05-23

    In this work we present the optical properties of Antimony Selenide (Sb{sub 2}Se{sub 3}) under ambient conditions and under pressure of 9.2 GPa obtained using first principles calculations. We investigated the electronic band structure using the FP-LAPW method within the sphere of the density functional theory. Optical properties like refractive index, absorption coefficient and optical conductivity are calculated using the WIEN2k code.

  1. Electronic band structure of TiFese2 in ferromagnetic phase

    International Nuclear Information System (INIS)

    Jahangirli, Z.A.; Mimura, K.; Shim, Y.; Mamedov, N.T.; Wakita, K.; Orudzhev, G.S.; Jahangirli, Z.A.

    2011-01-01

    Electronic band structure of crystalline TiFeSe 2 has been calculated using full-potential method of Linear Augmented Plane Wave (LAPW) in density-functional approach with exchange-correlation potential taken in Generalized Gradient Approximation (GGA). The chemical bond in TiFeSe 2 is shown to be metallic because energies of 3d-electrons localized at iron atoms are close to Fermi energy level

  2. Three-dimensional ordered particulate structures: Method to retrieve characteristics from photonic band gap data

    Science.gov (United States)

    Miskevich, Alexander A.; Loiko, Valery A.

    2015-01-01

    A method to retrieve characteristics of ordered particulate structures, such as photonic crystals, is proposed. It is based on the solution of the inverse problem using data on the photonic band gap (PBG). The quasicrystalline approximation (QCA) of the theory of multiple scattering of waves and the transfer matrix method (TMM) are used. Retrieval of the refractive index of particles is demonstrated. Refractive indices of the artificial opal particles are estimated using the published experimental data.

  3. Self-consistent field variational cellular method as applied to the band structure calculation of sodium

    International Nuclear Information System (INIS)

    Lino, A.T.; Takahashi, E.K.; Leite, J.R.; Ferraz, A.C.

    1988-01-01

    The band structure of metallic sodium is calculated, using for the first time the self-consistent field variational cellular method. In order to implement the self-consistency in the variational cellular theory, the crystal electronic charge density was calculated within the muffin-tin approximation. The comparison between our results and those derived from other calculations leads to the conclusion that the proposed self-consistent version of the variational cellular method is fast and accurate. (author) [pt

  4. Electronic structure of the misfit layer compound (SnS)(1.20)TiS2 : Band structure calculations and photoelectron spectra

    NARCIS (Netherlands)

    Fang, CM; deGroot, RA; Wiegers, GA; Haas, C

    1996-01-01

    In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)(1.20)TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar

  5. Electronic structure of the misfit layer compound (SnS)1.20TiS2 : band structure calculations and photoelectron spectra

    NARCIS (Netherlands)

    Fang, C.M.; Groot, R.A. de; Wiegers, G.A.; Haas, C.

    1996-01-01

    In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)1.20TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar

  6. Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

    Science.gov (United States)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

    2015-04-01

    High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

  7. Efficient evaluation of epitaxial MoS2 on sapphire by direct band structure imaging

    Science.gov (United States)

    Kim, Hokwon; Dumcenco, Dumitru; Fregnaux, Mathieu; Benayad, Anass; Kung, Yen-Cheng; Kis, Andras; Renault, Olivier; Lanes Group, Epfl Team; Leti, Cea Team

    The electronic band structure evaluation of two-dimensional metal dichalcogenides is critical as the band structure can be greatly influenced by the film thickness, strain, and substrate. Here, we performed a direct measurement of the band structure of as-grown monolayer MoS2 on single crystalline sapphire by reciprocal-space photoelectron emission microscopy with a conventional laboratory ultra-violet He I light source. Arrays of gold electrodes were deposited onto the sample in order to avoid charging effects due to the insulating substrate. This allowed the high resolution mapping (ΔE = 0.2 eV Δk = 0.05 Å-1) of the valence states in momentum space down to 7 eV below the Fermi level. The high degree of the epitaxial alignment of the single crystalline MoS2 nuclei was verified by the direct momentum space imaging over a large area containing multiple nuclei. The derived values of the hole effective mass were 2.41 +/-0.05 m0 and 0.81 +/-0.05 m0, respectively at Γ and K points, consistent with the theoretical values of the freestanding monolayer MoS2 reported in the literature. HK acknowledges the french CEA Basic Technological Research program (RTB) for funding.

  8. Lateral energy band profile modulation in tunnel field effect transistors based on gate structure engineering

    Directory of Open Access Journals (Sweden)

    Ning Cui

    2012-06-01

    Full Text Available Choosing novel materials and structures is important for enhancing the on-state current in tunnel field-effect transistors (TFETs. In this paper, we reveal that the on-state performance of TFETs is mainly determined by the energy band profile of the channel. According to this interpretation, we present a new concept of energy band profile modulation (BPM achieved with gate structure engineering. It is believed that this approach can be used to suppress the ambipolar effect. Based on this method, a Si TFET device with a symmetrical tri-material-gate (TMG structure is proposed. Two-dimensional numerical simulations demonstrated that the special band profile in this device can boost on-state performance, and it also suppresses the off-state current induced by the ambipolar effect. These unique advantages are maintained over a wide range of gate lengths and supply voltages. The BPM concept can serve as a guideline for improving the performance of nanoscale TFET devices.

  9. Electronic structure investigation of MoS2 and MoSe2 using angle-resolved photoemission spectroscopy and ab initio band structure studies.

    Science.gov (United States)

    Mahatha, S K; Patel, K D; Menon, Krishnakumar S R

    2012-11-28

    Angle-resolved photoemission spectroscopy (ARPES) and ab initio band structure calculations have been used to study the detailed valence band structure of molybdenite, MoS(2) and MoSe(2). The experimental band structure obtained from ARPES has been found to be in good agreement with the theoretical calculations performed using the linear augmented plane wave (LAPW) method. In going from MoS(2) to MoSe(2), the dispersion of the valence bands decreases along both k(parallel) and k(perpendicular), revealing the increased two-dimensional character which is attributed to the increasing interlayer distance or c/a ratio in these compounds. The width of the valence band and the band gap are also found to decrease, whereas the valence band maxima shift towards the higher binding energy from MoS(2) to MoSe(2).

  10. 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).

  11. Normal-metal quasiparticle traps for superconducting qubits

    Energy Technology Data Exchange (ETDEWEB)

    Hosseinkhani, Amin [Peter Grunberg Institute (PGI-2), Forschungszentrum Julich, D-52425 Julich (Germany); JARA-Institute for Quantum Information, RWTH Aachen University, D-52056 Aachen (Germany)

    2016-07-01

    Superconducting qubits are promising candidates to implement quantum computation, and have been a subject of intensive research in the past decade. Excitations of a superconductor, known as quasiparticles, can reduce the qubit performance by causing relaxation; the relaxation rate is proportional to the density of quasiparticles tunneling through Josephson junction. Here, we consider engineering quasiparticle traps by covering parts of a superconducting device with normal-metal islands. We utilize a phenomenological quasiparticle diffusion model to study both the decay rate of excess quasiparticles and the steady-state profile of the quasiparticle density in the device. We apply the model to various realistic configurations to explore the role of geometry and location of the traps.

  12. Relativistic band-structure calculations for CeTIn sub 5 (T=Ir and Co) and analysis of the energy bands by using tight-binding method

    CERN Document Server

    Maehira, T; Ueda, K; Hasegawa, A

    2003-01-01

    In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn sub 5 (T=Ir and Co), we employ the relativistic linear augmented-plane-wave (RLAPW) method to clarify the energy band structures and Fermi surfaces of those materials. The obtained energy bands mainly due to the large hybridization between Ce 4 f and In 5 p states well reproduce the Fermi surfaces consistent with the de Haas-van Alphen experimental results. However, when we attempt to understand magnetism and superconductively in CeTIn sub 5 from the microscopic viewpoint, the energy bands obtained in the RLAPW method are too complicated to analyze the system by further including electron correlations. Thus, it is necessary to prepare a more simplified model, keeping correctly the essential characters of the energy bands obtained in the band-structure calculation. For the purpose, we construct a tight-binding model for CeTIn sub 5 by including f-f and p-p hoppings as well as f-p hybridization, which are ex...

