WorldWideScience

Sample records for crystal field splittings

  1. Crystal Field Splittings of NdN

    DEFF Research Database (Denmark)

    Warming, E.; Bak, Poul Erik

    1975-01-01

    The crystal field levels of the Nd (J=9/2) ion in NdN have been determined by inelastic neutron scattering. The crystal field parameters obtained by a least-squares fit to the spectra at 80K are: B4=-0.042+or-0.002K and B6=-0.00042+or-0.00002K. This result contrasts with the point charge model used...

  2. Longitudinal magnetoresistance of layered crystals in a quantizing magnetic field taking into account the spin splitting

    Science.gov (United States)

    Askerov, B. M.; Figarova, S. R.; Mahmudov, M. M.

    2006-07-01

    The magnetoresistance of layered crystals in a longitudinal quantizing magnetic field by taking into account the spin splitting is theoretically investigated. The general expression for the electrical conductivity of a quasi two-dimensional electron gas at the deformation-potential scattering has been obtained. In the behavior of the specific resistance, peaks have been revealed, and a number and positions of the peaks are dictated by the spin splitting magnitude.

  3. Capability of the free-ion eigenstates for crystal-field splitting

    CERN Document Server

    Mulak, Jacek

    2011-01-01

    Any electron eigenstate |\\Psi>of the paramagnetic ion open-shell is characterized by the three independent multipole asphericities A_{k}= for k=2,4 and 6 related to the second moments of the relevant crystal-field splittings by \\sigma_{k}^{2}=]A_{k}^{2}S_{k}^{2}, where S_{k}^{2}=]\\sum_{q}|B_{kq}|^{2}. The A_{k} can serve as a reliable measure of the state |\\Psi>capability for the splitting produced by the k-rank component of the crystal-field Hamiltonian and allow one to verify any fitted crystal-field parameter set directly comparing the calculated and the experimental second moments of the relevant crystal-field splittings. We present the multipole characteristics A_{k} for the extensive set of eigenstates from the lower parts of energy spectra of the tripositive 4f^{N} ions applying in the calculations the advanced eigenfunctions of the free lanthanide ions obtained based on the M. Reid f-shell programs. Such amended asphericities are compared with those achieved for the simplified Russell-Saunders states....

  4. First and second order numerical methods based on a new convex splitting for phase-field crystal equation

    Science.gov (United States)

    Shin, Jaemin; Lee, Hyun Geun; Lee, June-Yub

    2016-12-01

    The phase-field crystal equation derived from the Swift-Hohenberg energy functional is a sixth order nonlinear equation. We propose numerical methods based on a new convex splitting for the phase-field crystal equation. The first order convex splitting method based on the proposed splitting is unconditionally gradient stable, which means that the discrete energy is non-increasing for any time step. The second order scheme is unconditionally weakly energy stable, which means that the discrete energy is bounded by its initial value for any time step. We prove mass conservation, unique solvability, energy stability, and the order of truncation error for the proposed methods. Numerical experiments are presented to show the accuracy and stability of the proposed splitting methods compared to the existing other splitting methods. Numerical tests indicate that the proposed convex splitting is a good choice for numerical methods of the phase-field crystal equation.

  5. First and second order operator splitting methods for the phase field crystal equation

    Science.gov (United States)

    Lee, Hyun Geun; Shin, Jaemin; Lee, June-Yub

    2015-10-01

    In this paper, we present operator splitting methods for solving the phase field crystal equation which is a model for the microstructural evolution of two-phase systems on atomic length and diffusive time scales. A core idea of the methods is to decompose the original equation into linear and nonlinear subequations, in which the linear subequation has a closed-form solution in the Fourier space. We apply a nonlinear Newton-type iterative method to solve the nonlinear subequation at the implicit time level and thus a considerably large time step can be used. By combining these subequations, we achieve the first- and second-order accuracy in time. We present numerical experiments to show the accuracy and efficiency of the proposed methods.

  6. First and second order operator splitting methods for the phase field crystal equation

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyun Geun; Shin, Jaemin [Institute of Mathematical Sciences, Ewha Womans University, Seoul 120-750 (Korea, Republic of); Lee, June-Yub, E-mail: jyllee@ewha.ac.kr [Department of Mathematics, Ewha Womans University, Seoul 120-750 (Korea, Republic of)

    2015-10-15

    In this paper, we present operator splitting methods for solving the phase field crystal equation which is a model for the microstructural evolution of two-phase systems on atomic length and diffusive time scales. A core idea of the methods is to decompose the original equation into linear and nonlinear subequations, in which the linear subequation has a closed-form solution in the Fourier space. We apply a nonlinear Newton-type iterative method to solve the nonlinear subequation at the implicit time level and thus a considerably large time step can be used. By combining these subequations, we achieve the first- and second-order accuracy in time. We present numerical experiments to show the accuracy and efficiency of the proposed methods.

  7. Modulation of electrical mobility in Au ion irradiated titanium oxide with crystal field splitting

    Science.gov (United States)

    Park, Hyun-Woo; Jun, Byung-Hyuk; Choi, Dukhyun; Chung, Kwun-Bum

    2016-11-01

    Electrical modulation of radio frequency (RF) sputtered TiO2- x films were investigated as a function of Au swift heavy ion irradiation dose at room temperature. The prepared TiO2- x films were irradiated with 130 MeV Au swift heavy ion in the range from 1 × 1011 to 5 × 1012 ions/cm2. As the Au ion irradiation dose increased up to 1 × 1012 ions/cm2, the electrical mobility of TiO2- x films were dramatically increased 3.07 × 102 cm2 V-1 s-1 without the change of carrier concentration. These changes in electrical properties of Au irradiated TiO2- x film, are related to the modification of electronic structure such as crystal field splitting of Ti 3d orbital hybridization and sub-band edge states below the conduction band as a function of Au swift heavy ion irradiation dose.

  8. EMR-related problems at the interface between the crystal field Hamiltonians and the zero-field splitting Hamiltonians

    Directory of Open Access Journals (Sweden)

    Rudowicz Czesław

    2015-07-01

    Full Text Available The interface between optical spectroscopy, electron magnetic resonance (EMR, and magnetism of transition ions forms the intricate web of interrelated notions. Major notions are the physical Hamiltonians, which include the crystal field (CF (or equivalently ligand field (LF Hamiltonians, and the effective spin Hamiltonians (SH, which include the zero-field splitting (ZFS Hamiltonians as well as to a certain extent also the notion of magnetic anisotropy (MA. Survey of recent literature has revealed that this interface, denoted CF (LF ↔ SH (ZFS, has become dangerously entangled over the years. The same notion is referred to by three names that are not synonymous: CF (LF, SH (ZFS, and MA. In view of the strong need for systematization of nomenclature aimed at bringing order to the multitude of different Hamiltonians and the associated quantities, we have embarked on this systematization. In this article, we do an overview of our efforts aimed at providing a deeper understanding of the major intricacies occurring at the CF (LF ↔ SH (ZFS interface with the focus on the EMR-related problems for transition ions.

  9. An energy-stable convex splitting for the phase-field crystal equation

    KAUST Repository

    Vignal, P.

    2015-10-01

    Abstract The phase-field crystal equation, a parabolic, sixth-order and nonlinear partial differential equation, has generated considerable interest as a possible solution to problems arising in molecular dynamics. Nonetheless, solving this equation is not a trivial task, as energy dissipation and mass conservation need to be verified for the numerical solution to be valid. This work addresses these issues, and proposes a novel algorithm that guarantees mass conservation, unconditional energy stability and second-order accuracy in time. Numerical results validating our proofs are presented, and two and three dimensional simulations involving crystal growth are shown, highlighting the robustness of the method. © 2015 Elsevier Ltd.

  10. XPS Observations of Crystal Field Splitting in TiO2 Thin Films in Quantum Confinement Approach

    Science.gov (United States)

    Sushkova, Natalya

    2015-03-01

    Transition metal oxides attract increased interest due to amazing electrical and magnetic properties and their outstanding applications designated by relative d-band redistributions that are shifted in such a way that narrow bands arranged by localized electrons are situated in the vicinity of EF. Different kinds of lattice distortions caused by doping and/or quantum size confinement of TM oxides are assigned to remarkable phenomenon Mott metal-insulator transitions, when mutual metal-oxide orbital arrangement changes dramatically. There is a widespread consensus that strong electron correlations are responsible for that change and magnetic excitation is one of manifestations of these correlations. Here we are presenting XPS study of titanium dioxide nanocrystal formations on silicon substrate with native oxide. The dynamic changes in XPS spectra were used for analysis of TiO2 thin films with mass thicknesses up to 2 monolayers formed by redox reactions of sputtered Ti on Si(100) substrate with native oxide implemented in situ under UHV conditions. XPS spectra evolution, as a traditional source of information on phase composition, was complemented by the possibility to estimate the morphology and crystal field splitting of formed precipitates. Intensity fluctuations observed for O1s, Si 2p, Ti2p spectra were accompanied by crystal field splitting in Ti2p and on second derivatives of O1s. These fluctuations were followed by noticeable changes in the vicinity of band gap indicating possible Mott metal-insulator transitions.

  11. Crystal electric field and dimer splitting in Cs{sub 3}Er{sub 2}X{sub 9} (X=Cl, Br)

    Energy Technology Data Exchange (ETDEWEB)

    Allenspach, P.; Furrer, A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Guedel, H.U.; Furer, N. [Bern Univ. (Switzerland); Buettner, H. [Institut Max von Laue - Paul Langevin, 75 - Paris (France)

    1997-09-01

    Inelastic neutron scattering technique was used to measure the crystal electric field (CEF) splitting of Cs{sub 3}Er{sub 2}Cl{sub 9}. Besides a low lying magnetic excitation at around 2 meV all the other transitions are in agreement with CEF transitions found in optical measurements. Similar additional low-lying magnetic transitions were found in Cs{sub 3}Er{sub 2}Br{sub 9}. While excitations of the rare-earth dimers most likely play a role, the size of the splitting and its absence in optical spectra still remain a mystery. (author) 2 figs., 5 refs.

  12. Revealing the consequences and errors of substance arising from the inverse confusion between the crystal (ligand) field quantities and the zero-field splitting ones

    Energy Technology Data Exchange (ETDEWEB)

    Rudowicz, Czesław, E-mail: crudowicz@zut.edu.pl [Institute of Physics, West Pomeranian University of Technology, Al. Piastów 17, 70-310 Szczecin (Poland); Karbowiak, Mirosław [Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław (Poland)

    2015-01-01

    Survey of recent literature has revealed a doubly-worrying tendency concerning the treatment of the two distinct types of Hamiltonians, namely, the physical crystal field (CF), or equivalently ligand field (LF), Hamiltonians and the zero-field splitting (ZFS) Hamiltonians, which appear in the effective spin Hamiltonians (SH). The nature and properties of the CF (LF) Hamiltonians have been mixed up in various ways with those of the ZFS Hamiltonians. Such cases have been identified in a rapidly growing number of studies of the transition-ion based systems using electron magnetic resonance (EMR), optical spectroscopy, and magnetic measurements. These findings have far ranging implications since these Hamiltonians are cornerstones for interpretation of magnetic and spectroscopic properties of the single transition ions in various crystals or molecules as well as the exchange coupled systems (ECS) of transition ions, e.g. single molecule magnets (SMM) or single ion magnets (SIM). The seriousness of the consequences of such conceptual problems and related terminological confusions has reached a level that goes far beyond simple semantic issues or misleading keyword classifications of papers in journals and scientific databases. The prevailing confusion, denoted as the CF=ZFS confusion, pertains to the cases of labeling the true ZFS quantities as purportedly the CF (LF) quantities. Here we consider the inverse confusion between the CF (LF) quantities and the SH (ZFS) ones, denoted the ZFS=CF confusion, which consists in referring to the parameters (or Hamiltonians), which are the true CF (LF) quantities, as purportedly the ZFS (or SH) quantities. Specific cases of the ZFS=CF confusion identified in recent textbooks, reviews and papers, especially SMM- and SIM-related ones, are surveyed and the pertinent misconceptions are clarified. The serious consequences of the terminological confusions include misinterpretation of data from a wide range of experimental techniques and

  13. ISR split-field magnet

    CERN Multimedia

    1975-01-01

    The experimental apparatus used at intersection 4 around the Split-Field Magnet by the CERN-Bologna Collaboration (experiment R406). The plastic scintillator telescopes are used for precise pulse-height and time-of-flight measurements.

  14. Zero-field splitting and local structure for V2+ ions in CsMgX$_{3} (X=Cl, Br, I)$ crystals

    Indian Academy of Sciences (India)

    Q Wei; Q M Xu; Z Y Yang; D Y Zhang; J G Zhang

    2009-11-01

    The zero-field splitting and local structure for V2+ ions in CsMgX3 $(X = Cl, Br, I)$ crystals are theoretically investigated using complete diagonalization method (CDM) for a $3d^{3}$ ion in trigonal symmetry. Spin–spin (SS) and spin–other-orbit (SOO) interactions are taken into account in addition to the general spin–orbit (SO) interaction. On this basis, using ligand ion displacement model, we find that the ligand ions move away from $C_{3}$-axis, and therefore the local angles in the $V^{2+}$ centres are larger than the angles in the hosts. The results show good agreement with the observed values.

  15. Reversed Crystal-Field Splitting and Spin-Orbital Ordering in α-Sr2CrO4

    Science.gov (United States)

    Ishikawa, Takashi; Toriyama, Tatsuya; Konishi, Takehisa; Sakurai, Hiroya; Ohta, Yukinori

    2017-03-01

    The origin of successive phase transitions observed in the layered perovskite α-Sr2CrO4 is studied by the density-functional-theory-based electronic structure calculation and mean-field analysis of the proposed low-energy effective model. We find that, despite the fact that the CrO6 octahedron is elongated along the c-axis of the crystal structure, the crystal-field level of nondegenerate 3dxy orbitals of the Cr ion is lower in energy than that of doubly degenerate 3dyz and 3dxz orbitals, giving rise to the orbital degrees of freedom in the system with a 3d2 electron configuration. We show that the higher (lower) temperature phase transition is caused by the ordering of the orbital (spin) degrees of freedom.

  16. Magnetooptics of non-Kramers Eu3+ions in garnets:analysis complemented by crystal-field splitting modeling calculations

    Institute of Scientific and Technical Information of China (English)

    Uygun V.Valiev; John B.Gruber; Anvar K.Mukhammadiev; Vasiliy O.Pelenovich; FU Dejun; Gary W.Burdick

    2013-01-01

    Spectra of absorption, luminescence, magnetic circular dichroism (MCD), and magnetic circular polarization of lumines-cence (MCPL) in Gd3Ga5O12:Eu3+and Eu3Ga5O12 garnets were studied within the visible spectral range at 300 K. Analysis of the spectral and temperature dependences of the magnetooptical and optical spectra made it possible to identify the magneto-dipole (MD) and electro-dipole (ED) 4f→4f transitions occurring between Stark sublevels of the 7FJ (J=1, 2) and 5D0 multiplets in Eu3+-containing garnet structures. Quantum mechanical “mixing” had significant influence on quasi-degenerate states of the non-Kramers rare-earth Eu3+ion for Eu3Ga5O12 in MCD due to forbidden MD transition 7F1→5D0 and for Gd3Ga5O12:Eu3+in MCPL due to MD 4f→4f transition 5D0→7F1 and forced ED-transition 5D0→7F2. A parameterized Hamiltonian defined to operate within the entire 4f(6) ground electronic configuration of Eu3+ion was used to model the experimental Stark levels, including their irreducible rep-resentations and wavefunctions. The crystal-field parameters were determined through a Monte-Carlo method in which nine in-dependent crystal-field parameters, Bkq , were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental levels was 0.73 meV.

  17. Crystal field splitting of the 4f 5d electronic configuration of Pr 3+ ions in wide band gap fluoride dielectric crystals

    Science.gov (United States)

    Sarantopoulou, E.; Kollia, Z.; Cefalas, A. C.; Semashko, V. V.; Yu. Abdulsabirov, R.; Naumov, A. K.; Korableva, S. L.; Szczurek, T.; Kobe, S.; McGuiness, P. J.