  13. Complex layered materials and periodic electromagnetic band-gap structures: Concepts, characterizations, and applications

    Science.gov (United States)

    Mosallaei, Hossein

    The main objective of this dissertation is to characterize and create insight into the electromagnetic performances of two classes of composite structures, namely, complex multi-layered media and periodic Electromagnetic Band-Gap (EBG) structures. The advanced and diversified computational techniques are applied to obtain their unique propagation characteristics and integrate the results into some novel applications. In the first part of this dissertation, the vector wave solution of Maxwell's equations is integrated with the Genetic Algorithm (GA) optimization method to provide a powerful technique for characterizing multi-layered materials, and obtaining their optimal designs. The developed method is successfully applied to determine the optimal composite coatings for Radar Cross Section (RCS) reduction of canonical structures. Both monostatic and bistatic scatterings are explored. A GA with hybrid planar/curved surface implementation is also introduced to efficiently obtain the optimal absorbing materials for curved structures. Furthermore, design optimization of the non-uniform Luneburg and 2-shell spherical lens antennas utilizing modal solution/GA-adaptive-cost function is presented. The lens antennas are effectively optimized for both high gain and suppressed grating lobes. The second part demonstrates the development of an advanced computational engine, which accurately computes the broadband characteristics of challenging periodic electromagnetic band-gap structures. This method utilizes the Finite Difference Time Domain (FDTD) technique with Periodic Boundary Condition/Perfectly Matched Layer (PBC/PML), which is efficiently integrated with the Prony scheme. The computational technique is successfully applied to characterize and present the unique propagation performances of different classes of periodic structures such as Frequency Selective Surfaces (FSS), Photonic Band-Gap (PBG) materials, and Left-Handed (LH) composite media. The results are

  14. Band structure and thermoelectric properties of half-Heusler semiconductors from many-body perturbation theory

    Science.gov (United States)

    Zahedifar, Maedeh; Kratzer, Peter

    2018-01-01

    Various ab initio approaches to the band structure of A NiSn and A CoSb half-Heusler compounds (A = Ti, Zr, Hf) are compared and their consequences for the prediction of thermoelectric properties are explored. Density functional theory with the generalized-gradient approximation (GGA), as well as the hybrid density functional HSE06 and ab initio many-body perturbation theory in the form of the G W0 approach, are employed. The G W0 calculations confirm the trend of a smaller band gap (0.75 to 1.05 eV) in A NiSn compared to the A CoSb compounds (1.13 to 1.44 eV) already expected from the GGA calculations. While in A NiSn materials the G W0 band gap is 20% to 50% larger than in HSE06, the fundamental gap of A CoSb materials is smaller in G W0 compared to HSE06. This is because G W0 , similar to PBE, locates the valence band maximum at the L point of the Brillouin zone, whereas it is at the Γ point in the HSE06 calculations. The differences are attributed to the observation that the relative positions of the d levels of the transition metal atoms vary among the different methods. Using the calculated band structures and scattering rates taking into account the band effective masses at the extrema, the Seebeck coefficients, thermoelectric power factors, and figures of merit Z T are predicted for all six half-Heusler compounds. Comparable performance is predicted for the n -type A NiSn materials, whereas clear differences are found for the p -type A CoSb materials. Using the most reliable G W0 electronic structure, ZrCoSb is predicted to be the most efficient material with a power factor of up to 0.07 W/(K2 m) at a temperature of 600 K. We find strong variations among the different ab initio methods not only in the prediction of the maximum power factor and Z T value of a given material, but also in comparing different materials to each other, in particular in the p -type thermoelectric materials. Thus we conclude that the most elaborate, but also most costly G W0

  15. Weakly nonlinear dispersion and stop-band effects for periodic structures

    DEFF Research Database (Denmark)

    Sorokin, Vladislav; Thomsen, Jon Juel

    of frequency band-gaps, i.e. frequency ranges in which elastic waves cannot propagate. Most existing analytical methods in the field are based on Floquet theory [1]; e.g. this holds for the classical Hill’s method of infinite determinants [1,2], and themethod of space-harmonics [3]. However, application...... of these methods for studying nonlinear problems isimpossible or cumbersome, since Floquet theory is applicable only for linear systems. Thus the nonlinear effects for periodic structures are not yet fully uncovered, while at the same time applications may demand effects of nonlinearity on structural response...... to be accounted for.The paper deals with analytically predicting dynamic response for nonlinear elastic structures with a continuous periodic variation in structural properties. Specifically, for a Bernoulli-Euler beam with aspatially continuous modulation of structural properties in the axial direction...

  16. A wave-bending structure at Ka-band using 3D-printed metamaterial

    Science.gov (United States)

    Wu, Junqiang; Liang, Min; Xin, Hao

    2018-03-01

    Three-dimensional printing technologies enable metamaterials of complex structures with arbitrary inhomogeneity. In this work, a 90° wave-bending structure at the Ka-band (26.5-40 GHz) based on 3D-printed metamaterials is designed, fabricated, and measured. The wave-bending effect is realized through a spatial distribution of varied effective dielectric constants. Based on the effective medium theory, different effective dielectric constants are accomplished by special, 3D-printable unit cells, which allow different ratios of dielectric to air at the unit cell level. In contrast to traditional, metallic-structure-included metamaterial designs, the reported wave-bending structure here is all dielectric and implemented by the polymer-jetting technique, which features rapid, low-cost, and convenient prototyping. Both simulation and experiment results demonstrate the effectiveness of the wave-bending structure.

  17. Band structure calculation of GaSe-based nanostructures using empirical pseudopotential method

    International Nuclear Information System (INIS)

    Osadchy, A V; Obraztsova, E D; Volotovskiy, S G; Golovashkin, D L; Savin, V V

    2016-01-01

    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. (paper)

  18. Helical quantum states in HgTe quantum dots with inverted band structures.

    Science.gov (United States)

    Chang, Kai; Lou, Wen-Kai

    2011-05-20

    We investigate theoretically the electron states in HgTe quantum dots (QDs) with inverted band structures. In sharp contrast to conventional semiconductor quantum dots, the quantum states in the gap of the HgTe QD are fully spin-polarized and show ringlike density distributions near the boundary of the QD and spin-angular momentum locking. The persistent charge currents and magnetic moments, i.e., the Aharonov-Bohm effect, can be observed in such a QD structure. This feature offers us a practical way to detect these exotic ringlike edge states by using the SQUID technique.

  19. Structure design for a 500 GeV S-band linear collider

    International Nuclear Information System (INIS)

    Hahne, P.; Holtkamp, N.; Klatt, R.; Weiland, T.

    1991-01-01

    Constant gradient structures with an accelerating gradient of 20 MeV per meter are commonly used with S-band frequency. The well known features of these travelling wave tubes provide a dedicated design for their use in the next generation linear collider. Some of the required design parameters for this tubes are presented within the whole concept of this collider with an active length of about 30 km. The choice of these parameters is explained and calculations concerning the structure are presented

  20. Babinet's principle and the band structure of surface waves on patterned metal arrays

    Science.gov (United States)

    Edmunds, J. D.; Taylor, M. C.; Hibbins, A. P.; Sambles, J. R.; Youngs, I. J.

    2010-05-01

    The microwave response of an array of square metal patches and its complementary structure, an array of square holes, has been experimentally studied. The resonant phenomena, which yield either enhanced transmission or reflection, are attributed to the excitation of diffractively coupled surface waves. The band structure of these surface modes has been quantified for both p-(transverse magnetic) and s-(transverse electric) polarized radiation and is found to be dependent on the periodicity of the electric and magnetic fields on resonance. The results are in excellent accord with predictions from finite element method modeling and the electromagnetic form of Babinet's principle [Babinet, C. R. Acad. Sci. 4, 638 (1837)].

  1. Babinet's principle and the band structure of surface waves on patterned metal arrays

    International Nuclear Information System (INIS)

    Edmunds, J. D.; Taylor, M. C.; Hibbins, A. P.; Sambles, J. R.; Youngs, I. J.

    2010-01-01

    The microwave response of an array of square metal patches and its complementary structure, an array of square holes, has been experimentally studied. The resonant phenomena, which yield either enhanced transmission or reflection, are attributed to the excitation of diffractively coupled surface waves. The band structure of these surface modes has been quantified for both p-(transverse magnetic) and s-(transverse electric) polarized radiation and is found to be dependent on the periodicity of the electric and magnetic fields on resonance. The results are in excellent accord with predictions from finite element method modeling and the electromagnetic form of Babinet's principle [Babinet, C. R. Acad. Sci. 4, 638 (1837)].

  2. Ab initio electronic band structure calculation of InP in the wurtzite phase

    Science.gov (United States)

    Dacal, Luis C. O.; Cantarero, Andrés

    2011-05-01

    We present ab initio calculations of the InP band structure in the wurtzite phase and compare it with that of the zincblende phase. In both calculations, we use the full potential linearized augmented plane wave method as implemented in the WIEN2k code and the modified Becke-Johnson exchange potential, which provides an improved value of the bandgap. The structural optimization of the wurtizte InP gives a=0.4150 nm, c=0.6912 nm, and an internal parameter u=0.371, showing the existence of a spontaneous polarization along the growth axis. As compared to the ideal wurtzite structure (that with the lattice parameter derived from the zincblende structure calculations), the actual wurtzite structure is compressed (-1.3%) in plane and expanded (0.7%) along the c-direction. The value of the calculated band gaps agrees well with recent optical experiments. The calculations are also consistent with the optical transitions found using polarized light.

  3. Adsorbate-induced modification of electronic band structure of epitaxial Bi(111) films

    Energy Technology Data Exchange (ETDEWEB)

    Matetskiy, A.V., E-mail: mateckij@iacp.dvo.ru [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); Bondarenko, L.V.; Tupchaya, A.Y.; Gruznev, D.V. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); Eremeev, S.V. [Institute of Strength Physics and Materials Science, 634021 Tomsk (Russian Federation); Tomsk State University, 634050 Tomsk (Russian Federation); Zotov, A.V. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation); Department of Electronics, Vladivostok State University of Economics and Service, 690600 Vladivostok (Russian Federation); Saranin, A.A. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation)

    2017-06-01

    Highlights: • Modification of electronic properties of ultrathin Bi films by adsorbates is demonstrated. • Due to electron doping from Cs adatoms, surface-state bands shift to higher binding energies. • As a result, only electron pockets are left in the Fermi map. • Tin acts as an acceptor dopant for Bi, shifting Fermi level upward. • As a result, only hole pockets are left in the Fermi map. - Abstract: Changes of the electronic band structure of Bi(111) films on Si(111) induced by Cs and Sn adsorption have been studied using angle-resolved photoemission spectroscopy and density functional theory calculations. It has been found that small amounts of Cs when it presents at the surface in a form of the adatom gas leads to shifting of the surface and quantum well states to the higher binding energies due to the electron donation from adsorbate to the Bi film. In contrast, adsorbed Sn dissolves into the Bi film bulk upon heating and acts as an acceptor dopant, that results in shifting of the surface and quantum well states upward to the lower binding energies. These results pave the way to manipulate with the Bi thin film electron band structure allowing to achieve a certain type of conductivity (electron or hole) with a single spin channel at the Fermi level making the adsorbate-modified Bi a reliable base for prospective spintronics applications.

  4. Structure of collective bands and deformations in {sup 74,76}Kr

    Energy Technology Data Exchange (ETDEWEB)

    Tripathy, K.C. [Physics Department, F M College, Balasore, 756 001 (India); Sahu, R. [Physics Department, Berhampur University, Berhampur, 760 007 (India)

    2000-08-01

    The structure of collective bands in {sup 74,76}Kr is studied within the framework of the deformed configuration mixing shell model based on Hartree-Fock states. The active single-particle orbits are 1p{sub 3/2}, 0f{sub 5/2}, 1p{sub 1/2} and 0g{sub 9/2} with {sup 56}Ni as the inert core. A modified Kuo interaction has been used for the above configuration space. The {sup 74}Kr nucleus is found to be the most deformed nucleus among the krypton isotopes which is in agreement with experiment. The deformation is found to decrease for the {sup 76}Kr isotope. The calculated positive- and negative-parity bandsagree quite well with the experiment for both the nuclei. A number of excited bands is also predicted. We have also calculated B(E2) values and compared them with available experimental data. The structure of the strongly coupled band built on K = 4{sup (+)} in {sup 76}Kr is also studied. (author)

  5. Reply to ``Comment on `Band structure engineering of graphene by strain: First-principles calculations' ''

    Science.gov (United States)

    Gui, Gui; Li, Jin; Zhong, Jianxin

    2009-10-01

    We reply to the Comment by Farjam and Rafii-Tabar [Phys. Rev. B 80, 167401 (2009)] on our paper [Phys. Rev. B 78, 075435 (2008)]. We show that the gap opening found in our paper is due to the use of a small number of k points in the calculation which prevents revealing the sharp contact of the two bands near K or R . Once a large number of k points is used, the density-functional theory (DFT) VASP codes give the same conclusion as obtained by Farjam and Rafii-Tabar by using the QUANTUM-ESPRESSO codes, namely, there is no gap opening in the band structure of graphene under small planar strain. We also point out that all other results in our paper remain correct, except for the conclusion of the gap opening. The results demonstrate the importance of using a large number of k points for determining the gap width of the band structure of graphene under strain as well as the validity of the DFT VASP codes for the system.

  6. Evolution of optical properties and band structure from amorphous to crystalline Ga2O3 films

    Directory of Open Access Journals (Sweden)

    Fabi Zhang

    2018-04-01

    Full Text Available The optical properties and band structure evolution from amorphous to crystalline Ga2O3 films was investigated in this work. Amorphous and crystalline Ga2O3 films were obtained by changing the growth substrate temperatures of pulsed laser deposition and the crystallinity increase with the rising of substrate temperature. The bandgap value and ultraviolet emission intensity of the films increase with the rising of crystallinity as observed by means of spectrophotometer and cathodoluminescence spectroscopy. Abrupt bandgap value and CL emission variations were observed when amorphous to crystalline transition took place. X-ray photoelectron spectroscopy core level spectra reveal that more oxygen vacancies and disorders exist in amorphous Ga2O3 film grown at lower substrate temperature. The valence band spectra of hard X-ray photoelectron spectroscopy present the main contribution from Ga 4sp for crystalline film deposited at substrate temperature of 500 oC, while extra subgap states has been observed in amorphous film deposited at 300 oC. The oxygen vacancy and the extra subgap density of states are suggested to be the parts of origin of bandgap and CL spectra variations. The experimental data above yields a realistic picture of optical properties and band structure variation for the amorphous to crystalline transition of Ga2O3 films.

  7. Evolution of optical properties and band structure from amorphous to crystalline Ga2O3 films

    Science.gov (United States)

    Zhang, Fabi; Li, Haiou; Cui, Yi-Tao; Li, Guo-Ling; Guo, Qixin

    2018-04-01

    The optical properties and band structure evolution from amorphous to crystalline Ga2O3 films was investigated in this work. Amorphous and crystalline Ga2O3 films were obtained by changing the growth substrate temperatures of pulsed laser deposition and the crystallinity increase with the rising of substrate temperature. The bandgap value and ultraviolet emission intensity of the films increase with the rising of crystallinity as observed by means of spectrophotometer and cathodoluminescence spectroscopy. Abrupt bandgap value and CL emission variations were observed when amorphous to crystalline transition took place. X-ray photoelectron spectroscopy core level spectra reveal that more oxygen vacancies and disorders exist in amorphous Ga2O3 film grown at lower substrate temperature. The valence band spectra of hard X-ray photoelectron spectroscopy present the main contribution from Ga 4sp for crystalline film deposited at substrate temperature of 500 oC, while extra subgap states has been observed in amorphous film deposited at 300 oC. The oxygen vacancy and the extra subgap density of states are suggested to be the parts of origin of bandgap and CL spectra variations. The experimental data above yields a realistic picture of optical properties and band structure variation for the amorphous to crystalline transition of Ga2O3 films.

  8. Largely Tunable Band Structures of Few-Layer InSe by Uniaxial Strain.

    Science.gov (United States)

    Song, Chaoyu; Fan, Fengren; Xuan, Ningning; Huang, Shenyang; Zhang, Guowei; Wang, Chong; Sun, Zhengzong; Wu, Hua; Yan, Hugen

    2018-01-31

    Because of the strong quantum confinement effect, few-layer γ-InSe exhibits a layer-dependent band gap, spanning the visible and near infrared regions, and thus recently has been drawing tremendous attention. As a two-dimensional material, the mechanical flexibility provides an additional tuning knob for the electronic structures. Here, for the first time, we engineer the band structures of few-layer and bulk-like InSe by uniaxial tensile strain and observe a salient shift of photoluminescence peaks. The shift rate of the optical gap is approximately 90-100 meV per 1% strain for four- to eight-layer samples, which is much larger than that for the widely studied MoS 2 monolayer. Density functional theory calculations well reproduce the observed layer-dependent band gaps and the strain effect and reveal that the shift rate decreases with the increasing layer number for few-layer InSe. Our study demonstrates that InSe is a very versatile two-dimensional electronic and optoelectronic material, which is suitable for tunable light emitters, photodetectors, and other optoelectronic devices.

  9. Study on frugmentation of one-quasiparticle and one-phonon states in the quasiparticle-phonon nuclear model

    International Nuclear Information System (INIS)

    Solov'ev, V.G.

    1980-01-01

    The general assumptions of the quasiparticle-phonon nuclear model are given. This model describes the few-quasiparticle components of the wave functions at low, intermediate and high excitation energies. The method of strength functions which plays a key role in describing complex nuclei is also presented. A further development of the quasiparticle-phonon nuclear model is outlined. The fragmentation of one-quasiparticle and one-phonon states over nuclear levels is studied. The results on the fragmentation of deep hole states in spherical nuclei are presented, which describe well the experimental data. The neutron strength functions and their spin dependence are calculated. A good agreement with experiment is obtained. The energies and widths of the giant resonances are calculated in spherical and deformed nuclei. The information on the many-quasiparticle components of excited state wave functions is shown to be very scarce. The necessity of studying the few-quasiparticle configurations is pointed out

  10. Density Functional Theory Calculations Revealing Metal-like Band Structures for Ultrathin Ge {111} and {211} Surface Layers.