    2002-07-01

    The absorption and the laser-induced fluorescence spectra of Pr 3+ ion in YF 3, LaF 3, KY 3 F 10 and LiLuF 4, single crystal hosts were obtained in the vacuum ultraviolet region of the spectrum. The energy position and the spacing of the levels of the 4f 5d electronic configuration depend on the host matrix. In addition, strong vacuum ultraviolet emission bands were observed, following crystal excitation at 157 nm with the molecular fluorine laser. The emission bands were due to the interconfigurational 4 f 5 d→4 f2 dipole-allowed transitions in Pr 3+ ions, and they were assigned to the transitions between the edge of the lowest Stark component of the 4f 5d electronic configuration and the levels of the 4f 2 electronic configuration. The VUV spectra can be interpreted by applying the crystal field model, and taking into consideration that lanthanide contraction of the 4f n-1 5d electronic configurations of the rare earth ions, and shielding of the positive ion charge from the electrons in the 4f n electronic configuration is taking place. Finally, a new method for monitoring the concentration of the rare earth ions in wide band gap fluoride dielectric crystals in a non-destructive way, by measuring magnetic dipole moments with the vibrating sample magnetometer (VSM) method, is presented for the first time to our knowledge for this type of crystals.

  18. Distinguishing division algebras by finite splitting fields

    CERN Document Server

    Krashen, Daniel

    2010-01-01

    This paper is concerned with the problem of determining the number of division algebras which share the same collection of finite splitting fields. As a corollary we are able to determine when two central division algebras may be distinguished by their finite splitting fields over certain fields.

  19. Degeneracy and Split of Defect States in Photonic Crystals

    Institute of Scientific and Technical Information of China (English)

    黄晓琴; 崔一平

    2003-01-01

    One-dimensional photonic crystals with two or more structural defects are studied. We observed an interesting characteristic of transmission band structure of photonic crystals with defects using the transmission-matrixmethod simulation. The transmission states in the wide photonic band gap caused by defects revealdegeneracy and split in certain conditions. Every split state is contributed by coupling of all defects in a photonic crystal.Using the tight-binding method, we obtain an approximate analytic expression for the split frequency of photonic crystals with two structural defects.

  20. Polarization beam splitting using a birefringent graded photonic crystal.

    Science.gov (United States)

    Cassan, Eric; Van Do, Khanh; Dellinger, Jean; Le Roux, Xavier; de Fornel, Frédérique; Cluzel, Benoit

    2013-02-15

    The use of a birefringent graded photonic crystal (GPhC) is proposed for the realization of an efficient polarization beam splitter. This approach allows decoupling the two functions of efficient light injection for both polarizations and TE/TM beam splitting. A smooth light polarization splitting is naturally achieved due to the different curved trajectories followed within the graded medium by the TE and TM waves. A 160 nm operating bandwidth with insertion loss around 1 dB and interpolarization crosstalk below -15 dB is predicted by a finite difference time domain simulation. The unusually exploited electromagnetic phenomena are experimentally evidenced by scanning near-field optical measurements performed on samples fabricated using the silicon on insulator photonics technology. These experimental works open perspectives for the use of birefringent GPhCs to manage polarization diversity in silicon photonic circuits.

  1. Multiple beam splitting in elastic phononic crystal plates.

    Science.gov (United States)

    Lee, Hyuk; Oh, Joo Hwan; Kim, Yoon Young

    2015-02-01

    This work presents an experimental evidence for triple beam splitting in an elastic plate with an embedded elastic phononic crystal (PC) prism and elaborates on its working mechanism. While there were reports on negative refraction and double beam splitting with PCs, no experimental evidence on the splitting of triple or more ultrasonic elastic beams through PCs has been shown yet. After the experimental results are presented in case of triple beam splitting, further analysis is carried out to explain how triple or more beams can be split depending on elastic PC prism angles. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Terminological confusions and problems at the interface between the crystal field Hamiltonians and the zero-field splitting Hamiltonians—Survey of the CF=ZFS confusion in recent literature

    Energy Technology Data Exchange (ETDEWEB)

    Rudowicz, Czesław, E-mail: crudowicz@zut.edu.pl [Institute of Physics, West Pomeranian University of Technology, Al. Piastów 17, 70-310 Szczecin (Poland); Karbowiak, Mirosław [Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław (Poland)

    2014-10-15

    The single transition ions in various crystals or molecules as well as the exchange coupled systems (ECS) of transition ions, especially the single molecule magnets (SMM) or molecular nanomagnets (MNM), have been extensively studied in recent decades using electron magnetic resonance (EMR), optical spectroscopy, and magnetic measurements. Interpretation of magnetic and spectroscopic properties of transition ions is based on two physically distinct types of Hamiltonians: the physical crystal field (CF), or equivalently ligand field (LF), Hamiltonians and the effective spin Hamiltonians (SH), which include the zero-field splitting (ZFS) Hamiltonians. Survey of recent literature has revealed a number of terminological confusions and specific problems occurring at the interface between these Hamiltonians (denoted CF (LF)↔SH (ZFS)). Elucidation of sloppy or incorrect usage of crucial notions, especially those describing or parameterizing crystal fields and zero field splittings, is a very challenging task that requires several reviews. Here we focus on the prevailing confusion between the CF (LF) and SH (ZFS) quantities, denoted as the CF=ZFS confusion, which consists in referring to the parameters (or Hamiltonians), which are the true ZFS (or SH) quantities, as purportedly the CF (LF) quantities. The inverse ZFS=CF confusion, which pertains to the cases of labeling the true CF (LF) quantities as purportedly the ZFS quantities, is considered in a follow-up paper. The two reviews prepare grounds for a systematization of nomenclature aimed at bringing order to the zoo of different Hamiltonians. Specific cases of the CF=ZFS confusion identified in the recent textbooks, review articles, and SMM (MNM)- and EMR-related papers are surveyed and the pertinent misconceptions are outlined. The consequences of the terminological confusions go far beyond simple semantic issues or misleading keyword classifications of papers in journals and scientific databases. Serious

  3. Crystal electric field splitting of R{sup 3+}-ions in pure and Co- and Cu-doped RNi{sub 2}B{sub 2}C (R=Ho, Er, Tm)

    Energy Technology Data Exchange (ETDEWEB)

    Gasser, U.; Allenspach, P.; Henggeler, W.; Zolliker, M.; Furrer, A. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-09-01

    From the crystal-electric-field (CEF) splitting of the R{sup 3+}-ions, the CEF parameters of RNi{sub 2}B{sub 2}C (R=Ho, Er, Tm) were deduced. In order to get information about the influence of the variation of the density of states (DOS) at the Fermi level (E{sub F}), CEF spectroscopy measurements with Co- and Cu-doped ErNi{sub 2}B{sub 2}C-samples were performed. (author) 1 fig., 1 tab., 1 ref.

  4. Crystal field splittings of PrX 2 compounds (X=Pt, Rh, Ir, Ru, Ni) studied by inelastic neutron scattering

    Science.gov (United States)

    Greidanus, F. J. A. M.; De Jongh, L. J.; Huiskamp, W. J.; Furrer, A.; Buschow, K. H. J.

    1983-01-01

    Neutron inelastic scattering experiments have been performed on polycrystalline samples of the cubic Laves phase compounds PrX 2(X=Pt, Rh, Ir, Ni). Measurements in the paramagnetic state yield LLW parameters 0.6< x<1 and W<0. In this region various levels cross at an x value 0.86 and as a consequence the electronic ground state in the paramagnetic regime is either the singlet Γ 1, or the non-magnetic doublet Γ 3. Measurements in the ferromagnetic state support these conclusions. The crystal-field parameters obtained can be used in model calculations of some macroscopic quantities, in particular the specific heat and the spontaneous magnetization. The variation of the x values in the present series of Laves phase compounds evidences the presence of a contribution by conduction electrons to the crystal field.

  5. Soft-x-ray linear-dichroism and magnetic-circular-dichroism studies of CeRh3B2: Large crystal-field splitting and anomalous ferromagnetism

    Science.gov (United States)

    Yamaguchi, K.; Namatame, H.; Fujimori, A.; Koide, T.; Shidara, T.; Nakamura, M.; Misu, A.; Fukutani, H.; Yuri, M.; Kasaya, M.; Suzuki, H.; Kasuya, T.

    1995-05-01

    CeRh3B2 shows an anomalously high Curie temperature (Tc=115 K) for a Ce compound with nonmagnetic constituents, strong anisotropy in the magnetic susceptibility, and ferromagnetic ordering. We have studied its electronic structure by measuring linear dichroism (LD) and magnetic circular dichroism (MCD) in the Ce 4d core-level x-ray-absorption spectra. The result for LD indicates a highly anisotropic distribution of Ce 4f electrons along the hexagonal c axis, while the MCD result shows that the magnetic moment of the Ce 4f electron is dominated by the orbital moment as in the case of a small crystal field. Using the Anderson-impurity model including the axial crystal field, the strong interatomic Ce 4f-Ce 5d hybridization and the Ce 4f-Rh 4d hybridization, we show that there is a range of parameter sets for the axial crystal field and the Ce 4f-valence-band transfer integral which explains the results of the LD and MCD experiments. Using the same parameter set, we have also attempted to explain the Kondo temperature and the unusually high Curie temperature.

  6. Crystal Splitting in the Growth of Bi2S3

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Jing; Alivisatos, A. Paul

    2006-06-15

    Novel Bi{sub 2}S{sub 3} nanostructures with a sheaf-like morphology are obtained via reaction of bismuth acetate-oleic acid complex with elemental sulfur in 1-octadecence. We propose these structures form by the splitting crystal growth mechanism, which is known to account for the morphology some mineral crystals assume in nature. By controlling the synthetic parameters, different forms of splitting, analogous to observed in minerals, are obtained in our case of Bi{sub 2}S{sub 3}. These new and complex Bi{sub 2}S{sub 3} nanostructures are characterized by TEM, SEM, XRD and ED.

  7. Crystal-field effects in fluoride crystals for optical refrigeration

    Energy Technology Data Exchange (ETDEWEB)

    Hehlen, Markus P [Los Alamos National Laboratory

    2010-01-01

    thermal energy from the solid and carries it away as high-entropy light, thereby cooling the material. In the ideal case, the respective laser-cooling power is given by the pump wavelength ({lambda}{sub p}), the mean fluorescence wavelength ({bar {lambda}}{sub L}), and the absorption coefficient (a{sub r}) of the pumped transition. These quantities are solely determined by crystal field interactions. On one hand, a large crystal-field splitting offers a favorably large difference of {lambda}{sub p} - {bar {lambda}}{sub L} and thus a high cooling efficiency {eta}{sub cool} = ({lambda}{sub p} - {bar {lambda}}{sub L})/{bar {lambda}}{sub L}. On the other hand, a small crystal-field splitting offers a high thermal population (n{sub i}) of the initial state of the pumped transition, giving a high pump absorption coefficient and thus high laser cooling power, particularly at low temperatures. A quantitative description of crystal-field interactions is therefore critical to the understanding and optimization of optical refrigeration. In the case of Yb3+ as the laser cooling ion, however, development of a crystal-field model is met with substantial difficulties. First, Yb3+ has only two 4/multiplets, {sup 2}F{sub 7/2} and {sup 2}F{sub 5/2}, which lead to at most 7 crystal-field levels. This makes it difficult, and in some cases impossible, to evaluate the crystal-field Hamiltonian, which has at least 4 parameters for any Yb3+ point symmety lower than cubic. Second, {sup 2}F{sub 7/2}{leftrightarrow}{sup 2}F{sub 5/2} transitions exhibit an exceptionally strong electron-phonon coupling compared to 4f transitions of other rare earths. This makes it difficult to distinguish electronic from vibronic transitions in the absorption and luminescence spectra and to reliably identify the crystal-field levels. Yb3+ crystal-field splittings reported in the literature should thus generally be viewed with caution. This paper explores the effects of crystal-field interactions on the laser cooling

  8. A variable temperature EPR study of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) single crystal at 170 GHz: zero-field splitting parameter and its absolute sign.

    Science.gov (United States)

    Misra, Sushil K; Andronenko, Serguei I; Chand, Prem; Earle, Keith A; Paschenko, Sergei V; Freed, Jack H

    2005-06-01

    EPR measurements have been carried out on a single crystal of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) at 170-GHz in the temperature range of 312-4.2K. The spectra have been analyzed (i) to estimate the spin-Hamiltonian parameters; (ii) to study the temperature variation of the zero-field splitting (ZFS) parameter; (iii) to confirm the negative absolute sign of the ZFS parameter unequivocally from the temperature-dependent relative intensities of hyperfine sextets at temperatures below 10K; and (iv) to detect the occurrence of a structural phase transition at 4.35K from the change in the structure of the EPR lines with temperature below 10K.

  9. Split-Field Magnet facility upgraded

    CERN Multimedia

    1977-01-01

    The Split Field Magnet (SFM) was the largest spectrometer for particles from beam-beam collisions in the ISR. It could determine particle momenta in a large solid angle, but was designed mainly for the analysis of forward travelling particles.As the magnet was working on the ISR circulating beams, its magnetic field had to be such as to restore the correct proton orbit.The SFM, therefore, produced zero field at the crossing point and fields of opposite signs upstream and downstream of it and was completed by 2 large and 2 small compensator magnets. The gradient effects were corrected by magnetic channels equipped with movable flaps. The useful magnetic field volume was 28 m3, the induction in the median plane 1.14 T, the gap heigth 1.1 m, the length 10.5 m, the weight about 1000 ton. Concerning the detectors, the SFM was the first massive application of multiwire proportional chambers (about 70000 wires) which filled the main and the large compensator magnets. In 1976 an improved programme was started with tw...

  10. Field-Split Preconditioned Inexact Newton Algorithms

    KAUST Repository

    Liu, Lulu

    2015-06-02

    The multiplicative Schwarz preconditioned inexact Newton (MSPIN) algorithm is presented as a complement to additive Schwarz preconditioned inexact Newton (ASPIN). At an algebraic level, ASPIN and MSPIN are variants of the same strategy to improve the convergence of systems with unbalanced nonlinearities; however, they have natural complementarity in practice. MSPIN is naturally based on partitioning of degrees of freedom in a nonlinear PDE system by field type rather than by subdomain, where a modest factor of concurrency can be sacrificed for physically motivated convergence robustness. ASPIN, originally introduced for decompositions into subdomains, is natural for high concurrency and reduction of global synchronization. We consider both types of inexact Newton algorithms in the field-split context, and we augment the classical convergence theory of ASPIN for the multiplicative case. Numerical experiments show that MSPIN can be significantly more robust than Newton methods based on global linearizations, and that MSPIN can be more robust than ASPIN and maintain fast convergence even for challenging problems, such as high Reynolds number Navier--Stokes equations.

  11. Crystal fields in UO2 - revisited

    Energy Technology Data Exchange (ETDEWEB)

    Nakotte, Heinz [Los Alamos National Laboratory; Rajatram, R [NMSU/UNIV OF N.C.; Kern, S [COLORADO STATE UNIV; Mcqueeney, R J [AMES LAB; Lander, G H [EUROPEAN COMMISIONS, JRC; Robinson, R A [BRAGG INSTITUTE

    2009-01-01

    We performed inelastic neutron scattering (INS) in order to re-investigate the crystal-field ground state and the level splitting in UO{sub 2}. Previous INS studies on UO{sub 2} by Amorelli et al. [Physical Review B 15, 1989, 1856] uncovered four excitations at low temperatures in the 150-180 meV range. Considering the dipole-allowed transitions, only three of these transitions could be explained by the published crystal-field model. Our INS results on a different UO{sub 2} sample revealed that the unaccounted peak at about 180 meV is a spurious one, and thus not intrinsic to UO{sub 2}. In good agreement with Amoretti's results, we corroborated that the ground-state of UO{sub 2} is the {Lambda}{sub 5} triplet, and we computed that the fourth- and six-order crystal field parameters are V{sub 4} = -116 meV and V{sub 6} = 26 meV, respectively. We also studied the INS response of the non-magnetic U{sub 0.4}Th{sub 0.6}O{sub 2}. The splitting for this thorium-doped compound is similar to the one of UO{sub 2}, which orders antiferromagnetically at low temperatures. Therefore, we can conclude that magnetic interactions only weakly perturb the energy level splitting, which is dominated by strong crystal fields.