    Science.gov (United States)

    Tan, Chih-Shan; Huang, Michael Hsuan-Yi

    2018-05-21

    To find out if germanium should also possess facet-dependent electrical conductivity properties, surface state density functional theory (DFT) calculations were performed on 1-6 layers of Ge (100), (110), (111), and (211) planes. Tunable Ge (100) and (110) planes always present the same semiconducting band structure with a band gap of 0.67 eV expected of bulk germanium. In contrast, 1, 2, 4, and 5 layers of Ge (111) and (211) plane models show metal-like band structures with continuous density of states (DOS) throughout the entire band. For 3 and 6 layers of Ge (111) and (211) plane models, the normal semiconducting band structure was obtained. The plane layers with metal-like band structures also show Ge-Ge bond length deviations and bond distortions, as well as significantly different 4s and 4p frontier orbital electron count and their relative percentages integrated over the valence and conduction bands from those of the semiconducting state. These differences should contribute to strikingly dissimilar band structures. The calculation results suggest observation of facet-dependent electrical conductivity properties of germanium materials, and transistors made of germanium may also need to consider the facet effects with shrinking dimensions approaching 3 nm. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. High power breakdown testing of a photonic band-gap accelerator structure with elliptical rods

    Directory of Open Access Journals (Sweden)

    Brian J. Munroe

    2013-01-01

    Full Text Available An improved single-cell photonic band-gap (PBG structure with an inner row of elliptical rods (PBG-E was tested with high power at a 60 Hz repetition rate at X-band (11.424 GHz, achieving a gradient of 128  MV/m at a breakdown probability of 3.6×10^{-3} per pulse per meter at a pulse length of 150 ns. The tested standing-wave structure was a single high-gradient cell with an inner row of elliptical rods and an outer row of round rods; the elliptical rods reduce the peak surface magnetic field by 20% and reduce the temperature rise of the rods during the pulse by several tens of degrees, while maintaining good damping and suppression of high order modes. When compared with a single-cell standing-wave undamped disk-loaded waveguide structure with the same iris geometry under test at the same conditions, the PBG-E structure yielded the same breakdown rate within measurement error. The PBG-E structure showed a greatly reduced breakdown rate compared with earlier tests of a PBG structure with round rods, presumably due to the reduced magnetic fields at the elliptical rods vs the fields at the round rods, as well as use of an improved testing methodology. A post-testing autopsy of the PBG-E structure showed some damage on the surfaces exposed to the highest surface magnetic and electric fields. Despite these changes in surface appearance, no significant change in the breakdown rate was observed in testing. These results demonstrate that PBG structures, when designed with reduced surface magnetic fields and operated to avoid extremely high pulsed heating, can operate at breakdown probabilities comparable to undamped disk-loaded waveguide structures and are thus viable for high-gradient accelerator applications.

  12. Three-dimensional ordered particulate structures: Method to retrieve characteristics from photonic band gap data

    International Nuclear Information System (INIS)

    Miskevich, Alexander A.; Loiko, Valery A.

    2015-01-01

    A method to retrieve characteristics of ordered particulate structures, such as photonic crystals, is proposed. It is based on the solution of the inverse problem using data on the photonic band gap (PBG). The quasicrystalline approximation (QCA) of the theory of multiple scattering of waves and the transfer matrix method (TMM) are used. Retrieval of the refractive index of particles is demonstrated. Refractive indices of the artificial opal particles are estimated using the published experimental data. - Highlights: • A method to retrieve characteristics of photonic crystals is proposed. • The method is based on the inverse problem solution using the photonic band gap data. • Retrieval of the refractive index of photonic crystal particles is demonstrated. • Retrieval results show inhomogeneous distribution of synthetic opal particle pores

  13. Development of small C-band standing-wave accelerator structure

    International Nuclear Information System (INIS)

    Miura, S.; Takahashi, A.; Hisanaga, N.; Sekido, H.; Yoshizumi, A.

    2000-01-01

    We have newly developed a compact C-band (5712 MHz) standing-wave accelerator for the medical product/waste sterilization applications. The accelerator consists of an electron gun operating at 25 kV DC followed by a single-cell pre-buncher and 3-cell buncher section, and 11-cell of the side-coupled standing-wave accelerating structure. The total length including the electron gun is about 600 mm. The first high-power test was performed in March 2000, where the accelerator successively generated the electron beam of 9 MeV energy and 160 mA peak-current at 3.8 MW RF input power. Mitsubishi Heavy Industry starts to serve the sterilization systems using C-band accelerator reported here, and also supplies the accelerator components for the medical oncology applications. (author)

  14. 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.

  15. 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

    2016-09-09

    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.

  16. Enhanced modeling of band nonparabolicity with application to a mid-IR quantum cascade laser structure

    International Nuclear Information System (INIS)

    Vukovic, N; Radovanovic, J; Milanovic, V

    2014-01-01

    We analyze the influence of conduction-band nonparabolicity on bound electronic states in the active region of a quantum cascade laser (QCL). Our model assumes expansion of the conduction-band dispersion relation up to a fourth order in wavevector and use of a suitable second boundary condition at the interface of two III-V semiconductor layers. Numerical results, obtained by the transfer matrix method, are presented for two mid-infrared GaAs/Al 0.33 Ga 0.67 As QCL active regions, and they are in very good agreement with experimental data found in the literature. Comparison with a different nonparabolicity model is presented for the example of a GaAs/Al 0.38 Ga 0.62 As-based mid-IR QCL. Calculations have also been carried out for one THz QCL structure to illustrate the possible application of the model in the terahertz part of the spectrum. (paper)

  17. 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.

  18. Conduction band structure and electron mobility in uniaxially strained Si via externally applied strain in nanomembranes

    Energy Technology Data Exchange (ETDEWEB)

    Chen Feng [Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Euaruksakul, Chanan; Himpsel, F J; Lagally, Max G [University of Wisconsin-Madison, Madison, WI 53706 (United States); Liu Zheng; Liu Feng, E-mail: lagally@engr.wisc.edu [University of Utah, Salt Lake City, UT 84112 (United States)

    2011-08-17

    Strain changes the band structure of semiconductors. We use x-ray absorption spectroscopy to study the change in the density of conduction band (CB) states when silicon is uniaxially strained along the [1 0 0] and [1 1 0] directions. High stress can be applied to silicon nanomembranes, because their thinness allows high levels of strain without fracture. Strain-induced changes in both the sixfold degenerate {Delta} valleys and the eightfold degenerate L valleys are determined quantitatively. The uniaxial deformation potentials of both {Delta} and L valleys are directly extracted using a strain tensor appropriate to the boundary conditions, i.e., confinement in the plane in the direction orthogonal to the straining direction, which correspond to those of strained CMOS in commercial applications. The experimentally determined deformation potentials match the theoretical predictions well. We predict electron mobility enhancement created by strain-induced CB modifications.

  19. Band structure of comb-like photonic crystals containing meta-materials

    Science.gov (United States)

    Weng, Yi; Wang, Zhi-Guo; Chen, Hong

    2007-09-01

    We study the transmission properties and band structure of comb-like photonic crystals (PC) with backbones constructed of meta-materials (negative-index materials) within the frame of the interface response theory. The result shows the existence of a special band gap at low frequency. This gap differs from the Bragg gaps in that it is insensitive to the geometrical scaling and disorder. In comparison with the zero-average-index gap in one-dimensional PC made of alternating positive- and negative-index materials, the gap is obviously deeper and broader, given the same system parameters. In addition, the behavior of its gap-edges is also different. One gap-edge is decided by the average permittivity whereas the other is only subject to the changing of the permeability of the backbone. Due to this asymmetry of the two gap-edges, the broadening of the gap could be realized with much freedom and facility.

  20. Synthesis, band structure, and optical properties of Ba2ZnV2O8

    International Nuclear Information System (INIS)

    Chen, D.-G.; Cheng, W.-D.; Wu, D.-S.; Zhang, H.; Zhang, Y.-C.; Gong, Y.-J.; Kan, Z.-G.