  12. Mechanically tunable photonic crystal split-beam nanocavity

    Science.gov (United States)

    Lin, Tong; Zou, Yongchao; Zhou, Guangya; Chau, Fook Siong; Deng, Jie

    2016-03-01

    Photonic crystal split-beam nanocavities allow for ultra-sensitive optomechanical transductions but are degraded due to their relatively low optical quality factors. We report our recent work in designing a new type of one-dimensional photonic crystal split-beam nanocavity optimized for an ultra-high optical quality factor. The design is based on the combination of the deterministic method and hill-climbing algorithm. The latter is the simplest and most straightforward method of the local search algorithm, which provides the local maximum of the chosen quality factors. This split-beam nanocavity is made up of two mechanical uncoupled cantilever beams with Bragg mirrors patterned onto it and separated by a 75 nm air gap. Experimental results emphasize that the quality factor of the second order TE mode can be as high as 19,900. Additionally, one beam of the device is actuated in the lateral direction with the aid of a NEMS actuator and the quality factor maintains quite well even there's a lateral offset up to 64 nm. We also apply Fano resonance to further increase the Q-factor by constructing two interfering channels. Before tuning, the original Q-factor is 60,000; it's noteworthy that the topmost Q-factor reaches 67,000 throughout out-of-plane electrostatic force tuning. The dynamic mechanical modes of two devices is analyzed as well. Potentially promising applications, such as ultra-sensitive optomechanical torque sensor, local tuning of fano resonance, all-optical-reconfigurable filters etc, are foreseen.

  13. About the splitting field for rational valued characters

    Directory of Open Access Journals (Sweden)

    Ion Armeanu

    1994-05-01

    Full Text Available The problem of finding the splitting field for group characters is very old and important (see [4], Chapter 9. The most part of the papers on this subject are concerned with all irreducible characters of a group under certain conditions. It seems more difficult to obtain minimal splitting fields for only one character without strong conditions about the group. In this case, naturally,the number theoretical methods play an essential role. This paper concerns to prove that under certain circumstances if a rational character of a group has Q(21/2,i as splitting field, then Q(i or even Q(21/2 are splitting fields too.

  14. Compensation of Dipolar-Exciton Spin Splitting in Magnetic Field

    OpenAIRE

    Gorbunov, A. V.; Timofeev, V. B.

    2012-01-01

    Magnetoluminescence of spatially indirect dipolar excitons collected in 25 nm GaAs/AlGaAs single quantum well within a lateral potential trap has been studied in perpendicular magnetic field in Faraday geometry. The paramagnetic spin splitting of the luminescence line of the heavy-hole excitons in the trap centre is completely compensated at magnetic fields below critical value, around 2 Tesla. The effect of spin-splitting compensation is caused by the exchange interaction in dense exciton Bo...

  15. Zero-field splitting of 4T2 term for 3d3 ions in tetragonal symmetry

    Indian Academy of Sciences (India)

    Qun Wei; Qi-Ming Xu

    2009-04-01

    By taking into account slight interactions, i.e. spin-spin, spin-other-orbit and orbit-orbit interactions, in addition to spin-orbit interaction, the zero-field splitting of 4T2 state for 3d3 ions at tetragonal symmetry has been studied. The convergence of the approximation perturbation formula of 4T2 state for 3d3 ions at tetragonal symmetry has been investigated, and the contributions to zero-field splitting arising from magnetic interaction and tetragonal crystal field are discussed. It is found that there exists combined mechanism between magnetic interactions and tetragonal crystal field.

  16. Crystal field effects in TmCu2 compound

    Science.gov (United States)

    Zajac, Š.; Šíma, V.; Smetana, Z.

    1987-01-01

    The splitting of the3H6 multiplet has been estimated for the Tm3+ ion in the crystal electric field of the orthorhombic TmCu2 compound. Using the energy levels and appropriate eigenfunctions the crystal field only susceptibility has been calculated along the principal orthorhombic axes at temperatures 10 to 300 K. The obtained results are compared with our measurements of specific heat and paramagnetic susceptibility on polycrystalline sample.

  17. Bent crystal channeling applications for beam splitting, extraction and collimation in the U-70 accelerator of IHEP

    Energy Technology Data Exchange (ETDEWEB)

    Chesnokov, Yu.A., E-mail: chesnokov@ihep.ru; Afonin, A.G.; Baranov, V.T.; Britvich, G.I.; Chirkov, P.N.; Maisheev, V.A.; Terekhov, V.I.; Yazynin, I.A.

    2013-08-15

    The report presents an overview of the results of IHEP activity obtained during 1987-2012 in the field of studying and using bent crystals to steer high-energy particle beams. The hardware installed to study crystal beam splitting, collimation and extraction is described. It has been shown that the developed crystal deflectors are capable for sustaining long-term operation to deliver high-energy extracted beams for fixed-target physics. The first results on extraction of 24.1 GeV/nucleon carbon ions are also presented.

  18. Dynamics and control of fast ion crystal splitting in segmented Paul traps

    CERN Document Server

    Kaufmann, H; Schmiegelow, C T; Schmidt-Kaler, F; Poschinger, U G

    2014-01-01

    We theoretically investigate the process of splitting two-ion crystals in segmented Paul traps, i.e. the structural transition from two ions confined in a common well to ions confined in separate wells. The precise control of this process by application of suitable voltage ramps to the trap segments is non-trivial, as the harmonic confinement transiently vanishes during the process. This makes the ions strongly susceptible to background electric field noise, and to static offset fields in the direction of the trap axis. We analyze the reasons why large energy transfers can occur, which are impulsive acceleration, the presence of residual background fields and enhanced anomalous heating. For the impulsive acceleration, we identify the diabatic and adiabatic regimes, which are characterized by different scaling behavior of the energy transfer with respect to time. We propose a suitable control scheme based on experimentally accessible parameters. Simulations are used to verify both the high sensitivity of the s...

  19. Splitting fields of elements in arithmetic groups

    CERN Document Server

    Gorodnik, Alex

    2011-01-01

    We prove that the number of unimodular integral matrices in a norm ball whose characteristic polynomial has Galois group different than the full symmetric group is of strictly lower order of magnitude than the number of all such matrices in the ball, as the radius increases. More generally, we prove a similar result for the Galois groups associated with elements in any connected semisimple linear algebraic group defined and simple over a number field $F$. Our method is based on the abstract large sieve method developed by Kowalski, and the study of Galois groups via reductions modulo primes developed by Jouve, Kowalski and Zywina. The two key ingredients are a uniform quantitative lattice point counting result, and a non-concentration phenomenon for lattice points in algebraic subvarieties of the group variety, both established previously by the authors. The results answer a question posed by Rivin and by Jouve, Kowalski and Zywina, who have considered Galois groups of random products of elements in algebraic...

  20. Theoretical calculation of zero field splitting parameters of Cr{sup 3+} doped ammonium oxalate monohydrate

    Energy Technology Data Exchange (ETDEWEB)

    Kripal, Ram, E-mail: ram_kripal2001@rediffmail.com; Yadav, Awadhesh Kumar, E-mail: aky.physics@gmail.com

    2015-06-15

    Zero field splitting parameters (ZFSPs) D and E of Cr{sup 3+} ion doped ammonium oxalate monohydrate (AOM) are calculated with formula using the superposition model. The theoretically calculated ZFSPs for Cr{sup 3+} in AOM crystal are compared with the experimental value obtained by electron paramagnetic resonance (EPR). Theoretical ZFSPs are in good agreement with the experimental ones. The energy band positions of optical absorption spectra of Cr{sup 3+} in AOM crystal calculated with CFA package are in good match with the experimental values.

  1. Density functional theory of the crystal field in dioxides

    Science.gov (United States)

    Diviš, M.; Kuriplach, J.; Richter, M.; Steinbeck, L.

    1996-04-01

    Presented are the results of ab-initio density functional calculations for PrO2 and UO2 using the general potential LAPW and optimized LCAO method in the local density approximation. The crystal field splitting of ionic Pr4+ and U4+ ground states was calculated and compared with predictions of a superposition model.

  2. Calculation of the zero-field splitting D and g(perp)parameters in EPR for d3 spin systems in strong and moderate axial fields

    NARCIS (Netherlands)

    Kool, Th.W.; Bollegraaf, B.

    2010-01-01

    Numerical and analytical methods are used to investigate the calculation of the zero field splitting |2D| and g(perp) parameters in EPR for octahedrally surrounded d3 spin systems (S = 3/2) in strong and moderate axial crystal fields (|D|>=h{\

  3. Split Field magnet at the I4 ISR intersection

    CERN Multimedia

    1974-01-01

    The Split-Field Magnet (SFM) at I4 had an unconventional topology, consisting of two dipole magnets of opposite polarity. It formed the heart of the first general facility at the ISR. It had a useful magnetic field volume of 28 m3 and a field in the median plane of 1.14 T. With a gap height of 1.1 m and length of 10.5 m, the magnet weighed about 1000 t. The SFM spectrometer featured the first large-scale application of MWPCs (about 70,000 wires), which filled the main magnet, visible here in 1974, and the two large compensator magnets.

  4. Splitting of a high-energy positively-charged particle beam with a bent crystal

    Science.gov (United States)

    Bandiera, L.; Kirillin, I. V.; Bagli, E.; Berra, A.; De Salvador, D.; Guidi, V.; Lietti, D.; Mazzolari, A.; Prest, M.; Shul'ga, N. F.; Sytov, A.; Vallazza, E.

    2017-07-01

    The possibility of high-energy positively-charged particle beam splitting by means of a short bent axially oriented silicon crystal was recently reported in an experiment carried out at CERN SPS H8 extracted line with a 400 GeV/c proton beam. Here, we investigate more deeply such a possibility focusing our attention on the efficiency of beam splitting and its modulation for different crystal-to-beam orientations. New experimental results confirm the possibility of modulating the 400 GeV/c proton beam intensity in different planar channels by adjusting the orientation of the crystal. Furthermore, an analysis of the beam splitting efficiency vs. the curvature of the crystal was carried out through simulation, highlighting that there exists a bending radius for which the efficiency is maximal.

  5. Model (1:10) of the Split-Field Magnet

    CERN Multimedia

    1977-01-01

    The photo shows Klaus Brand from the ISR BOM group with the working model of the Split-Field Magnet, while setting up the field measuring bench. The bench used Hall probes for which he had developed the electronics instrumentation (ISR-BOM Int. Note 12-01-1977). The SFM model made of mild steel with copper coils had been measured in the years 1969-1970. This new mapping campaign was related to the installation of a large calorimeter to one side of the magnet.

  6. Application of ZnO single crystals for light-induced water splitting under UV irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Suhak, Yuriy, E-mail: suhak@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Izdebska, Katarzyna; Skupiński, Paweł; Wierzbicka, Aleksandra; Reszka, Anna; Sybilski, Piotr; Kowalski, Bogdan J.; Mycielski, Andrzej; Zytkiewicz, Zbigniew R. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Soszko, Michał [Industrial Chemistry Research Institute, Rydygiera 8, 01-793 Warsaw (Poland); Suchocki, Andrzej [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Institute of Physics, University of Bydgoszcz, Weyssenhoffa 11, 85-072 Bydgoszcz (Poland)

    2014-02-14

    This paper presents experimental results of implementation of ZnO single crystals as photoanodes in photoelectrochemical (PEC) cells for hydrogen generation through the process of water splitting. Both, as-grown and O{sub 2}-annealed ZnO single crystals were investigated for this purpose. A 351 nm argon laser line was used as the light source. The XRD investigations showed that used ZnO crystals are of good crystalline quality. It was found that the as-grown ZnO single crystals possess higher conversion efficiencies comparing to the O{sub 2}-annealed one. The photocurrent density was found to increase significantly with the increase of external bias applied and excitation light intensity. Time dependent photocurrent density characteristics showed that the decay of photocurrent density was not observed within the measurement time. The differences in behaviour of the as-grown and the annealed in O{sub 2} ZnO single crystals are discussed in terms of crystals intrinsic defects. - Highlights: • ZnO single crystals show excellent performance as photoanodes for water splitting. • ZnO single crystals showed good stability in aqueous solution. • Mid-gap band state introduction does not influence the efficiency of water splitting.

  7. Determination of three-dimensional strain state in crystals using self-interfered split HOLZ lines

    Energy Technology Data Exchange (ETDEWEB)

    Herring, Rodney, E-mail: rherring@uvic.ca [CAMTEC, MENG, University of Victoria, British Columbia, Canada V8W 2Y2 (Canada); Norouzpour, Mana [CAMTEC, MENG, University of Victoria, British Columbia, Canada V8W 2Y2 (Canada); Saitoh, Koh; Tanaka, Nobuo; Tanji, Takayoshi [EcoTopia, Nagoya University, Nagoya 461-8603 (Japan)

    2015-09-15

    An experimental method to measure the strain through the thickness of a crystal is demonstrated. This enables the full three-dimensional stress–strain state of a crystal at the nanoscale to be determined taking the current practice from two-dimensional strain state determination. Knowing the 3D strain state is desired by crystal growers in order to improve their crystal's quality. This method involves combining electron diffraction with electron interferometry in a transmission electron microscope. The electron diffraction uses a split higher order Laue zone (HOLZ) line and the electron interferometry uses an electron biprism.

  8. Splitting fields and periods of Fibonacci sequences modulo primes

    CERN Document Server

    Gupta, Sanjai; Su, Francis Edward

    2009-01-01

    What is the period of the Fibonacci sequence modulo a prime? The purpose of our brief expository paper is to illustrate an accessible, motivated treatment of this classical topic using only ideas from linear and abstract algebra (rather than the case-by-case analysis found in many papers on the subject, or techniques from graduate number theory). Our methods extend to general recurrences with prime moduli and provide some new insights. And our treatment highlights a nice application of the use of splitting fields that might be suitable to present in undergraduate course in abstract algebra or Galois theory.

  9. Splitting and biopsy for bovine embryo sexing under field conditions.

    Science.gov (United States)

    Lopes, R F; Forell, F; Oliveira, A T; Rodrigues, J L

    2001-12-01

    Improvements on embryo micromanipulation techniques led to the use of embryo bisection technology in commercial embryo transfer programs, and made possible the direct genetic analysis of preimplantation bovine embryos by biopsy. For example, aspiration and microsection, allow bovine embryos sexing by detection of male-specific Y-chromosome in a sample of embryonic cells. We report on the application of the methodologies of splitting and biopsy of bovine embryos in field conditions, and on the results of embryo sex determination by the polymerase chain reaction (PCR). Pregnancy rates achieved with fresh bisected or biopsied embryos (50 to 60%) were similar to the fresh intact embryos (55 to 61%). The PCR protocol used for embryo sexing showed 92% to 94% of efficiency and 90 to 100% of accuracy. These results demonstrate these procedures are suitable for use in field conditions.

  10. The effective crystal field potential

    CERN Document Server

    Mulak, J

    2000-01-01

    As it results from the very nature of things, the spherical symmetry of the surrounding of a site in a crystal lattice or an atom in a molecule can never occur. Therefore, the eigenfunctions and eigenvalues of any bound ion or atom have to differ from those of spherically symmetric respective free ions. In this way, the most simplified concept of the crystal field effect or ligand field effect in the case of individual molecules can be introduced. The conventional notion of the crystal field potential is narrowed to its non-spherical part only through ignoring the dominating spherical part which produces only a uniform energy shift of gravity centres of the free ion terms. It is well understood that the non-spherical part of the effective potential "seen" by open-shell electrons localized on a metal ion plays an essential role in most observed properties. Light adsorption, electron paramagnetic resonance, inelastic neutron scattering and basic characteristics derived from magnetic and thermal measurements, ar...

  11. Hidden local symmetry of Eu{sup 3+} in xenotime-like crystals revealed by high magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Han, Yibo; Ma, Zongwei; Zhang, Junpei; Wang, Junfeng; Du, Guihuan; Xia, Zhengcai; Han, Junbo, E-mail: junbo.han@mail.hust.edu.cn; Li, Liang [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Yu, Xuefeng [Department of Physics, Key Laboratory of Artificial Micro- and Nanostructures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China)

    2015-02-07

    The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu{sup 3+} sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO{sub 4}:Eu{sup 3+} crystal, which resulted from the alignment of Gd{sup 3+} magnetic moment in high magnetic fields; and a hexagonally symmetric local crystal fields was observed in the YPO{sub 4} nanocrystals at the Eu{sup 3+} sites characterized by the special axial and rhombic crystal field terms. These distinct Zeeman splitting behaviors uncover the crystal fields-related local symmetry of luminescent Eu{sup 3+} centers in different hosts or magnetic environments, which are significant for their applications in optics and optoelectronics.