    2004-01-01

    A novel compound Ba 2 ZnV 2 O 8 has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2 1 /c with a=7.9050(16), b=16.149(3), c=6.1580(12)A, β=90.49(3). It builds up from 1-D branchy chains of [ZnV 2 O 8 4- ] ∞ , and the Ba 2+ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba 2 ZnV 2 O 8 is an insulator with direct band gap of 3.48eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V-O bonds are mostly covalence characters and Zn-O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba-O than between the Zn-O. The refractive index of n x , n y , and n z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060nm for Ba 2 ZnV 2 O 8 crystal

  1. Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Othman, Mohamed A. K.; Veysi, Mehdi; Capolino, Filippo [Department of Electrical Engineering and Computer Science, University of California, Irvine, California 92697 (United States); Figotin, Alexander [Department of Mathematics, University of California, Irvine, California 92697 (United States)

    2016-03-15

    We propose a new amplification regime based on a synchronous operation of four degenerate electromagnetic (EM) modes in a slow-wave structure and the electron beam, referred to as super synchronization. These four EM modes arise in a Fabry-Pérot cavity when degenerate band edge (DBE) condition is satisfied. The modes interact constructively with the electron beam resulting in superior amplification. In particular, much larger gains are achieved for smaller beam currents compared to conventional structures based on synchronization with only a single EM mode. We demonstrate giant gain scaling with respect to the length of the slow-wave structure compared to conventional Pierce type single mode traveling wave tube amplifiers. We construct a coupled transmission line model for a loaded waveguide slow-wave structure exhibiting a DBE, and investigate the phenomenon of giant gain via super synchronization using the Pierce model generalized to multimode interaction.

  2. Development of Electromagnetic Band Gap Structures in the Perspective of Microstrip Antenna Design

    Directory of Open Access Journals (Sweden)

    Md. Shahidul Alam

    2013-01-01

    Full Text Available Electromagnetic band gap (EBG technology has become a significant breakthrough in the radio frequency (RF and microwave applications due to their unique band gap characteristics at certain frequency ranges. Since 1999, the EBG structures have been investigated for improving performances of numerous RF and microwave devices utilizing the surface wave suppression and the artificial magnetic conductor (AMC properties of these special type metamaterial. Issues such as compactness, wide bandwidth with low attenuation level, tunability, and suitability with planar circuitry all play an important role in the design of EBG structures. Remarkable efforts have been undertaken for the development of EBG structures to be compatible with a wide range of wireless communication systems. This paper provides a comprehensive review on various EBG structures such as three-, two-, and one-dimensional (3D, 2D, and 1D EBG, mushroom and uniplanar EBG, and their successive advancement. Considering the related fabrication complexities, implementation of vialess EBG is an attractive topic for microwave engineers. For microstrip antennas, EBG structures are used in diversified ways, which of course found to be effective except in some cases. The EBG structures are also successfully utilized in antenna arrays for reducing the mutual coupling between elements of the array. Current challenges and limitations of the typical microstrip antennas and different EBG structures are discussed in details with some possible suggestions. Hopefully, this survey will guide to increasing efforts towards the development of more compact, wideband, and high-efficient uniplanar EBG structures for performance enhancement of antenna and other microwave devices.

  3. Spin splitting in band structures of BiTeX (X=Cl, Br, I) monolayers

    Science.gov (United States)

    Hvazdouski, D. C.; Baranava, M. S.; Stempitsky, V. R.

    2018-04-01

    In systems with breaking of inversion symmetry a perpendicular electric field arises that interacts with the conduction electrons. It may give rise to electron state splitting even without influence of external magnetic field due to the spin-orbital interaction (SOI). Such a removal of the spin degeneracy is called the Rashba effect. Nanostructure with the Rashba effect can be part of a spin transistor. Spin degeneracy can be realized in a channel from a material of this type without additive of magnetic ions. Lack of additive increases the charge carrier mobility and reliability of the device. Ab initio simulations of BiTeX (X=Cl, Br, I) monolayers have been carried out using VASP wherein implemented DFT method. The study of this structures is of interest because such sort of structures can be used their as spin-orbitronics materials. The crystal parameters of BiTeCl, BiTeBr, BiTeI have been determined by the ionic relaxation and static calculations. It is necessary to note that splitting of energy bands occurs in case of SOI included. The values of the Rashba coefficient aR (in the range from 6.25 to 10.00 eV·Å) have high magnitudes for spintronics materials. Band structure of monolayers structures have ideal Rashba electron gas, i.e. there no other energy states near to Fermi level except Rashba states.

  4. 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.

  5. 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.

  6. Analysis of two- and four-quasiparticle states in lead isotopes

    International Nuclear Information System (INIS)

    Pomar, C.; Insolia, A.

    1990-01-01

    In the framework of a quasiparticle multistep shell model method we study four-quasiparticle states in lead isotopes. For this we first calculate single-quasiparticle quantities within the BCS formalism and two-quasiparticle states within a QRPA. Finally the four-quasiparticle basis set of states is formed as the tensorial product of two-quasiparticle states previously evaluated. The resulting spectra agree reasonable well with available experimental data. A number of as yet undetected states are predicted. (orig.)

  7. A quantitative study of quasiparticle traps using the single-Cooper-pair-transistor

    OpenAIRE

    Court, N. A.; Ferguson, A. J.; Lutchyn, Roman; Clark, R. G.

    2007-01-01

    We use radio-frequency reflectometry to measure quasiparticle tunneling rates in the single-Cooper-pair-transistor. Devices with and without quasiparticle traps in proximity to the island are studied. A $10^2$ to $10^3$-fold reduction in the quasiparticle tunneling rate onto the island is observed in the case of quasiparticle traps. In the quasiparticle trap samples we also measure a commensurate decrease in quasiparticle tunneling rate off the island.

  8. Effect of superconductivity on the cubic to tetragonal structural transition due to a two-fold degenerate electronic band

    International Nuclear Information System (INIS)

    Ghatak, S.K.; Khanra, B.C.; Ray, D.K.

    1978-01-01

    The effect of the BCS superconductivity on the cubic to tetragonal structural transition arising from a two-fold degenerate electronic band is investigated within the mean field approximation. The phase diagram of the two transitions is given for a half filled esub(g)-band. Modification of the two transitions when they are close together is also discussed. (author)

  9. High power experimental studies of hybrid photonic band gap accelerator structures

    Directory of Open Access Journals (Sweden)

    JieXi Zhang

    2016-08-01

    Full Text Available This paper reports the first high power tests of hybrid photonic band gap (PBG accelerator structures. Three hybrid PBG (HPBG structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM_{02} mode, with suppression of both lower order modes, such as the TM_{11} mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion of the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19  MV/m, corresponding to a surface electric field of 78  MV/m, with a breakdown probability of 5×10^{-1} per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20  MV/m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. This research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.

  10. Microscopic bosonization of band structures: x-ray processes beyond the Fermi edge

    Science.gov (United States)

    Snyman, Izak; Florens, Serge

    2017-11-01

    Bosonization provides a powerful analytical framework to deal with one-dimensional strongly interacting fermion systems, which makes it a cornerstone in quantum many-body theory. However, this success comes at the expense of using effective infrared parameters, and restricting the description to low energy states near the Fermi level. We propose a radical extension of the bosonization technique that overcomes both limitations, allowing computations with microscopic lattice Hamiltonians, from the Fermi level down to the bottom of the band. The formalism rests on the simple idea of representating the fermion kinetic term in the energy domain, after which it can be expressed in terms of free bosonic degrees of freedom. As a result, one- and two-body fermionic scattering processes generate anharmonic boson-boson interactions, even in the forward channel. We show that up to moderate interaction strengths, these non-linearities can be treated analytically at all energy scales, using the x-ray emission problem as a showcase. In the strong interaction regime, we employ a systematic variational solution of the bosonic theory, and obtain results that agree quantitatively with an exact diagonalization of the original one-particle fermionic model. This provides a proof of the fully microscopic character of bosonization, on all energy scales, for an arbitrary band structure. Besides recovering the known x-ray edge singularity at the emission threshold, we find strong signatures of correlations even at emission frequencies beyond the band bottom.

  11. Numerical calculation of acoustic radiation from band-vibrating structures via FEM/FAQP method

    Directory of Open Access Journals (Sweden)

    GAO Honglin

    2017-08-01

    Full Text Available The Finite Element Method (FEM combined with the Frequency Averaged Quadratic Pressure method (FAQP are used to calculate the acoustic radiation of structures excited in the frequency band. The surface particle velocity of stiffened cylindrical shells under frequency band excitation is calculated using finite element software, the normal vibration velocity is converted from the surface particle velocity to calculate the average energy source (frequency averaged across intensity, frequency averaged across pressure and frequency averaged across velocity, and the FAQP method is used to calculate the average sound pressure level within the bandwidth. The average sound pressure levels are then compared with the bandwidth using finite element and boundary element software, and the results show that FEM combined with FAQP is more suitable for high frequencies and can be used to calculate the average sound pressure level in the 1/3 octave band with good stability, presenting an alternative to applying frequency-by-frequency calculation and the average frequency process. The FEM/FAQP method can be used as a prediction method for calculating acoustic radiation while taking the randomness of vibration at medium and high frequencies into consideration.