  12. Single-Crystal Semiconductors with Narrow Band Gaps for Solar Water Splitting.

    Science.gov (United States)

    Wang, Tuo; Gong, Jinlong

    2015-09-07

    Solar water splitting provides a clean and renewable approach to produce hydrogen energy. In recent years, single-crystal semiconductors such as Si and InP with narrow band gaps have demonstrated excellent performance to drive the half reactions of water splitting through visible light due to their suitable band gaps and low bulk recombination. This Minireview describes recent research advances that successfully overcome the primary obstacles in using these semiconductors as photoelectrodes, including photocorrosion, sluggish reaction kinetics, low photovoltage, and unfavorable planar substrate surface. Surface modification strategies, such as surface protection, cocatalyst loading, surface energetics tuning, and surface texturization are highlighted as the solutions.

  13. Tuning the pseudo-Zeeman splitting in graphene cones by magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Kandemir, B.S.; Akay, D.

    2015-06-15

    The effect of a homogeneous magnetic field on the energy spectrum of gapped graphene cones with long range charged Coulomb impurity is investigated within the framework of the perturbation theory. It is found that, besides lifting the degeneracy of angular momentum channels due to topological defects, the size of the corresponding splitting is enhanced by the introduction of a homogeneous magnetic field. This indicates that the level splitting may be controlled by the strength of a magnetic field in topological cones. Therefore, our results show that the magnetic field may be used as a tool to tune the pseudo-Zeeman splitting in graphene cones. - Highlights: • The size of level splitting in angular momentum channels is enhanced by introduction of a homogenous magnetic field. • Pseudo-Zeeman splitting in graphene can be controlled by hydrogenic impurities. • Pseudo-Zeeman splitting may be controlled by the strength of magnetic field in topological cones.

  14. Beam-splitting code for light scattering by ice crystal particles within geometric-optics approximation

    Science.gov (United States)

    Konoshonkin, Alexander V.; Kustova, Natalia V.; Borovoi, Anatoli G.

    2015-10-01

    The open-source beam-splitting code is described which implements the geometric-optics approximation to light scattering by convex faceted particles. This code is written in C++ as a library which can be easy applied to a particular light scattering problem. The code uses only standard components, that makes it to be a cross-platform solution and provides its compatibility to popular Integrated Development Environments (IDE's). The included example of solving the light scattering by a randomly oriented ice crystal is written using Qt 5.1, consequently it is a cross-platform solution, too. Both physical and computational aspects of the beam-splitting algorithm are discussed. Computational speed of the beam-splitting code is obviously higher compared to the conventional ray-tracing codes. A comparison of the phase matrix as computed by our code with the ray-tracing code by A. Macke shows excellent agreement.

  15. Vacuum Rabi splitting with a single quantum dot in a photonic crystal nanocavity

    Science.gov (United States)

    Yoshie, T.; Scherer, A.; Hendrickson, J.; Khitrova, G.; Gibbs, H. M.; Rupper, G.; Ell, C.; Shchekin, O. B.; Deppe, D. G.

    2004-11-01

    Cavity quantum electrodynamics (QED) systems allow the study of a variety of fundamental quantum-optics phenomena, such as entanglement, quantum decoherence and the quantum-classical boundary. Such systems also provide test beds for quantum information science. Nearly all strongly coupled cavity QED experiments have used a single atom in a high-quality-factor (high-Q) cavity. Here we report the experimental realization of a strongly coupled system in the solid state: a single quantum dot embedded in the spacer of a nanocavity, showing vacuum-field Rabi splitting exceeding the decoherence linewidths of both the nanocavity and the quantum dot. This requires a small-volume cavity and an atomic-like two-level system. The photonic crystal slab nanocavity-which traps photons when a defect is introduced inside the two-dimensional photonic bandgap by leaving out one or more holes-has both high Q and small modal volume V, as required for strong light-matter interactions. The quantum dot has two discrete energy levels with a transition dipole moment much larger than that of an atom, and it is fixed in the nanocavity during growth.

  16. Symmetry Breaking and Fine Structure Splitting in Zincblende Quantum Dots: Atomistic Simulations of Long-Range Strain and Piezoelectric Field

    Science.gov (United States)

    Ahmed, Shaikh; Usman, Muhammad; Heitzinger, Clemens; Rahman, Rajib; Schliwa, Andrei; Klimeck, Gerhard

    2007-04-01

    Electrons and holes captured in self-assembled quantum dots (QDs) are subject to symmetry breaking that cannot be represented in with continuum material representations. Atomistic calculations reveal symmetry lowering due to effects of strain and piezo-electric fields. These effects are fundamentally based on the crystal topology in the quantum dots. This work studies these two competing effects and demonstrates the fine structure splitting that has been demonstrated experimentally can be attributed to the underlying atomistic structure of the quantum dots.

  17. Microscopic mechanism of the zero-field splitting parameters for 6S(3d5 ) state ions at trigonal symmetry crystal filed%三角对称晶场中6S(3d5)态离子零场分裂参量的微观起源

    Institute of Scientific and Technical Information of China (English)

    杨子元

    2011-01-01

    基于完全对角化方法(complete diagonalization method,CDM),研究了6S(3d5)态离子在三角晶场(包括C3v,D3,D3d点群对称晶场)中零场分裂(zero-field splitting,ZFS)参量D和(a-F)的微观起源.研究中除了考虑研究者通常考虑的SO(spin-orbit)磁相互作用外,同时考虑了SS(spin-spin),SOO(spin-other-orbit),OO(orbit-orbit)磁相互作用.研究表明:在三角对称晶场中,6S(3d5)态离子的ZFS参量在所选晶场的大多部分区域主要起源于SO机理,但SS机理、SOO机理、OO机理对ZFS参量的贡献不能被忽略.此外研究表明:ZFS参量D和(a-f)主要来自纯自旋四重态及自旋二重态与自旋四重态联合作用的贡献,纯自旋二重态对ZFS参量D和(a-F)的贡献为零.我们发现二阶ZFS参量D与四阶ZFS参量(a-f)有不同的微观起源.二阶ZFS参量D主要来自自旋四重态的贡献,而四阶ZFS参量(a-f)主要来自自旋二重态与自旋四重态联合作用的贡献.作为本文理论的应用,研究了掺杂晶体材料Fe3+:Al2O3,理论与实验测量符合很好.%The microscopic mechanism of the zero-field splitting parameters (ZFS) including D and (a - F) for 6S(3d5) state ion in trigonal-symmetry crystal field have been investigated using the complete diagonaliztion method (CDM) by taking into account the spin-spin (SS) , the spin-other-orbit (SOO) and the orbit-orbit (OO) magnetic interactions besides the well-known spin-orbit (SO) magnetic interaction.It was found that the contribution to the ZFS parameters D and (a -F)arising from the spin-orbit (SO) magnetic interaction is the most important in most of the crystal field (CF) ranges, but the contribution to the zero-field splitting (ZFS) parameter D and ( a - F) from the other three mechanisms, including the SS mechanism, SOO mechanism and OO mechanism, can't be ignored.The ZFS parameters D and (a - F) arise from the net spin quartet states as well as the combined effects of the spin doublet states and the spin quartets

  18. Wide-angle beam splitting by use of positive-negative refraction in photonic crystals.

    Science.gov (United States)

    Luo, Ye; Zhang, Wei; Huang, Yidong; Zhao, Jianhui; Peng, Jiangde

    2004-12-15

    We present a positive-negative refraction effect in which, under certain conditions, an incident plane wave launched into a photonic crystal excites a positive-refracted Bloch wave and a negative-refracted Bloch wave simultaneously, both of which maintain the polarization. By utilizing this phenomenon, wide-angle beam splitting can be realized at the microscale level. Numerical simulations are employed to demonstrate this anomalous refraction behavior.

  19. Study of Rare Events at the Split Field Magnet

    CERN Multimedia

    2002-01-01

    The aim of the experiment is the study of full events associated with special, rare triggers using the almost 4 @p geometry of the improved Split Field Magnet (SFM) detector. Two triggers are used: a) a trigger on an electron produced around 90|0 with a transverse momentum p^t @$>$ 0.5 GeV/c; b) a trigger on very high p^t hadrons (p^t $>$ 5 GeV/c) at @Q @C 45|0, using the SFM chambers to define roads pointing to the interaction region. In the first case, the associated event will be studied to determine the origin of direct electron production in charmed particle production. In the second case, the production of jets or jet-like objects when a high p^t particle is produced in pp collisions will be investigated. To carry out this program, the detection system consists of : \\item a) An improved SFM detector chamber system and layout to detect more of the produced particles and to simplify the pattern recognition problem in multiparticle events. \\item b) An improved program chain for the analysis of SFM events, ...

  20. Possible splitting of deconfinement and chiral transitions in strong magnetic fields in QCD

    CERN Document Server

    Fraga, Eduardo S; Chernodub, M N

    2010-01-01

    We show that finite-temperature deconfinement and chiral transitions can split in a strong enough magnetic field. The splitting in critical temperatures of these transitions in a constant magnetic field of a typical LHC magnitude is of the order of 10 MeV. A new deconfined phase with broken chiral symmetry appears.

  1. Field Monitoring Protocol. Mini-Split Heat Pumps

    Energy Technology Data Exchange (ETDEWEB)

    Christensen, Dane [National Renewable Energy Lab. (NREL), Golden, CO (United States); Fang, Xia [National Renewable Energy Lab. (NREL), Golden, CO (United States); Tomerlin, Jeff [National Renewable Energy Lab. (NREL), Golden, CO (United States); Winkler, Jon [National Renewable Energy Lab. (NREL), Golden, CO (United States); Hancock, E. [Mountain Energy Partnership, Longmont, CO (United States)

    2011-03-01

    This Building America program report provides a detailed method for accurately measuring and monitoring performance of a residential mini-split heat pump, which will be used in high-performance retrofit applications.

  2. Design of mechanically-tunable photonic crystal split-beam nanocavity.

    Science.gov (United States)

    Lin, Tong; Tian, Feng; Shi, Peng; Chau, Fook Siong; Zhou, Guangya; Tang, Xiaosong; Deng, Jie

    2015-08-01

    Photonic crystal split-beam nanocavities allow for ultra-sensitive optomechanical transductions but are degraded due to their relatively low optical quality factors. We have proposed and experimentally demonstrated a new type of one-dimensional photonic crystal split-beam nanocavity optimized for an ultra-high optical-quality factor. The design is based on the combination of the deterministic method and hill-climbing algorithm. The latter is the simplest and most straightforward method of the local search algorithm that provides the local maximum of the chosen quality factors. This split-beam nanocavity is made up of two mechanical uncoupled cantilever beams with Bragg mirrors patterned onto it and separated by a 75-nm air gap. Experimental results emphasize that the quality factor of the second-order TE mode can be as high as 1.99×10(4). Additionally, one beam of the device is actuated in the lateral direction with the aid of a NEMS actuator, and the quality factor maintains quite well even if there is a lateral offset up to 64 nm. Potentially promising applications, such as sensitive optomechanical torque sensor, local tuning of Fano resonance, all-optical-reconfigurable filters, etc., are foreseen.

  3. Tuning beam power-splitting characteristics through modulating a photonic crystal slab’s output surface

    Science.gov (United States)

    Feng, Shuai; Xiao, Ting-Hui; Gan, Lin; Wang, Yi-Quan

    2017-01-01

    Light-beam-splitting characteristics are theoretically and experimentally studied in 2D square-lattice photonic crystals (PhCs) with delicately designed and modulated output surfaces. Compared with the traditional branch-waveguide and self-collimation-type PhC splitters, our proposed structure can not only split the input light beam into different numbers of branches but also realize the adjustment of their relative light intensities in each branch. Moreover, the influence of a light beam’s incident angle on both the output branch beams’ relative intensity and propagation direction is investigated. This proposed light beam splitter is able to work within a broad frequency range, and the propagation directions of the output split beams can be modified with the incident beam’s frequency. In addition, when the PhC device becomes thicker, a kind of light-beam-focusing phenomenon is observed. Advantageously, our light-beam-splitting device has no restriction as to the incident light beam’s location and width, so it is much more convenient and practical for achieving optical connection with other functional devices in complicated, large-scale, all-optical integrated circuits.

  4. Crystal fields and conduction electrons in praseodymium

    DEFF Research Database (Denmark)

    Clausen, K.N.; Aagaard Sørensen, S.; McEwen, K.A.

    1995-01-01

    The interactions between the crystal-field excitations, the phonons and the conduction electrons in Pr have been studied further. The low-energy satellites to the crystal-field excitations, which are believed to be associated with propagating paramagnon modes in the conduction-electron gas, appear...

  5. Crystal fields of porphyrins and phthalocyanines

    Science.gov (United States)

    Johnson, P. S.; Boukahil, I.; Himpsel, F. J.; Kennedy, C.; Jersett, N.; Cook, P. L.; Garcia-Lastra, J. M.

    2014-03-01

    Polarization-dependent X-ray absorption spectroscopy at the N 1s and metal 2p edges is combined with density functional and atomic multiplet calculations to determine the crystal field parameters 10Dq, Ds, and Dt of transition metal (Mn, Fe, Co, Ni) phthalocyanines and octaethylporphyrins. Octaethyl porphyrins are observed to lie flat on Si with native oxide, while phthalocyanines lie on edge. Strong polarization dependence is found at all edges, which facilitates a unique determination of the crystal field parameters. Crystal field values from PBE density functional calculations provide helpful starting values, which are refined by fitting atomic multiplet calculations to the data. Since the crystal field affects electron-hole separation in solar cells, the systematic set of crystal field parameters obtained here can be useful for optimizing dyes for solar cells.

  6. Influence of exchange splitting on optical properties in gadolinium and dysprosium single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Knyazev, Yu.V.; Bolotin, G.A. (AN SSSR, Sverdlovsk. Inst. Fiziki Metallov)

    1984-12-01

    The temperature dependences of optical conductivity in gadolinium and dysprosium single crystals at the light wave vector polarization along a hexagonal axis and in the basis plane are considered. A substantial anisotropy of interzonal absorption has been found. The sample transition into magnetically ordered state is shown to be accompanied by the emergence of resonance absorption peaks in the near infrared spectral region. The manifestation of these peculiarities is associated with quantum electron transitions between the s-, d-f- interaction-split energy bands near the Fermi level. Main peculiarities of the experimental spectrum of gadolinium optical conductivity found their reflection in theoretically calculated dispersion dependence.

  7. Split green fluorescent protein as a modular binding partner for protein crystallization.

    Science.gov (United States)

    Nguyen, Hau B; Hung, Li-Wei; Yeates, Todd O; Terwilliger, Thomas C; Waldo, Geoffrey S

    2013-12-01

    A modular strategy for protein crystallization using split green fluorescent protein (GFP) as a crystallization partner is demonstrated. Insertion of a hairpin containing GFP β-strands 10 and 11 into a surface loop of a target protein provides two chain crossings between the target and the reconstituted GFP compared with the single connection afforded by terminal GFP fusions. This strategy was tested by inserting this hairpin into a loop of another fluorescent protein, sfCherry. The crystal structure of the sfCherry-GFP(10-11) hairpin in complex with GFP(1-9) was determined at a resolution of 2.6 Å. Analysis of the complex shows that the reconstituted GFP is attached to the target protein (sfCherry) in a structurally ordered way. This work opens the way to rapidly creating crystallization variants by reconstituting a target protein bearing the GFP(10-11) hairpin with a variety of GFP(1-9) mutants engineered for favorable crystallization.

  8. Field Monitoring Protocol: Mini-Split Heat Pumps

    Energy Technology Data Exchange (ETDEWEB)

    Christensen, D.; Fang, X.; Tomerlin, J.; Winkler, J.; Hancock, E.

    2011-03-01

    The report provides a detailed method for accurately measuring and monitoring performance of a residential Mini-Split Heat Pump. It will be used in high-performance retrofit applications, and as part of DOE's Building America residential research program.

  9. Coulomb crystals in the magnetic field

    CERN Document Server

    Baiko, D A

    2009-01-01

    The body-centered cubic Coulomb crystal of ions in the presence of a uniform magnetic field is studied using the rigid electron background approximation. The phonon mode spectra are calculated for a wide range of magnetic field strengths and for several orientations of the field in the crystal. The phonon spectra are used to calculate the phonon contribution to the crystal energy, entropy, specific heat, Debye-Waller factor of ions, and the rms ion displacements from the lattice nodes for a broad range of densities, temperatures, chemical compositions, and magnetic fields. Strong magnetic field dramatically alters the properties of quantum crystals. The phonon specific heat increases by many orders of magnitude. The ion displacements from their equilibrium positions become strongly anisotropic. The results can be relevant for dusty plasmas, ion plasmas in Penning traps, and especially for the crust of magnetars (neutron stars with superstrong magnetic fields $B \\gtrsim 10^{14}$ G). The effect of the magnetic ...