  12. Electronic band structure of Two-Dimensional WS2/Graphene van der Waals Heterostructures

    Science.gov (United States)

    Henck, Hugo; Ben Aziza, Zeineb; Pierucci, Debora; Laourine, Feriel; Reale, Francesco; Palczynski, Pawel; Chaste, Julien; Silly, Mathieu G.; Bertran, François; Le Fèvre, Patrick; Lhuillier, Emmanuel; Wakamura, Taro; Mattevi, Cecilia; Rault, Julien E.; Calandra, Matteo; Ouerghi, Abdelkarim

    2018-04-01

    Combining single-layer two-dimensional semiconducting transition-metal dichalcogenides (TMDs) with a graphene layer in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these heterostructures. Here, we report the electronic and structural properties of transferred single-layer W S2 on epitaxial graphene using micro-Raman spectroscopy, angle-resolved photoemission spectroscopy measurements, and density functional theory (DFT) calculations. The results show good electronic properties as well as a well-defined band arising from the strong splitting of the single-layer W S2 valence band at the K points, with a maximum splitting of 0.44 eV. By comparing our DFT results with local and hybrid functionals, we find the top valence band of the experimental heterostructure is close to the calculations for suspended single-layer W S2 . Our results provide an important reference for future studies of electronic properties of W S2 and its applications in valleytronic devices.

  13. Novel semiconductor solar cell structures: The quantum dot intermediate band solar cell

    International Nuclear Information System (INIS)

    Marti, A.; Lopez, N.; Antolin, E.; Canovas, E.; Stanley, C.; Farmer, C.; Cuadra, L.; Luque, A.

    2006-01-01

    The Quantum Dot Intermediate Band Solar Cell (QD-IBSC) has been proposed for studying experimentally the operating principles of a generic class of photovoltaic devices, the intermediate band solar cells (IBSC). The performance of an IBSC is based on the properties of a semiconductor-like material which is characterised by the existence of an intermediate band (IB) located within what would otherwise be its conventional bandgap. The improvement in efficiency of the cell arises from its potential (i) to absorb below bandgap energy photons and thus produce additional photocurrent, and (ii) to inject this enhanced photocurrent without degrading its output photo-voltage. The implementation of the IBSC using quantum dots (QDs) takes advantage of the discrete nature of the carrier density of states in a 0-dimensional nano-structure, an essential property for realising the IB concept. In the QD-IBSC, the IB arises from the confined electron states in an array of quantum dots. This paper reviews the operation of the first prototype QD-IBSCs and discusses some of the lessons learnt from their characterisation

  14. Study of the structure of yrast bands of neutron-rich 114-124Pd isotopes

    Science.gov (United States)

    Chaudhary, Ritu; Devi, Rani; Khosa, S. K.

    2018-02-01

    The projected shell model calculations have been carried out in the neutron-rich 114-124Pd isotopic mass chain. The results have been obtained for the deformation systematics of E(2+1) and E(4+1)/E({2}+1) values, BCS subshell occupation numbers, yrast spectra, backbending phenomena, B( E2) transition probabilities and g-factors in these nuclei. The observed systematics of E(2+1) values and R_{42} ratios in the 114-124Pd isotopic mass chain indicate that there is a decrease of collectivity as the neutron number increases from 68 to 78. The occurrence of backbending in these nuclei as well as the changes in the calculated B( E2) transition probabilities and g -factors predict that there are changes in the structure of yrast bands in these nuclei. These changes occur at the spin where there is crossing of g-band by 2-qp bands. The predicted backbendings and predicted values of B( E2)s and g-factors in some of the isotopes need to be confirmed experimentally.

  15. Novel semiconductor solar cell structures: The quantum dot intermediate band solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Marti, A. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain)]. E-mail: amarti@etsit.upm.es; Lopez, N. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Antolin, E. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Canovas, E. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Stanley, C. [Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Farmer, C. [Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Cuadra, L. [Departamento de Teoria de la Senal y Comunicaciones- Escuela Politecnica Superior, Universidad de Alcala, Ctra. Madrid-Barcelona, km. 33600, 28805-Alcala de Henares (Madrid) (Spain); Luque, A. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain)

    2006-07-26

    The Quantum Dot Intermediate Band Solar Cell (QD-IBSC) has been proposed for studying experimentally the operating principles of a generic class of photovoltaic devices, the intermediate band solar cells (IBSC). The performance of an IBSC is based on the properties of a semiconductor-like material which is characterised by the existence of an intermediate band (IB) located within what would otherwise be its conventional bandgap. The improvement in efficiency of the cell arises from its potential (i) to absorb below bandgap energy photons and thus produce additional photocurrent, and (ii) to inject this enhanced photocurrent without degrading its output photo-voltage. The implementation of the IBSC using quantum dots (QDs) takes advantage of the discrete nature of the carrier density of states in a 0-dimensional nano-structure, an essential property for realising the IB concept. In the QD-IBSC, the IB arises from the confined electron states in an array of quantum dots. This paper reviews the operation of the first prototype QD-IBSCs and discusses some of the lessons learnt from their characterisation.

  16. Effective distributions of quasiparticles for thermal photons

    Science.gov (United States)

    Monnai, Akihiko

    2015-07-01

    It has been found in recent heavy-ion experiments that the second and the third flow harmonics of direct photons are larger than most theoretical predictions. In this study, I construct effective parton phase-space distributions with in-medium interaction using quasiparticle models so that they are consistent with a lattice QCD equation of state. Then I investigate their effects on thermal photons using a hydrodynamic model. Numerical results indicate that elliptic flow and transverse momentum spectra are modified by the corrections to Fermi-Dirac and Bose-Einstein distributions.

  17. Quasiparticles in QCD thermodynamics and applications

    International Nuclear Information System (INIS)

    Schneider, R.A.; Renk, T.

    2002-01-01

    We propose a novel quasiparticle interpretation of the equation of state of deconfined QCD at finite temperature. Using appropriate thermal masses, we introduce a phenomenological parametrization of the onset of confinement in the vicinity of the phase transition. Lattice results of the energy density, the pressure and the interaction measure of pure SU(3) gauge theory are well reproduced. A relation between the thermal energy density of the Yang-Mills vacuum and the chromomagnetic condensate left angle B 2 right angle T is found. We also present the two flavour QCD equation of state for realistic quark masses and apply the model to dilepton production in ultrarelativistic heavy-ion collisions. (orig.)

  18. Nonequilibrium Quasiparticle Distribution Induced by Kondo Defects

    Science.gov (United States)

    Kroha, J.; Zawadowski, A.

    2002-04-01

    It is shown that in resistive nanowires out of equilibrium containing either single- or two-channel Kondo impurities the distribution function f(E,U) obeys scaling behavior in terms of the quasiparticle energy E and the bias voltage U. The numerically calculated f(E,U) curves explain quantitatively recent experiments on Cu and Au nanowires. The systematics of the impurity concentration cimp extracted from the comparison between theory and results on various Cu and Au samples strongly suggests that in these systems the scaling arises from magnetic Kondo impurities.

  19. Wire measurement of impedance of an X-band accelerating structure

    CERN Document Server

    Baboi, N; Dolgashev, V A; Jones, R M; Lewandowski, J R; Tantawi, S G; Wang, J W

    2004-01-01

    Several tens of thousands of accelerator structures will be needed for the next generation of linear collders known as the GLC/NLC (Global Linear Collider/Next Linear Collider). To prevent the beam being driven into a disruptive BBU (Beam Break Up) mode or at the very least, the emittance being signifcantly diluted, it is important to damp down the wakefield left by driving bunches to a manageable level. Manufacturing errors and errors in design need to be measurable and compared with predictions. We develop a circuit model of wire-loaded X-band accelerator structures. This enables the wakefield (the inverse transform of the beam impedance) to be readily computed and compared with the wire measurement. We apply this circuit model to the latest series of accelerating for the GLC/NLC. This circuit model is based upon the single-cell model developed in [1] extended here to complete, multi-cell structures.

  20. Creation of quasi-Dirac points in the Floquet band structure of bilayer graphene.

    Science.gov (United States)

    Cheung, W M; Chan, K S

    2017-06-01

    We study the Floquet quasi-energy band structure of bilayer graphene when it is illuminated by two laser lights with frequencies [Formula: see text] and [Formula: see text] using Floquet theory. We focus on the dynamical gap formed by the conduction band with Floquet index  =  -1 and the valence band with Floquet index  =  +1 to understand how Dirac points can be formed. It is found that the dynamical gap does not have rotation symmetry in the momentum space, and quasi-Dirac points, where the conduction and valence bands almost touch, can be created when the dynamical gap closes along some directions with suitably chosen radiation parameters. We derive analytical expressions for the direction dependence of the dynamical gaps using Lowdin perturbation theory to gain a better understanding of the formation of quasi-Dirac points. When both radiations are circularly polarized, the gap can be exactly zero along some directions, when only the first and second order perturbations are considered. Higher order perturbations can open a very small gap in this case. When both radiations are linearly polarized, the gap can be exactly zero up to the fourth order perturbation and more than one quasi-Dirac point is formed. We also study the electron velocity around a dynamical gap and show that the magnitude of the velocity drops to values close to zero when the k vector is near to the gap minimum. The direction of the velocity also changes around the gap minimum, and when the gap is larger in value the change in the velocity direction is more gradual. The warping effect does not affect the formation of a Dirac point along the k x axis, while it prevents its formation when there is phase shift between the two radiations.

  1. 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

    2017-06-14

    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 NO 2 adsorption. Measurements of the temperature dependence of resistivity of single ultrathin Te nanowire field-effect transistor (FET) devices exposed to increasing amounts of NO 2 reveal a gradual transition from a semiconducting to a metallic state. Gradual quenching of vibrational Raman modes of Te with increasing concentration of NO 2 supports the appearance of a metallic state in NO 2 adsorbed Te. Ab initio simulations attribute these observations to the appearance of midgap states in NO 2 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.

  2. Effect of species structure and dielectric constant on C-band forest backscatter

    Science.gov (United States)

    Lang, R. H.; Landry, R.; Kilic, O.; Chauhan, N.; Khadr, N.; Leckie, D.

    1993-01-01

    A joint experiment between Canadian and USA research teams was conducted early in Oct. 1992 to determine the effect of species structure and dielectric variations on forest backscatter. Two stands, one red pine and one jack pine, in the Petawawa National Forestry Institute (PNFI) were utilized for the experiment. Extensive tree architecture measurements had been taken by the Canada Centre for Remote Sensing (CCRS) several months earlier by employing a Total Station surveying instrument which provides detailed information on branch structure. A second part of the experiment consisted of cutting down several trees and using dielectric probes to measure branch and needle permittivity values at both sites. The dielectric and the tree geometry data were used in the George Washington University (GWU) Vegetation Model to determine the C band backscattering coefficients of the individual stands for VV polarization. The model results show that backscatter at C band comes mainly from the needles and small branches and the upper portion of the trunks acts only as an attenuator. A discussion of variation of backscatter with specie structure and how dielectric variations in needles for both species may affect the total backscatter returns is provided.

  3. Band structures in a two-dimensional phononic crystal with rotational multiple scatterers

    Science.gov (United States)

    Song, Ailing; Wang, Xiaopeng; Chen, Tianning; Wan, Lele

    2017-03-01

    In this paper, the acoustic wave propagation in a two-dimensional phononic crystal composed of rotational multiple scatterers is investigated. The dispersion relationships, the transmission spectra and the acoustic modes are calculated by using finite element method. In contrast to the system composed of square tubes, there exist a low-frequency resonant bandgap and two wide Bragg bandgaps in the proposed structure, and the transmission spectra coincide with band structures. Specially, the first bandgap is based on locally resonant mechanism, and the simulation results agree well with the results of electrical circuit analogy. Additionally, increasing the rotation angle can remarkably influence the band structures due to the transfer of sound pressure between the internal and external cavities in low-order modes, and the redistribution of sound pressure in high-order modes. Wider bandgaps are obtained in arrays composed of finite unit cells with different rotation angles. The analysis results provide a good reference for tuning and obtaining wide bandgaps, and hence exploring the potential applications of the proposed phononic crystal in low-frequency noise insulation.

  4. Compton profiles and band structure calculations of CdS and CdTe

    International Nuclear Information System (INIS)

    Heda, N.L.; Mathur, S.; Ahuja, B.L.; Sharma, B.K.

    2007-01-01

    In this paper we present the isotropic Compton profiles of zinc-blende CdS and CdTe measured at an intermediate resolution of 0.39 a.u. using our 20 Ci 137 Cs Compton spectrometer. The electronic band structure calculations for both the zinc-blende structure compounds and also wurtzite CdS have been undertaken using various schemes of ab-initio linear combination of atomic orbitals calculations implemented in CRYSTAL03 code. The band structure and Mulliken's populations are reported using density functional scheme. In case of wurtzite CdS, our theoretical anisotropies in directional Compton profiles are compared with available experimental data. In case of both the zinc-blende compounds, the isotropic experimental profiles are found to be in better agreement with the present Hartree-Fock calculations. A study of the equal-valence-electron-density experimental profiles of zinc-blende CdS and CdTe shows that the CdS is more ionic than CdTe. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. 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

  6. Band structure and dielectric function of TlInTe2

    International Nuclear Information System (INIS)

    Wakita, K.; Shim, Y.; Orudzhev, G.; Mamedov, N.; Hashimzade, F.

    2006-01-01

    The band structure of ternary chain TlInTe 2 was calculated with allowance for non-locality of ionic pseudo-potentials. The dielectric function, as well as the effective masses of holes and electrons, the effective number of valence electrons, and the function of characteristic losses were determined. The results of comparison between the calculated dielectric function and the one obtained ellipsometrically in the spectral range from 0.85 to 6 eV are quite favorable. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  7. High gradient test of the C-band choke-mode type accelerating structure

    International Nuclear Information System (INIS)

    Inagaki, T.; Shintake, T.; Baba, H.; Togawa, K.; Onoe, K.; Marechal, X.; Takashima, T.; Takahashi, S.; Matsumoto, H.

    2004-01-01

    The C-band (5712 MHz) choke-mode type accelerating structure will be used for SPring-8 Compact SASE-FEL Source (SCSS). To make the accelerator length short, we designed the field gradient as high as 40 MV/m. Since it is higher gradient than other traditional electron accelerators, we have to carefully check its performance (RF breakdown, dark current emission, etc.) in the high gradient test stand. The first experiment will be scheduled in this summer. In this paper, we will describe the preparation progress for the test. (author)

  8. Calculation of the band structure of 2d conducting polymers using the network model

    International Nuclear Information System (INIS)

    Sabra, M. K.; Suman, H.

    2007-01-01

    the network model has been used to calculate the band structure the gap energy and Fermi level of conducting polymers in two dimensions. For this purpose, a geometrical classification of possible polymer chains configurations in two dimensions has been introduced leading to a classification of the unit cells based on the number of bonds in them. The model has been applied to graphite in 2D, represented by a three bonds unit cell, and, as a new case, the anti-parallel Polyacetylene chains (PA) in two dimensions, represented by a unit cell with four bons. The results are in good agreement with the first principles calculations. (author)

  9. 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.

  10. Lam\\'e polynomials, hyperelliptic reductions and Lam\\'e band structure

    OpenAIRE

    Maier, Robert S.

    2003-01-01

    The band structure of the Lam\\'e equation, viewed as a one-dimensional Schr\\"odinger equation with a periodic potential, is studied. At integer values of the degree parameter l, the dispersion relation is reduced to the l=1 dispersion relation, and a previously published l=2 dispersion relation is shown to be partially incorrect. The Hermite-Krichever Ansatz, which expresses Lam\\'e equation solutions in terms of l=1 solutions, is the chief tool. It is based on a projection from a genus-l hype...

  11. Intrinsic and experimental quasiparticle recombination times in superconducting films

    International Nuclear Information System (INIS)

    Eisenmenger, W.; Lassmann, K.; Trumpp, H.J.; Krauss, R.

    1977-01-01

    Experimental quasiparticle recombination lifetime data for superconducting Al, Sn, and Pb films are compared with calculations based on a ray acoustic model taking account of the film thickness dependence of the reabsorption of recombination phonons. Information on the true or intrinsic quasiparticle recombination lifetime obtained from these and other data is discussed. (orig.) [de

  12. Asymptotic kinetic theory of magnetized plasmas: quasi-particle concept

    International Nuclear Information System (INIS)

    Sosenko, P.P.; Zagorodny, A.H.

    2004-01-01

    The asymptotic kinetic theory of magnetized plasmas is elaborated within the context of general statistical approach and asymptotic methods, developed by M. Krylov and M. Bohol'ubov, for linear and non-linear dynamic systems with a rapidly rotating phase. The quasi-particles are introduced already on the microscopic level. Asymptotic expansions enable to close the description for slow processes, and to relate consistently particles and guiding centres to quasi-particles. The kinetic equation for quasi-particles is derived. It makes a basis for the reduced description of slow collective phenomena in the medium. The kinetic equation for quasi-particles takes into account self-consistent interaction fields, quasi-particle collisions and collective-fluctuation-induced relaxation of quasi-particle distribution function. The relationships between the distribution functions for particles, guiding centres and quasi-particles are derived taking into account fluctuations, which can be especially important in turbulent states. In this way macroscopic (statistical) particle properties can be obtained from those of quasi-particles in the general case of non-equilibrium. (authors)

  13. Measurement of filling factor 5/2 quasiparticle interference with observation of charge e/4 and e/2 period oscillations.