  10. Analysis of guided-resonance-based polarization beam splitting in photonic crystal slabs.

    Science.gov (United States)

    Kilic, Onur; Fan, Shanhui; Solgaard, Olav

    2008-11-01

    We present an analysis of the phase and amplitude responses of guided resonances in a photonic crystal slab. Through this analysis, we obtain the general rules and conditions under which a photonic crystal slab can be employed as a general elliptical polarization beam splitter, separating an incoming beam equally into its two orthogonal constituents, so that half the power is reflected in one polarization state, and half the power is transmitted in the other state. We show that at normal incidence a photonic crystal slab acts as a dual quarter-wave retarder in which the fast and slow axes are switched for reflection and transmission. We also analyze the case where such a structure operates at oblique incidences. As a result we show that the effective dielectric constant of the photonic crystal slab imposes the Brewster angle as a boundary, separating two ranges of angles with different mechanisms of polarization beam splitting. We show that the diattenuation can be tuned from zero to one to make the structure a circular or linear polarization beam splitter. We verify our analytical analysis through finite-difference time-domain simulations and experimental measurements at infrared wavelengths.

  11. Infrared-active excitations related to the R^3+ ligand-field splitting in RMn2O5 (R=Ho, Dy, Tb)

    Science.gov (United States)

    Sirenko, A. A.; O'Malley, S. M.; Kang, T. D.; Kahn, K. H.; Carr, C. L.; Mihaly, L.; Park, S.; Cheong, S.-W.

    2009-03-01

    Optical transitions between ligand-field split states of R^3+ ions in RMn2O5 multiferroic single crystals have been studied at the phase transitions in the external magnetic field up to 13 T and uniaxial pressure up to 5 kbar. Spectra of the ligand field excitations change significantly in external magnetic field and correlate with the reversal of electric polarization induced by magnetic field. The oscillator strength and selection rules for ligand field excitations change with external uniaxial pressure. We discuss the connection between the ligand field on R^3+ with the magnetism and dielectric properties of this compounds.

  12. Power splitting of 1 × 16 in multicore photonic crystal fibers

    Science.gov (United States)

    Malka, Dror; Peled, Aaron

    2017-09-01

    A novel concept of 1 × 16 power splitter based on a variable multicore photonic crystal fiber (PCF) structure is described. Numerical simulations showed how the optical signal can be split in a PCF structure having dimensions of 60 μm × 60 μm × 3.582 mm. The coupled mode analysis and beam propagation method (BPM) was used for analyzing the multicore PCF based 1 × 16 splitter. The input optical signal at a wavelength of 1.55 μm inserted into the central core was divided into sixteen output cores, each with a 6.25% of the total power. The full width half maximum (FWHM) bandwidth found for each core was 100 nm.

  13. Synthesis of single-crystal-like nanoporous carbon membranes and their application in overall water splitting

    KAUST Repository

    Wang, Hong

    2017-01-04

    Nanoporous graphitic carbon membranes with defined chemical composition and pore architecture are novel nanomaterials that are actively pursued. Compared with easy-to-make porous carbon powders that dominate the porous carbon research and applications in energy generation/conversion and environmental remediation, porous carbon membranes are synthetically more challenging though rather appealing from an application perspective due to their structural integrity, interconnectivity and purity. Here we report a simple bottom–up approach to fabricate large-size, freestanding and porous carbon membranes that feature an unusual single-crystal-like graphitic order and hierarchical pore architecture plus favourable nitrogen doping. When loaded with cobalt nanoparticles, such carbon membranes serve as high-performance carbon-based non-noble metal electrocatalyst for overall water splitting.

  14. Crystal Fields in Er0.2Y0.98 Studied by Neutron Scattering

    DEFF Research Database (Denmark)

    Rathmann, Ole; Als-Nielsen, Jens Aage; Bak, Poul Erik;

    1974-01-01

    The splitting of the J=15/2 multiplet of Er in an hcp crystal field has been determined by inelastic neutron scattering from a single crystal of Er0.02Y0.98. Least-squares fits to the spectra gave crystal-field parameters B20=-0.34±0.04, B40=(0.7±0.2)×10-3, B60=(0.21±0.02)×10-4, and B66=(-0.30±0....

  15. Theory of electrolyte crystallization in magnetic field

    DEFF Research Database (Denmark)

    Madsen, Hans Erik Lundager

    2007-01-01

    Crystallization from aqueous solution of a sparingly soluble electrolyte is accelerated by magnetic field if the crystalizing phase is a diamagnetic salt of a weak acid, and crystallization is from neutral or acid solution in ordinary (not heavy) water. Since the effect of Lorentz force...... is negligible, if not absent, the key property is likely to be the spin of protons which, by virtue of their half-integral spin, are fermions. An effect on crystal growth kinetics has been demonstrated, and the apparent effect on nucleation concerns the growth rate of nuclei. We are thus dealing with surface...... phenomena. The basis of the theory is a crystal model of a sparingly soluble salt with NaCl structure, where the ions are divalent, and the anion is a base. It is assumed that almost all the anions in the surface layer are protonized, and that an approaching metal ion pushes the proton away...

  16. Growth, structure, spectral properties and crystal-field analysis of monoclinic Nd:YNbO4 single crystal

    Science.gov (United States)

    Ding, Shoujun; Zhang, Qingli; Gao, Jinyun; Liu, Wenpeng; Luo, Jianqiao; Sun, Dunlu; Sun, Guihua; Wang, Xiaofei

    2016-12-01

    A Nd:YNbO4 single crystal was successfully grown by Czochralski (Cz) method, its structural and spectroscopic properties were investigated. The X-ray rocking curve of the (010) diffraction face of Nd:YNbO4 crystal was measured, the full width at half maximum (FWHM) of this diffraction peak is 0.05°, which indicates a high crystalline quality of the as-grown crystal. Its lattice parameters, atomic coordinates and so on were obtained by Rietvield refinement to X-ray diffraction data. According to the Archimedes drainage method, the crystal density of Nd:YNbO4 is calculated to be 5.4 g/cm3. The Mohr‧s hardness value along (010) face was determined to be 6.0. The transmission spectrum along (010) face at room temperature was recorded and the excitation and emission spectra at 8 K were measured. Photoluminescence peaks of Nd:YNbO4 were assigned, and the crystal-field splitting of Nd3+ in YNbO4 was obtained. The fluorescence lifetime of the 4F3/2→4I11/2 transition of Nd3+ in YNbO4 is fitted to be 152 μs These spectroscopic and energy splitting data give an important reference for the research of laser property of Nd:YNbO4 crystal.

  17. Growth, structure, spectral properties and crystal-field analysis of monoclinic Nd:YNbO{sub 4} single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Shoujun [Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Key Laboratory of Photonic Devices and Materials, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Zhang, Qingli, E-mail: zql@aiofm.ac.cn [Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Key Laboratory of Photonic Devices and Materials, Hefei 230031 (China); Gao, Jinyun; Liu, Wenpeng; Luo, Jianqiao; Sun, Dunlu; Sun, Guihua; Wang, Xiaofei [Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Key Laboratory of Photonic Devices and Materials, Hefei 230031 (China)

    2016-12-15

    A Nd:YNbO{sub 4} single crystal was successfully grown by Czochralski (Cz) method, its structural and spectroscopic properties were investigated. The X-ray rocking curve of the (010) diffraction face of Nd:YNbO{sub 4} crystal was measured, the full width at half maximum (FWHM) of this diffraction peak is 0.05°, which indicates a high crystalline quality of the as-grown crystal. Its lattice parameters, atomic coordinates and so on were obtained by Rietvield refinement to X-ray diffraction data. According to the Archimedes drainage method, the crystal density of Nd:YNbO{sub 4} is calculated to be 5.4 g/cm{sup 3}. The Mohr′s hardness value along (010) face was determined to be 6.0. The transmission spectrum along (010) face at room temperature was recorded and the excitation and emission spectra at 8 K were measured. Photoluminescence peaks of Nd:YNbO{sub 4} were assigned, and the crystal-field splitting of Nd{sup 3+} in YNbO{sub 4} was obtained. The fluorescence lifetime of the {sup 4}F{sub 3/2}→{sup 4}I{sub 11/2} transition of Nd{sup 3+} in YNbO{sub 4} is fitted to be 152 μs These spectroscopic and energy splitting data give an important reference for the research of laser property of Nd:YNbO{sub 4} crystal.

  18. Site-specific herbicide splitting in field carrots based on camera detected weed infestation

    Directory of Open Access Journals (Sweden)

    Dammer, Karl-Heinz

    2014-02-01

    Full Text Available The production of carrots for the German market comes mainly from domestic production. To ensure the efficiency of chemical weed control and to minimize the damage of the crop a splitting of the recommended dosage up to three times is often practiced. Because of large field areas of the carrot cropping and processing enterprises, the potential to save herbicides by practicing an herbicide application adapted to the weed occurrence is high. The efficiency of a site-specific herbicide splitting on the late weed occurrence as well as on yield parameters was tested in field strip trials. Weed species and abundance were determined manually by raster sampling using a counting frame in spring before spraying. Afterwards in the three leaf growth stages of the carrots the weed coverage level was detected online using a camera sensor developed by the Leibniz Institute for Agricultural Engineering (ATB. Based on weed coverage level maps three application zones (200 L ha-1, 300 L ha-1, 400 L ha-1 were defined. On both sides of the site specific splitting strip a uniform splitting strip (400 L ha-1 was applied. The position of the application zones were the same during site-specific splitting at the second and third herbicide spraying respectively. Compared to a conventional uniform splitting herbicide savings were 16% (2005 und 20% (2006 at each spraying time. To evaluate the efficacy of the site-specific splitting on the yield manually harvesting were performed at opposite points in both treatments. The yield parameters fresh weight and numbers of carrots “total” and “marketable” were determined. Assuming a significance level of α = 5% the difference method for controlled treatment comparison in large scale field trials (t-test resulted in 19 of the 24 tests in total no differences between the treatments. The late weed occurrence in both treatments was low.

  19. View of the Split-Field Magnet facility

    CERN Multimedia

    1975-01-01

    Also shown the spectrometer of experiment R413 installed on the right at 90 deg to the intersecting beams and the movable chambers and hodoscopes of experiment R410 installed on the opposite side of the Spli-Field Magnet (see Annual Report 1975)

  20. Validation of SplitVectors Encoding for Quantitative Visualization of Large-Magnitude-Range Vector Fields.

    Science.gov (United States)

    Henan Zhao; Bryant, Garnett W; Griffin, Wesley; Terrill, Judith E; Jian Chen

    2017-06-01

    We designed and evaluated SplitVectors, a new vector field display approach to help scientists perform new discrimination tasks on large-magnitude-range scientific data shown in three-dimensional (3D) visualization environments. SplitVectors uses scientific notation to display vector magnitude, thus improving legibility. We present an empirical study comparing the SplitVectors approach with three other approaches - direct linear representation, logarithmic, and text display commonly used in scientific visualizations. Twenty participants performed three domain analysis tasks: reading numerical values (a discrimination task), finding the ratio between values (a discrimination task), and finding the larger of two vectors (a pattern detection task). Participants used both mono and stereo conditions. Our results suggest the following: (1) SplitVectors improve accuracy by about 10 times compared to linear mapping and by four times to logarithmic in discrimination tasks; (2) SplitVectors have no significant differences from the textual display approach, but reduce cluttering in the scene; (3) SplitVectors and textual display are less sensitive to data scale than linear and logarithmic approaches; (4) using logarithmic can be problematic as participants' confidence was as high as directly reading from the textual display, but their accuracy was poor; and (5) Stereoscopy improved performance, especially in more challenging discrimination tasks.

  1. Splitting full matrix algebras over algebraic number fields

    CERN Document Server

    Ivanyos, Gábor; Schicho, Joseph

    2011-01-01

    Let K be an algebraic number field of degree d and discriminant D over Q. Let A be an associative algebra over K given by structure constants such that A is siomorphic to the algebra M_n(K) of n by n matrices over K for some positive integer n. Suppose that d, n and D are bounded. Then an isomorphism of A with M_n(K) can be constructed by a polynomial time ff-algorithm. (An ff-algorithm is a deterministic procedure which is allowed to call oracles for factoring integers and factoring univariate polynomials over finite fields.) As a consequence, we obtain a polynomial time ff-algorithm to compute isomorphisms of central simple algebras of bounded degree over K.

  2. Potential fields of merging and splitting filaments in air

    Institute of Scientific and Technical Information of China (English)

    Ma Yuan-Yuan; Lu Xin; Xi Ting-Ting; Hao Zuo-Qiang; Gong Qi-Huang; Zhang Jie

    2007-01-01

    Two interacting light filaments with different initial phases propagating in air are investigated numerically by using a ray tracing method. The evolution of the rays of a filament is governed by a potential field. During propagation, the two potential wells of the two filaments can merge into one or repel each other, depending on the initial phase difference between the two filaments. The study provides a simple description of the interacting filaments.

  3. Wide-Field OCT Angiography at 400 KHz Utilizing Spectral Splitting

    Directory of Open Access Journals (Sweden)

    Laurin Ginner

    2014-10-01

    Full Text Available Optical angiography systems based on optical coherence tomography (OCT require dense sampling in order to maintain good vascular contrast. We demonstrate a way to gain acquisition speed and spatial sampling by using spectral splitting with a swept source OCT system. This method splits the recorded spectra into two to several subspectra. Using continuous lateral scanning, the lateral sampling is then increased by the same factor. This allows increasing the field of view of OCT angiography, while keeping the same transverse resolution and measurement time. The performance of our method is demonstrated in vivo at different locations of the human retina and verified quantitatively. Spectral splitting can be applied without any changes in the optical setup, thus offering an easy way to increase the field of view of OCT in general and in particular for OCT angiography.

  4. High Field Magnetization of Tb Single Crystals

    DEFF Research Database (Denmark)

    Roeland, L. W.; Cock, G. J.; Lindgård, Per-Anker

    1975-01-01

    The magnetization of Tb single crystals was measured in magnetic fields to 34T along the hard direction at temperature of 1.8, 4.2, 65.5 and 77K, and along with easy direction at 4.2 and 77K. The data are compared with the results of a self-consistent spin wave calculation using a phenomenological...

  5. Simulation of multi-frequency EPR spectra for a distribution of the zero-field splitting

    Science.gov (United States)

    Azarkh, Mykhailo; Groenen, Edgar J. J.

    2015-06-01

    We present a numerical procedure called 'grid-of-errors' to extract the distribution of magnetic interactions from continuous-wave electron-paramagnetic-resonance (EPR) spectra at multiple microwave frequencies. The approach is based on the analysis of the lineshape of the spectra and explicitly worked out for high-spin systems for which the lineshape is determined by a distribution of the zero-field splitting. Initial principal values of the zero-field splitting tensor are obtained from the EPR spectrum at a microwave frequency in the high-field limit, and the initial distribution is taken Gaussian. Subsequently, the grid-of-errors procedure optimizes this distribution, without any restriction to its shape, taking into account spectra at various microwave frequencies. The numerical procedure is illustrated for the Fe(III)-EDTA complex. An optimized distribution of the zero-field splitting is obtained, which provides a proper description of the EPR spectra at 9.5, 34, 94, and 275 GHz. The proposed approach can be used as well for distributions of magnetic interactions other than the zero-field splitting.

  6. Exchange field effect in the crystal field ground state of CeMAl{sub 4}Si{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Kai; Strigari, Fabio; Sundermann, Martin; Severing, Andrea [University of Cologne, Cologne (Germany); Agrestini, Stefano [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Bauer, Eric D.; Sarrao, John L.; Thompson, Joe D. [Los Alamos National Laboratory, Los Alamos, NM (United States); Otero, Edwige [Synchrotron Soleil, Gif-sur-Yvette (France); Tanaka, Arata [Hiroshima University, Higashi-Hiroshima (Japan)

    2016-07-01

    The crystal-field ground state wave functions of the tetragonal Kondo lattice materials CeMAl{sub 4}Si{sub 2}(M = Rh, Ir and Pt), as well as the crystal-field splittings, are determined with low temperature linear polarized soft x-ray absorption spectroscopy. Surprisingly, at T < 20 K, which is far below the first excited crystal-field level at 200 K, a change in linear dichroism was observed that cannot be accounted for by population of crystal-field states. Adding an exchange field to the ionic full multiplet calculations below 20 K leads to a splitting to the ground state doublet and modification of J{sub z} admixture, thus accounting for the change in low temperature linear dichroism. The direction of the required exchange field is parallel along c-axis for the antiferromagnetic Rh and Ir compounds, and perpendicular to c-axis for ferromagnetic CePtAl{sub 4}Si{sub 2}.