    Science.gov (United States)

    Willett, R L; Pfeiffer, L N; West, K W

    2009-06-02

    A standing problem in low-dimensional electron systems is the nature of the 5/2 fractional quantum Hall (FQH) state: Its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices may be used to manipulate and measure quantum Hall edge excitations. Here we use a small-area edge state interferometer designed to observe quasiparticle interference effects. Oscillations consistent in detail with the Aharonov-Bohm effect are observed for integer quantum Hall and FQH states (filling factors nu = 2, 5/3, and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these factors as charge calibrations, periodic transmission through the device consistent with quasiparticle charge e/4 is observed at nu = 5/2 and at lowest temperatures. The principal finding of this work is that, in addition to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at 5/2 nu and at lowest temperatures. Properties of the e/4 and e/2 oscillations are examined with the device sensitivity sufficient to observe temperature evolution of the 5/2 quasiparticle interference. In the model of quasiparticle interference, this presence of an effective e/2 period may empirically reflect an e/2 quasiparticle charge or may reflect multiple passes of the e/4 quasiparticle around the interferometer. These results are discussed within a picture of e/4 quasiparticle excitations potentially possessing non-Abelian statistics. These studies demonstrate the capacity to perform interferometry on 5/2 excitations and reveal properties important for understanding this state and its excitations.

  14. Effect of RF Parameters on Breakdown Limits in High-Vacuum X-Band Structures

    International Nuclear Information System (INIS)

    Dolgashev, Valery A.

    2003-01-01

    RF breakdown is one of the major factors determining performance of high power rf components and rf sources. RF breakdown limits working power and produces irreversible surface damage. The breakdown limit depends on the rf circuit, structure geometry, and rf frequency. It is also a function of the input power, pulse width, and surface electric and magnetic fields. In this paper we discuss multi-megawatt operation of X-band rf structures at pulse width on the order of one microsecond. These structures are used in rf systems of high gradient accelerators. Recent experiments at Stanford Linear Accelerator Center (SLAC) have explored the functional dependence of breakdown limit on input power and pulse width. The experimental data covered accelerating structures and waveguides. Another breakdown limit of accelerating structures was associated with high magnetic fields found in waveguide-to-structure couplers. To understand and quantify these limits we simulated 3D structures with the electrodynamics code Ansoft HFSS and the Particle-In-Cell code MAGIC3D. Results of these simulations together with experimental data will be discussed in this paper

  15. STATUS OF X-BAND STANDING WAVE STRUCTURE STUDIES AT SLAC

    International Nuclear Information System (INIS)

    Dolgashev, Valery A.

    2003-01-01

    The linacs proposed for the Next Linear Collider (NLC) and Japanese Linear Collider (JLC) would contain several thousand X-Band accelerator structures that would operate at a loaded gradient of 50 MV/m. An extensive experimental and theoretical program is underway at SLAC, FNAL and KEK to develop structures that reliably operate at this gradient. The development of standing wave structures is a part of this program. The properties of standing wave structures allow them to operate at the loaded gradient in contrast to traveling wave structures that need conditioning to the unloaded gradient (65 MV/m for NLC/JLC). The gradients in the standing structures tested thus far have been limited by input coupler breakdowns. The behavior of these breakdowns is consistent with a model of pulsed heating due to high magnetic fields. New input couplers have been designed to reduce maximum magnetic fields. This paper discusses design considerations related to high power performance, wakefield suppression and results of high power tests of prototype standing wave structures

  16. Wakefield and Beam Centering Measurements of a Damped and Detuned X-Band Accelerator Structure

    International Nuclear Information System (INIS)

    Adolphsen, Chris

    1999-01-01

    In the Next Linear Collider (NLC) design, X-Band (11.4 GHz) accelerator structures are used to accelerate multibunch beams to several hundred GeV. Although these structures allow for high gradient operation, their strong deflecting modes impose a number of operational constraints. In particular, the long-range transverse wakefields generated by the bunches need to be reduced by about two orders of magnitude to prevent significant beam breakup. During the past five years, a reduction scheme that employs both detuning and damping of the structure dipole modes has been developed to meet this requirement. Several prototype Damped and Detuned Structures (DDS) have been built to test and refine this scheme. The wakefield of the latest version, DDS3, has recently been measured in the Accelerator Structure Setup (ASSET) facility at SLAC. In this paper, we present these results together with predictions based on an equivalent circuit model of the structure. We also present ASSET studies in which the beam-induced dipole signals that are coupled out for damping purposes are used to center the beam in the structure

  17. Probing the unconventional superconducting state of LiFeAs by quasiparticle interference.

    Science.gov (United States)

    Hänke, Torben; Sykora, Steffen; Schlegel, Ronny; Baumann, Danny; Harnagea, Luminita; Wurmehl, Sabine; Daghofer, Maria; Büchner, Bernd; van den Brink, Jeroen; Hess, Christian

    2012-03-23

    A crucial step in revealing the nature of unconventional superconductivity is to investigate the symmetry of the superconducting order parameter. Scanning tunneling spectroscopy has proven a powerful technique to probe this symmetry by measuring the quasiparticle interference (QPI) which sensitively depends on the superconducting pairing mechanism. A particularly well-suited material to apply this technique is the stoichiometric superconductor LiFeAs as it features clean, charge neutral cleaved surfaces without surface states and a relatively high T(c)∼18  K. Our data reveal that in LiFeAs the quasiparticle scattering is governed by a van Hove singularity at the center of the Brillouin zone which is in stark contrast to other pnictide superconductors where nesting is crucial for both scattering and s(±) superconductivity. Indeed, within a minimal model and using the most elementary order parameters, calculations of the QPI suggest a dominating role of the holelike bands for the quasiparticle scattering. Our theoretical findings do not support the elementary singlet pairing symmetries s(++), s(±), and d wave. This brings to mind that the superconducting pairing mechanism in LiFeAs is based on an unusual pairing symmetry such as an elementary p wave (which provides optimal agreement between the experimental data and QPI simulations) or a more complex order parameter (e.g., s+id wave symmetry).

  18. Ballistic-electron-emission spectroscopy of AlxGa1-xAs/GaAs heterostructures: Conduction-band offsets, transport mechanisms, and band-structure effects

    International Nuclear Information System (INIS)

    OShea, J.J.; Brazel, E.G.; Rubin, M.E.; Bhargava, S.; Chin, M.A.; Narayanamurti, V.

    1997-01-01

    We report an extensive investigation of semiconductor band-structure effects in single-barrier Al x Ga 1-x As/GaAs heterostructures using ballistic-electron-emission spectroscopy (BEES). The transport mechanisms in these single-barrier structures were studied systematically as a function of temperature and Al composition over the full compositional range (0≤x≤1). The initial (Γ) BEES thresholds for Al x Ga 1-x As single barriers with 0≤x≤0.42 were extracted using a model which includes the complete transmission probability of the metal-semiconductor interface and the semiconductor heterostructure. Band offsets measured by BEES are in good agreement with previous measurements by other techniques which demonstrates the accuracy of this technique. BEES measurements at 77 K give the same band-offset values as at room temperature. When a reverse bias is applied to the heterostructures, the BEES thresholds shift to lower voltages in good agreement with the expected bias-induced band-bending. In the indirect band-gap regime (x>0.45), spectra show a weak ballistic-electron-emission microscopy current contribution due to intervalley scattering through Al x Ga 1-x As X valley states. Low-temperature spectra show a marked reduction in this intervalley current component, indicating that intervalley phonon scattering at the GaAs/Al x Ga 1-x As interface produces a significant fraction of thisX valley current. A comparison of the BEES thresholds with the expected composition dependence of the Al x Ga 1-x As Γ, L, and X points yields good agreement over the entire composition range. copyright 1997 The American Physical Society

  19. 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

  20. Quasiparticle Aggregation in the Fractional Quantum Hall Effect

    Science.gov (United States)

    Laughlin, R. B.

    1984-10-10

    Quasiparticles in the Fractional Quantum Hall Effect behave qualitatively like electrons confined to the lowest landau level, and can do everything electrons can do, including condense into second generation Fractional Quantum Hall ground states. I review in this paper the reasoning leading to variational wavefunctions for ground state and quasiparticles in the 1/3 effect. I then show how two-quasiparticle eigenstates are uniquely determined from symmetry, and how this leads in a natural way to variational wavefunctions for composite states which have the correct densities (2/5, 2/7, ...). I show in the process that the boson, anyon and fermion representations for the quasiparticles used by Haldane, Halperin, and me are all equivalent. I demonstrate a simple way to derive Halperin`s multiple-valued quasiparticle wavefunction from the correct single-valued electron wavefunction. (auth)