  7. Zero Field Splitting of the chalcogen diatomics using relativistic correlated wave-function methods

    DEFF Research Database (Denmark)

    Rota, Jean-Baptiste; Knecht, Stefan; Fleig, Timo;

    2011-01-01

    ) methods are used as well as two-step methods Spin-Orbit Complete Active Space Perturbation Theory at 2nd order (SO-CASPT2) and Spin-Orbit Difference Dedicated Configuration Interaction (SODDCI). The energy of the X21 state corresponds to the Zero-Field Splitting (ZFS) of the ground state spin triplet...

  8. Crystal field in ErGa sub 3 - a neutron spectroscopy study

    CERN Document Server

    Murasik, A; Clementyev, E; Schefer, J

    2000-01-01

    The splitting of the J=15/2 multiplet of Er sup 3 sup + in a cubic crystal field has been determined by inelastic scattering from a polycrystalline sample of ErGa sub 3. On the basis of the observed intensities and their temperature variation we have been able to determine two crystal electric field (CEF) parameters required for cubic symmetry. Least-squares fits applied to the observed spectra taken at various temperatures gave crystal field parameters: B sub 4 =(7.15+-0.05)x10 sup - sup 5 and B sub 6 =(1.28+-0.05)x10 sup - sup 6 meV yielding the GAMMA sub 7 doublet as a ground level with the overall splitting of 10.92 meV. The results are used to calculate the temperature-dependant zero-field magnetisation, the Schottky anomaly of the specific heat associated with the CEF splitting of Er sup 3 sup + in ErGa sub 3 , and the high-field magnetisation.

  9. Paramagnetic NMR chemical shift in a spin state subject to zero-field splitting

    CERN Document Server

    Soncini, Alessandro

    2012-01-01

    We derive a general formula for the paramagnetic NMR nuclear shielding tensor of an open-shell molecule in a pure spin state, subject to a zero-field splitting (ZFS). Our findings are in contradiction with a previous proposal. We present a simple application of the newly derived formula to the case of a triplet ground state split by an easy-plane ZFS spin Hamiltonian. When $kT$ is much smaller than the ZFS gap, thus a single non-degenerate level is thermally populated, our approach correctly predicts a temperature-independent paramagnetic shift, while the previous theory leads to a Curie temperature dependence.

  10. Mean-field models for disordered crystals

    CERN Document Server

    Cancès, Eric; Lewin, Mathieu

    2012-01-01

    In this article, we set up a functional setting for mean-field electronic structure models of Hartree-Fock or Kohn-Sham types for disordered crystals. The electrons are quantum particles and the nuclei are classical point-like articles whose positions and charges are random. We prove the existence of a minimizer of the energy per unit volume and the uniqueness of the ground state density of such disordered crystals, for the reduced Hartree-Fock model (rHF). We consider both (short-range) Yukawa and (long-range) Coulomb interactions. In the former case, we prove in addition that the rHF ground state density matrix satisfies a self-consistent equation, and that our model for disordered crystals is the thermodynamic limit of the supercell model.

  11. Crystal field and magnetism with Wannier functions:rare-earth doped aluminum garnets

    Institute of Scientific and Technical Information of China (English)

    Eva Mihóková; Pavel Novák; Valentin V. Laguta

    2015-01-01

    Using the recently developed method we calculated the crystal field parameters in yttrium and lutetium aluminum garnets doped with seven trivalent Kramers rare-earth ions. We then inserted calculated parameters into the atomic-like Hamiltonian taking into account the electron-electron, spin-orbit and Zeeman interactions and determined the multiplet splitting by the crystal field as well as magneticĝ tensors. We compared calculated results with available experimental data. Very good agreement with the spectro-scopic data and qualitative agreement with experimentalĝ tensors was found.

  12. Guiding, bending, and splitting of coupled defect surface modes in a surface-wave photonic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Zhen; Gao, Fei [Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore 637371 (Singapore); Zhang, Baile, E-mail: blzhang@ntu.edu.sg [Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore 637371 (Singapore); Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore, Singapore 637371 (Singapore)

    2016-01-25

    We experimentally demonstrate a type of waveguiding mechanism for coupled surface-wave defect modes in a surface-wave photonic crystal. Unlike conventional spoof surface plasmon waveguides, waveguiding of coupled surface-wave defect modes is achieved through weak coupling between tightly localized defect cavities in an otherwise gapped surface-wave photonic crystal, as a classical wave analogue of tight-binding electronic wavefunctions in solid state lattices. Wave patterns associated with the high transmission of coupled defect surface modes are directly mapped with a near-field microwave scanning probe for various structures including a straight waveguide, a sharp corner, and a T-shaped splitter. These results may find use in the design of integrated surface-wave devices with suppressed crosstalk.

  13. Analysis of oxygen shell splitting in hydrothermally grown single crystal ThO{sub 2}(200)

    Energy Technology Data Exchange (ETDEWEB)

    Kelly, T.D.; Petrosky, J.C.; McClory, J.W. [Department of Engineering Physics, Air Force Institute of Technology, 2950 Hobson Way, WPAFB, OH 45433 (United States); Mann, J.M. [Air Force Research Laboratory, Sensors Directorate, Wright-Patterson AFB, OH 45433 (United States); Kolis, J.W. [Department of Chemistry and Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson University, Clemson, SC 29634-0973 (United States)

    2015-11-15

    Single crystals of ThO{sub 2} have been synthesized using hydrothermal growth and studied using the X-ray absorption fine structure (XAFS) technique. The extended X-ray absorption fine structure (EXAFS) has been extracted from the XAFS and analyzed using a novel, computational Latin hypercube sampling method. The methodology not only confirms the expected space group and crystal structure, it also identifies the origin of a previously reported split O shell. Since EXAFS is a local order analysis technique, the O shell splitting is identified as an O atom occupying an interstitial site. This result is significant for examining O{sup 2-} transport in a ThO{sub 2} matrix and corroborating research indicating partial Th 5f occupancy that is similar to hyper-stoichiometric UO{sub 2+x} compounds. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Monitoring dyke injection and strain field evolution using shear-wave splitting.

    Science.gov (United States)

    Kendall, J.-M.; Verdon, J. P.; Keir, D.; Baird, A.

    2012-04-01

    Magma storage and dyke injection in the shallow crust is a fundamental process in rifting and volcanic environments. The dyking will tend to align with directions of maximum compressive stress, and the associated aligned fracturing and melt migration provides a very effective means of generating seismic anisotropy. Observations of shear-wave splitting provide one of the most unambiguous indicators of such anisotropy. As such, shear-wave splitting can be used to monitor the evolving strain field in volcanic and rifting environments. Here we apply lessons learned from monitoring fracture propagation during the hydraulic stimulation of tight-gas reservoirs. In a number of experiments we observe spatial and temporal variations in shear-wave splitting magnitude and orientation. We invert shear-wave observations for fracture properties, including the tangential and normal compliance, the ratio of which is a good indicator of fluid flow and permeability. Frequency dependent affects can be also used to indicate the length scales of the causative cracks or fractures. We apply these insights to microseismic data recently acquired across the volcanically active Afar triple junction in Ethiopia. The pattern of S-wave splitting in Afar is best explained by anisotropy from deformation-related structures, with the dramatic change in splitting parameters into the rift axis from the increased density of dyke-induced faulting combined with a contribution from oriented melt pockets near volcanic centres. The results help in our understanding of the role of melt in strain accommodation in rifting and volcanic environments.

  15. Synthesis of passive lossless metasurfaces using auxiliary fields for reflectionless beam splitting and perfect reflection

    CERN Document Server

    Epstein, Ariel

    2016-01-01

    We introduce a paradigm for accurate design of metasurfaces for intricate beam manipulation, implementing functionalities previously considered impossible to achieve with passive lossless elements. The key concept involves self-generation of auxiliary evanescent fields which facilitate the required local power conservation, without interfering with the device performance in the far field. We demonstrate our scheme by presenting exact reactive solutions to the challenging problems of reflectionless beam splitting and perfect reflection, verified via full wave simulations.

  16. Synthesis of Passive Lossless Metasurfaces Using Auxiliary Fields for Reflectionless Beam Splitting and Perfect Reflection.

    Science.gov (United States)

    Epstein, Ariel; Eleftheriades, George V

    2016-12-16

    We introduce a paradigm for accurate design of metasurfaces for intricate beam manipulation, implementing functionalities previously considered impossible to achieve with passive lossless elements. The key concept involves self-generation of auxiliary evanescent fields which facilitate the required local power conservation, without interfering with the device performance in the far field. We demonstrate our scheme by presenting exact reactive solutions to the challenging problems of reflectionless beam splitting and perfect reflection, verified via full wave simulations.

  17. Ions confined in spherical dielectric cavities modeled by a splitting field-theory

    Energy Technology Data Exchange (ETDEWEB)

    Lue, Leo, E-mail: leo.lue@strath.ac.uk [Department of Chemical and Process Engineering, University of Strathclyde, James Weir Building, 75 Montrose Street, Glasgow G1 1XJ (United Kingdom); Linse, Per [Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, S-221 00 Lund (Sweden)

    2015-04-14

    The properties of ions confined within spherical dielectric cavities are examined by a splitting field-theory and Monte Carlo simulations. Three types of cavities are considered: one possessing a uniform surface charge density, one with a uniform volume charge density, and one containing mobile ions. In all cases, mobile counterions are present within the dielectric sphere. The splitting theory is based on dividing the electrostatic interaction into long- and short-wavelength contributions and applying different approximations on the two contributions. The splitting theory works well for the case where the dielectric constant of the confining sphere is equal to or less than that of the medium external to the sphere. Nevertheless, by extending the theory with a virial expansion, the predictions are improved. However, when the dielectric constant of the confining sphere is greater than that of the medium outside the sphere, the splitting theory performs poorly, only qualitatively agreeing with the simulation data. In this case, the strong-coupling expansion does not seem to work well, and a modified mean-field theory where the counterions interact directly with only their own image charge gives improved predictions. The splitting theory works best for the system with a uniform surface charge density and worst for the system with a uniform volume charge density. Increasing the number of ions within the sphere, at a fixed radius, tends to increase the ion density near the surface of the sphere and leads to a depletion region in the sphere interior; however, varying the ion number does not lead to any qualitative changes in the performance of the splitting theory.

  18. Eighth-order phase-field-crystal model for two-dimensional crystallization

    OpenAIRE

    Jaatinen, A.; Ala-Nissila, T.

    2010-01-01

    We present a derivation of the recently proposed eighth order phase field crystal model [Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase field crystal models. We find that among the phase field crystal models...

  19. Spin-orbit qubits of rare-earth-metal ions in axially symmetric crystal fields.

    Science.gov (United States)

    Bertaina, S; Shim, J H; Gambarelli, S; Malkin, B Z; Barbara, B

    2009-11-27

    Contrary to the well-known spin qubits, rare-earth-metal qubits are characterized by a strong influence of crystal field due to large spin-orbit coupling. At low temperature and in the presence of resonance microwaves, it is the magnetic moment of the crystal-field ground state which nutates (for several micros) and the Rabi frequency Omega(R) is anisotropic. Here, we present a study of the variations of Omega(R)(H(0)) with the magnitude and direction of the static magnetic field H(0) for the odd 167Er isotope in a single crystal CaWO(4):Er(3+). The hyperfine interactions split the Omega(R)(H(0)) curve into eight different curves which are fitted numerically and described analytically. These "spin-orbit qubits" should allow detailed studies of decoherence mechanisms which become relevant at high temperature and open new ways for qubit addressing using properly oriented magnetic fields.

  20. Enhanced trapped field performance of bulk high-temperature superconductors using split coil, pulsed field magnetization with an iron yoke

    Science.gov (United States)

    Ainslie, M. D.; Fujishiro, H.; Mochizuki, H.; Takahashi, K.; Shi, Y.-H.; Namburi, D. K.; Zou, J.; Zhou, D.; Dennis, A. R.; Cardwell, D. A.

    2016-07-01

    Investigating and predicting the magnetization of bulk superconducting materials and developing practical magnetizing techniques is crucial to using them as trapped field magnets in engineering applications. The pulsed field magnetization (PFM) technique is considered to be a compact, mobile and relative inexpensive way to magnetize bulk samples, requiring shorter magnetization times (on the order of milliseconds) and a smaller and less complicated magnetization fixture; however, the trapped field produced by PFM is generally much smaller than that of slower zero field cooling or field cooling techniques, particularly at lower operating temperatures. In this paper, the PFM of two, standard Ag-containing Gd-Ba-Cu-O samples is carried out using two types of magnetizing coils: (1) a solenoid coil, and (2) a split coil, both of which make use of an iron yoke to enhance the trapped magnetic field. It is shown that a significantly higher trapped field can be achieved using a split coil with an iron yoke, and in order to explain these how this arrangement works in detail, numerical simulations using a 2D axisymmetric finite element method based on the H -formulation are carried to qualitatively reproduce and analyze the magnetization process from both electromagnetic and thermal points of view. It is observed that after the pulse peak significantly less flux exits the bulk when the iron core is present, resulting in a higher peak trapped field, as well as more overall trapped flux, after the magnetization process is complete. The results have important implications for practical applications of bulk superconductors as such a split coil arrangement with an iron yoke could be incorporated into the design of a portable, high magnetic field source/magnet to enhance the available magnetic field or in an axial gap-type bulk superconducting electric machine, where iron can be incorporated into the stator windings to (1) improve the trapped field from the magnetization process

  1. Unexpected effect of substituents on the zero-field splitting of triplet phenyl nitrenes

    Science.gov (United States)

    Korchagin, Denis V.; Akimov, Alexander V.; Yureva, Elena A.; Aldoshin, Sergei M.; Misochko, Eugenii Ya.

    2016-08-01

    The EPR spectrum of triplet 2,4,6-tribromophenyl nitrene was obtained in glassy methylcyclohexane at 15 K. Surprisingly, the zero-field splitting parameter D = 0.989 cm-1 derived from this spectrum is much lower than that reported previously for triplet 3,5-diazido-2,4,6-tribromophenyl nitrene and has the same value as in phenyl nitrenes composed with light atoms. DFT calculations of the zero-field splitting parameters support this unexpected experimental observation. Experimental and theoretical data provide evidence that the enhanced by bromine atoms spin-orbit contribution to the parameter D (the so called ;heavy-atom effect;) is strongly modulated by other substituents attached to the aromatic cycle.

  2. Photon splitting in a strong magnetic field recalculation and comparison with previous calculations

    CERN Document Server

    Adler, Stephen Louis; Adler, Stephen L; Schubert, Christian

    1996-01-01

    We recalculate the amplitude for photon splitting in a strong magnetic field below the pair production threshold, using the worldline path integral variant of the Bern--Kosower formalism. Numerical comparison (using programs that we have made available for public access on the Internet) shows that the results of the recalculation are identical to the earlier calculations of Adler and later of Stoneham, and to the recent recalculation by Baier, Milstein, and Shaisultanov.

  3. The effect of spin polarization on zero field splitting parameters in paramagnetic pi-electron molecules.

    Science.gov (United States)

    van Gastel, Maurice

    2009-09-28

    Spin polarization effects play an important role in the theory of isotropic hyperfine interactions for aromatic protons. The spin polarization gives rise to significant isotropic proton hyperfine interactions--spin-dependent one-electron properties--smaller than 0 MHz and the effect has been theoretically described [H. M. McConnell and D. B. J. Chesnut, Chem. Phys. 28, 107 (1958)]. The influence of spin polarization on the zero field splitting parameters, which are spin-dependent two-electron properties, has not been clearly identified yet. A phenomenological equation is proposed here for the contribution of spin polarization to the zero field splitting parameter D in analogy to McConnell's equation for hyperfine interactions. The presence of the effect is demonstrated in a series of calculations on polyacenes in the triplet state and turns out to be responsible for up to 50% of the D parameter in the case of naphthalene! It is found that spin-unrestricted single-determinant methods, including the widely used density functional theory methods, do not accurately reproduce the two-electron reduced electron density required for the evaluation of two-electron spin-dependent properties. For the accurate calculation of zero field splitting parameters by quantum chemical methods, it thus seems necessary to resort to correlated ab initio methods which do not give rise to spin contamination and which do provide an accurate description of the two-electron reduced electron density.

  4. Pitchfork Bifurcation and Zharov Splitting in Nonlinear Mid-infrared Photothermal Spectroscopy in a liquid crystal using a Quantum Cascade Laser

    CERN Document Server

    Mertiri, Alket; Hong, M K; Mehta, P; Mertz, J; Ziegler, L D; Erramilli, Shyamsunder

    2013-01-01

    We report on the mid-infrared nonlinear photothermal spectrum of the neat liquid crystal 4-Octyl-4'-Cyanobiphenyl (8CB) using a tunable Quantum Cascade Laser (QCL). The nonequilibrium steady state characterized by the nonlinear photothermal infrared response undergoes a supercritical pitchfork bifurcation. The bifurcation, observed in heterodyne two-color pump-probe detection, leads to ultrasharp nonlinear infrared spectra similar to those reported in the visible region. A systematic study of the peak splitting as function of absorbed infrared power shows the bifurcation has a critical exponent of 0.5. The surprising observation of an apparently universal critical exponent in a nonequilibrium state is explained using a simple model reminiscent of mean field theory. Apart from the intrinsic interest for nonequilibrium studies, nonlinear photothermal methods lead to a dramatic narrowing of spectral lines, giving rise to a potential new contrast mechanism for the rapidly emerging new field of mid-infrared micros...

  5. Temperature fields in a growing solar silicon crystal

    Directory of Open Access Journals (Sweden)

    Kondrik A. I.

    2012-06-01

    Full Text Available The optimal thermal terms for growing by Czochralski method Si single-crystals, suitable for making photoelectric energy converters, has been defined by the computer simulation method. Dependences of temperature fields character and crystallization front form on the diameter of the crystal, stage and speed of growing, and also on correlation between diameter and height of the crystal has been studied.

  6. The Level-split of the Two-level Entangled Atom in an Optical Field

    Institute of Scientific and Technical Information of China (English)

    CAO Zhuoliang; HUANG Ting; GUO Guangcan; YI Youming

    2002-01-01

    The behavior of a two-level entangled atom in an optical field with circular polarization is studied in this paper. The interaction of an optical field and one of the entangled atoms is analyzed in detail. A general solution of the SchrAo¨Gdinger equation about the motion of the entangled atom is obtained. The properties of the action are dependent on the initial state of the atom. By detecting the entangled atom out of the field, we can obtain the state of the other atom moving in the field. It is shown that the state of the atom out of the field will influence the energies of the split-levels of the atom in the field.

  7. Anisotropic magnetic properties and crystal electric field studies on CePd2Ge2 single crystal.

    Science.gov (United States)

    Maurya, Arvind; Kulkarni, R; Dhar, S K; Thamizhavel, A

    2013-10-30

    The anisotropic magnetic properties of the antiferromagnetic compound CePd2Ge2, crystallizing in the tetragonal crystal structure have been investigated in detail on a single crystal grown by the Czochralski method. From the electrical transport, magnetization and heat capacity data, the Néel temperature is confirmed to be 5.1 K. Anisotropic behaviour of the magnetization and resistivity is observed along the two principal crystallographic directions-namely, [100] and [001]. The isothermal magnetization measured in the magnetically ordered state at 2 K exhibits a spin reorientation at 13.5 T for the field applied along the [100] direction, whereas the magnetization is linear along the [001] direction attaining a value of 0.94 μ(B)/Ce at 14 T. The reduced value of the magnetization is attributed to the crystalline electric field (CEF) effects. A sharp jump in the specific heat at the magnetic ordering temperature is observed. After subtracting the phononic contribution, the jump in the heat capacity amounts to 12.5 J K(-1)mol(-1) which is the expected value for a spin ½ system. From the CEF analysis of the magnetization data the excited crystal field split energy levels were estimated to be at 120 K and 230 K respectively, which quantitatively explains the observed Schottky anomaly in the heat capacity. A magnetic phase diagram has been constructed based on the field dependence of magnetic susceptibility and the heat capacity data.

  8. Oxidation and crystal field effects in uranium

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, J. G. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Booth, C. H. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Shuh, D. K. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); van der Laan, G. [Diamond Light Source, Didcot (United Kingdom); Sokaras, D. [Stanford Synchrotron Radiation Lightsource, Stanford, CA (United States); Weng, T. -C. [Stanford Synchrotron Radiation Lightsource, Stanford, CA (United States); Yu, S. W. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Bagus, P. S. [Univ. of North Texas, Denton, TX (United States); Tyliszczak, T. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Nordlund, D. [Stanford Synchrotron Radiation Lightsource, Stanford, CA (United States)

    2015-07-06

    An extensive investigation of oxidation in uranium has been pursued. This includes the utilization of soft x-ray absorption spectroscopy, hard x-ray absorption near-edge structure, resonant (hard) x-ray emission spectroscopy, cluster calculations, and a branching ratio analysis founded on atomic theory. The samples utilized were uranium dioxide (UO2), uranium trioxide (UO3), and uranium tetrafluoride (UF4). As a result, a discussion of the role of non-spherical perturbations, i.e., crystal or ligand field effects, will be presented.

  9. Vibrational dynamics of zero-field-splitting hamiltonian in gadolinium-based MRI contrast agents from ab initio molecular dynamics.

    Science.gov (United States)

    Lasoroski, Aurélie; Vuilleumier, Rodolphe; Pollet, Rodolphe

    2014-07-07

    The electronic relaxation of gadolinium complexes used as MRI contrast agents was studied theoretically by following the short time evolution of zero-field-splitting parameters. The statistical analysis of ab initio molecular dynamics trajectories provided a clear separation between static and transient contributions to the zero-field-splitting. For the latter, the correlation time was estimated at approximately 0.1 ps. The influence of the ligand was also probed by replacing one pendant arm of our reference macrocyclic complex by a bulkier phosphonate arm. In contrast to the transient contribution, the static zero-field-splitting was significantly influenced by this substitution.

  10. Magnetic Field in Superlattices Semiconductors of Crystals

    Directory of Open Access Journals (Sweden)

    Luciano Nascimento

    2015-05-01

    Full Text Available In this work we present a study on the super-semiconductor networks, using the Kronig-Penney model for the effective mass approximation, and then the calculations for the application of the magnetic field perpendicular and parallel to the layers of super lattices crystals. The magnetic field applied parallel to the layers, was used to adjust the resonance of a higher energy subband of a well by thermal excitation with a lower energy subband of the adjacent well, increasing energy levels in its tunneling rate. We use the formalism of Schrödinger equation of quantum mechanics. Introducing the calculations in a systematic way in superlattices for each semiconductor quantum well to assess their energy spectrum systematically studied.

  11. Measuring 10-20 T magnetic fields in single wire explosions using Zeeman splitting.

    Science.gov (United States)

    Banasek, J T; Engelbrecht, J T; Pikuz, S A; Shelkovenko, T A; Hammer, D A

    2016-10-01

    We have shown that the Zeeman splitting of the sodium (Na) D-lines at 5890 Å and 5896 Å can be used to measure the magnetic field produced by the current flowing in an exploding wire prior to wire explosion. After wire explosion, the lines in question are either not visible in the strong continuum from the exploding wire plasma, or too broad to measure the magnetic field by methods discussed in this paper. We have determined magnetic fields in the range 10-20 T, which lies between the small field and Paschen-Back regimes for the Na D-lines, over a period of about 70 ns on a 10 kA peak current machine. The Na source is evaporated drops of water with a 0.171 M NaCl solution deposited on the wire. The Na desorbs from the wire as it heats up, and the excited vapor atoms are seen in emission lines. The measured magnetic field, determined by the Zeeman splitting of these emission lines, estimates the average radial location of the emitting Na vapor as a function of time under the assumption the current flows only in the wire during the time of the measurement.

  12. Measuring 10-20 T magnetic fields in single wire explosions using Zeeman splitting

    Science.gov (United States)

    Banasek, J. T.; Engelbrecht, J. T.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.

    2016-10-01

    We have shown that the Zeeman splitting of the sodium (Na) D-lines at 5890 Å and 5896 Å can be used to measure the magnetic field produced by the current flowing in an exploding wire prior to wire explosion. After wire explosion, the lines in question are either not visible in the strong continuum from the exploding wire plasma, or too broad to measure the magnetic field by methods discussed in this paper. We have determined magnetic fields in the range 10-20 T, which lies between the small field and Paschen-Back regimes for the Na D-lines, over a period of about 70 ns on a 10 kA peak current machine. The Na source is evaporated drops of water with a 0.171 M NaCl solution deposited on the wire. The Na desorbs from the wire as it heats up, and the excited vapor atoms are seen in emission lines. The measured magnetic field, determined by the Zeeman splitting of these emission lines, estimates the average radial location of the emitting Na vapor as a function of time under the assumption the current flows only in the wire during the time of the measurement.

  13. Photonic crystal and quasi-crystals providing simultaneous light coupling and beam splitting within a low refractive-index slab waveguide.

    Science.gov (United States)

    Shi, Jingxing; Pollard, Michael E; Angeles, Cesar A; Chen, Ruiqi; Gates, J C; Charlton, M D B

    2017-05-12

    Coupling between free space components and slab waveguides is a common requirement for integrated optical devices, and is typically achieved by end-fire or grating coupling. Power splitting and distribution requires additional components. Usually grating couplers are used in combination with MMI/Y-splitters to do this task. In this paper, we present a photonic crystal device which performs both tasks simultaneously and is able to couple light at normal incidence and near normal incidence. Our approach is scalable to large channel counts with little impact on device footprint. We demonstrate in normal incidence coupling with multi-channel splitting for 785 nm light. Photonic crystals are etched into single mode low refractive index SiON film on both SiO2/Si and borosilicate glass substrate. Triangular lattices are shown to provide coupling to 6 beams with equal included angle (60°), while a quasi-crystal lattice with 12-fold rotational symmetry yields coupling to 12 beams with equal included angle (30°). We show how to optimize the lattice constant to achieve efficient phase matching between incident and coupled mode wave vectors, and how to adjust operating wavelength from visible to infrared wavelengths.

  14. Three-dimensional dose accumulation in pseudo-split-field IMRT and brachytherapy for locally advanced cervical cancer

    DEFF Research Database (Denmark)

    Sun, Baozhou; Yang, Deshan; Esthappan, Jackie

    2015-01-01

    intensity-modulated radiation therapy (IMRT) and image-guided BT in locally advanced cervical cancer. METHODS AND MATERIALS: Thirty-three patients treated with split-field-IMRT to 45.0-51.2 Gy in 1.6-1.8 Gy per fraction to the elective pelvic lymph nodes and to 20 Gy to the central pelvis region were......PURPOSE: Dose accumulation of split-field external beam radiotherapy (EBRT) and brachytherapy (BT) is challenging because of significant EBRT and BT dose gradients in the central pelvic region. We developed a method to determine biologically effective dose parameters for combined split-field...... to be -1 ± 4 Gy, -3 ± 5 Gy, 2 ± 3 Gy, and -3 ± 5 Gy for bladder, rectum, sigmoid, and GTV, respectively. CONCLUSIONS: It is feasible to perform 3D EQD2 dose accumulation to assess high and intermediate dose regions for combined split-field IMRT and BT....

  15. Birefringence-induced splitting of the Zero-dispersion wavelength in nonlinear photonic crystal fibers

    DEFF Research Database (Denmark)

    Hansen, Kim Per; Petersson, A.; Folkenberg, Jakob Riis

    2004-01-01

    for transverse structural uniformity by adopting a simple effective-index approach in which the birefringence is calculated in a step-index fiber with an elliptical core. We find that to reduce the splitting to less than 1nm the birefringence should be less than 210 -5 , resulting in a transverse uniformity...

  16. Generation of surface-wave microwave microplasmas in hollow-core photonic crystal fiber based on a split-ring resonator.

    Science.gov (United States)

    Vial, Florian; Gadonna, Katell; Debord, Benoît; Delahaye, Frédéric; Amrani, Foued; Leroy, Olivier; Gérôme, Frédéric; Benabid, Fetah

    2016-05-15

    We report on a new and highly compact scheme for the generation and sustainment of microwave-driven plasmas inside the core of an inhibited coupling Kagome hollow-core photonic crystal fiber. The microwave plasma generator consists of a split-ring resonator that efficiently couples the microwave field into the gas-filled fiber. This coupling induces the concomitant generation of a microwave surface wave at the fiber core surround and a stable plasma column confined in the fiber core. The scheme allowed the generation of several centimeters long argon microplasma columns with a very low excitation power threshold. This result represents an important step toward highly compact plasma lasers or plasma-based photonic components.

  17. Constraining the Solar Coronal Magnetic Field Strength using Split-band Type II Radio Burst Observations

    Science.gov (United States)

    Kishore, P.; Ramesh, R.; Hariharan, K.; Kathiravan, C.; Gopalswamy, N.

    2016-11-01

    We report on low-frequency radio (85-35 MHz) spectral observations of four different type II radio bursts, which exhibited fundamental-harmonic emission and split-band structure. Each of the bursts was found to be closely associated with a whitelight coronal mass ejection (CME) close to the Sun. We estimated the coronal magnetic field strength from the split-band characteristics of the bursts, by assuming a model for the coronal electron density distribution. The choice of the model was constrained, based on the following criteria: (1) when the radio burst is observed simultaneously in the upper and lower bands of the fundamental component, the location of the plasma level corresponding to the frequency of the burst in the lower band should be consistent with the deprojected location of the leading edge (LE) of the associated CME; (2) the drift speed of the type II bursts derived from such a model should agree closely with the deprojected speed of the LE of the corresponding CMEs. With the above conditions, we find that: (1) the estimated field strengths are unique to each type II burst, and (2) the radial variation of the field strength in the different events indicate a pattern. It is steepest for the case where the heliocentric distance range over which the associated burst is observed is closest to the Sun, and vice versa.

  18. Sub-natural $N$-type Resonance in Cesium Atomic Vapor: splitting in magnetic fields

    CERN Document Server

    Slavov, D; Sarkisyan, D; Mirzoyan, R; Krasteva, A; Wilson-Gordon, A D; Cartaleva, S

    2013-01-01

    The sub-natural-width $N$-type resonance in {\\Lambda}-system, on the $D_2$ line of Cs atoms is studied for the first time in the presence of a buffer gas (neon) and the radiations of two continuous narrow band diode lasers. $L$ = 1 cm long cell is used to investigate $N$-type process. The $N$-type resonance in a magnetic field for $^{133}$Cs atoms is shown to split into seven or eight components, depending on the magnetic field and laser radiation directions. The results obtained indicate that levels $F_g$ = 3, 4 are initial and final in the N resonance formation. The experimental results with magnetic field agree well with the theoretical curves.

  19. Eighth-order phase-field-crystal model for two-dimensional crystallization

    OpenAIRE

    Jaatinen, A.; Ala-Nissilä, Tapio

    2010-01-01

    We present a derivation of the recently proposed eighth-order phase-field crystal model [A. Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two-dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase-field crystal models. We find that among the phase-field crystal mod...

  20. Study of Events with Identified Forward Particles at the Split Field Magnet

    CERN Multimedia

    2002-01-01

    This experiment will study two aspects of particle production in the forward region : \\item 1) In the recent discovery of charm production in hadronic interactions at the Split Field Magnet, the triggering on strange particles at medium p^t has proven to be a very effective tool for the study of heavy resonances, especially those carrying new flavours like charm and beauty. We want to carry out a more detailed investigation of the production-dynamics of charmed particles, together with a search for beauty mesons and baryons. \\item 2) A trigger on forward particles at high p^t ($>$ 5GeV/c) provides unique features to determine the properties of the parton-parton subprocesses. We want to study the relative contributions of quark, diquark and gluon scattering.\\\\ \\\\ This experimental programme will be carried out, using the improved Split Field Magnet spectrometer (SFM). The different detection systems provide : \\item a) Detection and momentum analysis of charged particles in 4@p solid angle. An improved programm...

  1. On the Stickelberger splitting map in the $K$--theory of number fields

    CERN Document Server

    Banaszak, Grzegorz

    2010-01-01

    The Stickelberger splitting map in the case of abelian extensions $F / \\Q$ was defined in [Ba1, Chap. IV]. The construction used Stickelebrger's theorem. For abelian extensions $F / K$ with an arbitrary totally real base field $K$ the construction of \\cite{Ba1} cannot be generalized since Brumer's conjecture (the analogue of Stickelberger's theorem) is not proved yet at that level of generality. In this paper, we construct a general Stickelberger splitting map under the assumption that the first Stickelberger elements annihilate the Quillen $K$--groups groups $K_2 ({\\mathcal O}_{F_{l^k}})$ for the Iwasawa tower $F_{l^k} := F(\\mu_{l^k})$, for $k \\geq 1.$ The results of [Po] give examples of CM abelian extensions $F/K$ of general totally real base-fields $K$ for which the first Stickelberger elements annihilate $K_2 ({\\mathcal O}_{F_{l^k}})_l$ for all $k \\geq 1$, while this is proved in full generality in [GP], under the assumption that the Iwasawa $\\mu$--invariant $\\mu_{F,l}$ vanishes. As a consequence, our St...

  2. Guiding, bending, and splitting of coupled defect surface modes in a surface-wave photonic crystal

    CERN Document Server

    Gao, Zhen; Zhang, Baile

    2016-01-01

    We experimentally demonstrate a type of waveguiding mechanism for coupled surface-wave defect modes in a surface-wave photonic crystal. Unlike conventional spoof surface plasmon waveguides, waveguiding of coupled surface-wave defect modes is achieved through weak coupling between tightly localized defect cavities in an otherwise gapped surface-wave photonic crystal, as a classical wave analogue of tight-binding electronic wavefunctions in solid state lattices.

  3. Magnetism and crystal field in TmCu sub 2

    Energy Technology Data Exchange (ETDEWEB)

    Sima, V.; Smetana, Z.; Divis, M.; Svoboda, P.; Zajac, S. (Karlova Univ., Prague (CS)); Bischof, J.; (Vyzkummy Ustav Silmoproude Elektrotechniky, Bechovice (CS)); Lebech, B. (Risoe National Lab., Roskilde (DK)); Kayzel, F. (Amsterdam Univ. (NL). Natuurkundig Lab.)

    1988-12-01

    The crystal field energies and Gruneisen parameters of the individual crystal field levels of Tm{sup 3+} in TmCu{sub 2} were determined from specific heat and thermal expansion data above T{sub N}. The magnetic phase transitions are discussed with respect to magnetic entropy and molar volume.

  4. Virtual Breakdown Mechanism: Field-Driven Splitting of Pure Water for Hydrogen Production

    CERN Document Server

    Wang, Yifei; Wu, Wei

    2016-01-01

    Due to the low conductivity of pure water, using an electrolyte is common for achieving efficient water electrolysis. In this paper, we have broken through this common sense by using deep-sub-Debye-length nanogap electrochemical cells for the electrolysis of pure water. At such nanometer scale, the field-driven pure water splitting exhibits a completely different mechanism from the macrosystem. We have named this process 'virtual breakdown mechanism' that results in a series of fundamental changes and more than 10^5-fold enhancement of the equivalent conductivity of pure water. This fundamental discovery has been theoretically discussed in this paper and experimentally demonstrated in a group of electrochemical cells with nanogaps between two electrodes down to 37 nm. Based on our nanogap electrochemical cells, the electrolysis current from pure water is comparable to or even larger than the current from 1 mol/L sodium hydroxide solution, indicating the high-efficiency of pure water splitting as a potential f...

  5. Steering far-field spin-dependent splitting of light by inhomogeneous anisotropic media

    CERN Document Server

    Ling, Xiaohui; Luo, Hailu; Wen, Shuangchun

    2012-01-01

    An inhomogeneous anisotropic medium with specific structure geometry can apply tunable spin-dependent geometrical phase to the light passing through the medium, and thus can be used to steer the spin-dependent splitting (SDS) of light. In this paper, we exemplify this inference by the $q$-plate, an inhomogeneous anisotropic medium. It is demonstrated that when a linearly polarized light beam normally passes through a $q$-plate, $k$-space SDS first occurs, and then the real-space SDS in the far-field focal plane of a converging lens is distinguishable. Interestingly, the SDS, described by the normalized Stokes parameter $S_3$, shows a multi-lobe and rotatable splitting pattern with rotational symmetry. Further, by tailoring the structure geometry of $q$-plate or/and incident polarization angle of light, the lobe number and the rotation angle both are tunable. Our result suggests that the $q$-plate can serve as potential devices for manipulating the photon spin states and enable applications such as in nano-opt...

  6. Mounting an ISR intersection chamber in the Split Field Magnet(SFM)

    CERN Multimedia

    1977-01-01

    The Split Field Magnet (SFM) was the largest spectrometer for particles from beam-beam collisions in the ISR. It could determine particle momenta in a large solid angle, but was designed mainly for the analysis of forward travelling particles.As the magnet was working on the ISR circulating beams, its magnetic field had to be such as to restore the correct proton orbit.The SFM, therefore, produced zero field at the crossing point and fields of opposite signs upstream and downstream of it and was completed by 2 large and 2 small compensator magnets. The gradient effects were corrected by magnetic channels equipped with movable flaps. The useful magnetic field volume was 28 m3, the induction in the median plane 1.14 T, the gap heigth 1.1 m, the length 10.5 m, the weight about 1000 ton.Concerning the detectors, the SFM was the first massive application of multiwire proportional chambers (about 70000 wires) which filled the main and the large compensator magnets. In the course of the years different types of vacu...

  7. Discrete electric field mediated droplet splitting in microchannels: Fission, Cascade, and Rayleigh modes.

    Science.gov (United States)

    Chaudhuri, Joydip; Timung, Seim; Dandamudi, Chola Bhargava; Mandal, Tapas Kumar; Bandyopadhyay, Dipankar

    2017-01-01

    Numerical simulations supplemented by experiments together uncovered that strategic integration of discrete electric fields in a non-invasive manner could substantially miniaturize the droplets into smaller parts in a pressure driven oil-water flow inside microchannels. The Maxwell's stress generated from the electric field at the oil-water interface could deform, stretch, neck, pin, and disintegrate a droplet into many miniaturized daughter droplets, which eventually ushered a one-step method to form water-in-oil microemulsion employing microchannels. The interplay between electrostatic, inertial, capillary, and viscous forces led to various pathways of droplet breaking, namely, fission, cascade, or Rayleigh modes. While a localized electric field in the fission mode could split a droplet into a number of daughter droplets of smaller size, the cascade or the Rayleigh mode led to the formation of an array of miniaturized droplets when multiple electrodes generating different field intensities were ingeniously assembled around the microchannel. The droplets size and frequency could be tuned by varying the field intensity, channel diameter, electrode locations, interfacial tension, and flow ratio. The proposed methodology shows a simple methodology to transform a microdroplet into an array of miniaturized ones inside a straight microchannel for enhanced mass, energy, and momentum transfer, and higher throughput. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Time-domain electric field enhancement on micrometer scale in coupled split ring resonator upon terahertz radiation

    DEFF Research Database (Denmark)

    Lange, Simon Lehnskov; Iwaszczuk, Krzysztof; Hoffmann, Matthias

    2016-01-01

    We present here a novel design for a coupled split ring resonator antenna optimized for time-domain electric field enhancement in the 0.1 to 1 terahertz (THz) range. The antenna is designed to be sensitive to the incident field polarization and seeks to avoid metal damage due to electron bombardm...

  9. Time-domain electric field enhancement on micrometer scale in coupled split ring resonator upon terahertz radiation

    DEFF Research Database (Denmark)

    Lange, Simon Lehnskov; Iwaszczuk, Krzysztof; Hoffmann, Matthias;

    2016-01-01

    We present here a novel design for a coupled split ring resonator antenna optimized for time-domain electric field enhancement in the 0.1 to 1 terahertz (THz) range. The antenna is designed to be sensitive to the incident field polarization and seeks to avoid metal damage due to electron...

  10. Effect of a step quantum well structure and an electric-field on the Rashba spin splitting

    Institute of Scientific and Technical Information of China (English)

    Hao Yafei; Chen Yonghai; Hao Guodong; Wang Zhanguo

    2009-01-01

    Spin splitting of conduction subbands in Al0.3Ga0.7As/GaAs/AlxGa1-xAs/Al0.3Gaa7As step quantum wells induced by interface and electric field related Rashba effects is investigated theoretically by the method of finite difference. The dependence of the spin splitting on the electric field and the well structure, which is controlled by the well width and the step width, is investigated in detail. Without an external electric field, the spin splitting is induced by an in terface related Rashba term due to the built-in structure inversion asymmetry. Applying the external electric field to the step QW, the Rashba effect can be enhanced or weakened, depending on the well structure as well as the direction and the magnitude of the electric field. The spin splitting is mainly controlled by the interface related Rashba term under a negative and a stronger positive electric field, and the contribution of the electric field related Rashba term dominates in a small range of a weaker positive electric field. A method to determine the interface parameter is proposed. The results show that the step QWs might be used as spin switches.

  11. Zero-Magnetic-Field Spin Splitting of Polaron's Ground State Energy Induced by Rashba Spin-Orbit Interaction

    Institute of Scientific and Technical Information of China (English)

    LIU Jia; XIAO Jing-Ling

    2006-01-01

    We study theoretically the ground state energy of a polaron near the interface of a polar-polar semiconductor by considering the Rashba spin-orbit (SO) coupling with the Lee-Low-Pines intermediate coupling method. Our numerical results show that the Rashba SO interaction originating from the inversion asymmetry in the heterostructure splits the ground state energy of the polaron. The electron arealdensity and vector dependence of the ratio of the SO interaction to the total ground state energy or other energy composition are obvious. One can see that even without any external magnetic field, the ground state energy can be split by the Rashba SO interaction, and this split is not a single but a complex one. Since the presents of the phonons, whose energy gives negative contribution to the polaron's,the spin-splitting states of the polaron are more stable than electron's.

  12. Study of ln s Physics in $\\bar{p}p$ Interactions at the Split Field Magnet

    CERN Multimedia

    2002-01-01

    This experiment uses the Split Field Magnet detector to investigate the low p^t, ``ln~s'', type of interactions that dominate the @*p cross-section. Systematic comparisons will be made to pp interactions. \\\\ \\\\ Specific areas to be studied include elastic scattering in the regions 0.05 $<$ !t! $<$ 0.8 GeV|2 and 0.8 $<$ !t! $<$ 4.0 GeV|2, and the use of a minimum bias trigger to study topological cross-sections, inclusive spectra, and two-body correlations. Some specialized triggers, run simultaneously with the high t elastic scattering trigger, are being studied. Examples are a trigger requiring Cerenkov identification in a limited region of phase space, and a trigger to select diffractively produced events.

  13. Acoustic beam splitting in two-dimensional phononic crystals using self-collimation effect

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jing [Department of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006 (China); Department of Experiment Education, Guangdong University of Technology, Guangzhou 510006 (China); Wu, Fugen, E-mail: wufugen@21cn.com; Zhong, Huilin [Department of Experiment Education, Guangdong University of Technology, Guangzhou 510006 (China); Yao, Yuanwei; Zhang, Xin [Department of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006 (China)

    2015-10-14

    We propose two models of self-collimation-based beam splitters in phononic crystals. The finite element method is used to investigate the propagation properties of acoustic waves in two-dimensional phononic crystals. The calculated results show that the efficiency of the beam splitter can be controlled systematically by varying the radius of the rods or by changing the orientation of the square rods in the line defect. The effect of changing the side length of the square rods on acoustic wave propagation is discussed. The results show that the total transmission/reflection range decreases/increases as the side length increases. We also find that the relationship between the orientation of the transflective point and the side length of the square rods is quasi-linear.

  14. Effects of magnetic fields on dissolution of arthritis causing crystals

    Science.gov (United States)

    Takeuchi, Y.; Iwasaka, M.

    2015-05-01

    The number of gout patients has rapidly increased because of excess alcohol and salt intake. The agent responsible for gout is the monosodium urate (MSU) crystal. MSU crystals are found in blood and consist of uric acid and sodium. As a substitute for drug dosing or excessive water intake, physical stimulation by magnetic fields represents a new medical treatment for gout. In this study, we investigated the effects of a magnetic field on the dissolution of a MSU crystal suspension. The white MSU crystal suspension was dissolved in an alkaline solution. We measured the light transmission of the MSU crystal suspension by a transmitted light measuring system. The magnetic field was generated by a horizontal electromagnet (maximum field strength was 500 mT). The MSU crystal suspension that dissolved during the application of a magnetic field of 500 mT clearly had a higher dissolution rate when compared with the control sample. We postulate that the alkali solution promoted penetration upon diamagnetic rotation and this magnetic field orienting is because of the pronounced diamagnetic susceptibility anisotropy of the MSU crystal. The results indicate that magnetic fields represent an effective gout treatment approach.

  15. Low-temperature magnetic susceptibility and zero-field splitting in some high-spin manganese(III) compounds

    Energy Technology Data Exchange (ETDEWEB)

    Cofield, M.L.; Bryan, P.S.

    1986-02-03

    We have determined the value of the ground-state zero-field splitting parameter D for several high-spin d/sup 4/ Mn(III) compounds from average susceptibility measurements down to 5 K with a SQUID magnetometer. The zero-field splittings in these compounds are similar to some results reported for Mn(III) porphyrins and are insensitive to ligand structure and axial halide binding, in contrast to what has been reported for the analogous Fe(III) compounds. (orig./HBR).

  16. Pressure-Induced Shifts of R, R', and B Line-Groups and Ground-State Zero-Field-Splitting of Ruby

    Institute of Scientific and Technical Information of China (English)

    MA Dong-Ping; CHEN Ju-Rong

    2005-01-01

    By means of improved ligand-field theory, the "pure electronic" presure-induced shifts (PS's) and the PS's due to electron-phonon interaction (EPI) of the R1, R2, B1, B2, B3, and R'3 lines and the ground-state zero-field-splitting of ruby have been uniformly calculated. The calculation results are in very good agreement with all the experimental data. At normal pressure, ruby is a crystal with very strong crystal field. Thus, the admixture of |t22 (3T1)e4T2> and |t3 2 2 E> bases in the wavefunction of R1 level of ruby is small at normal pressure, and it gradually decreases with increasing pressure, which causes the R1-line PS of ruby to monotonously red shift with approximate linearity. The combined effect of the pure electronic PS of R1 line and the PS of R1 line due to EPI gives rise to the total PS of R1 line. The analyses and comparisons among the features of R1-line PS's of three laser crystals (ruby, GSGG:Cr3+ and GGG:Cr3+ ) have been made, and the origin of their difference has been revealed.

  17. Enhancement of crystal homogeneity of protein crystals under application of an external alternating current electric field

    Energy Technology Data Exchange (ETDEWEB)

    Koizumi, H.; Uda, S.; Fujiwara, K.; Nozawa, J. [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577 (Japan); Tachibana, M. [Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027 (Japan); Kojima, K. [Department of Education, Yokohama Soei University, 1 Miho-tyou, Midori-ku, Yokohama, 226-0015 (Japan)

    2014-10-06

    X-ray diffraction rocking-curve measurements were performed on tetragonal hen egg white (HEW) lysozyme crystals grown with and without the application of an external alternating current (AC) electric field. The crystal quality was assessed by the full width at half maximum (FWHM) value for each rocking curve. For two-dimensional maps of the FWHMs measured on the 440 and the 12 12 0 reflection, the crystal homogeneity was improved under application of an external electric field at 1 MHz, compared with that without. In particular, the significant improvement of the crystal homogeneity was observed for the 12 12 0 reflection.

  18. Effect of magnetic field on the crystallization of zinc sulfate

    Directory of Open Access Journals (Sweden)

    Freitas A. M. B.

    2000-01-01

    Full Text Available The effect of magnetic field on the crystallization of diamagnetic zinc sulfate was investigated in a series of controlled batch cooling experiments. Zinc sulfate solutions were exposed to magnetic fields of different intensities, up to a maximum of 0.7T. A clear influence of magnetic field on the following zinc sulfate crystallization parameters was found: an increase in saturation temperature, a decrease in metastable zone width, and an increase in growth rate and average crystal size. These effects were observed for the diamagnetic zinc sulfate, but not in similar, previously reported experiments for paramagnetic copper sulfate.

  19. Crystal-Field Engineering of Solid-State Laser Materials

    Science.gov (United States)

    Henderson, Brian; Bartram, Ralph H.

    2005-08-01

    This book examines the underlying science and design of laser materials. It emphasizes the principles of crystal-field engineering and discusses the basic physical concepts that determine laser gain and nonlinear frequency conversion in optical crystals. Henderson and Bartram develop the predictive capabilities of crystal-field engineering to show how modification of the symmetry and composition of optical centers can improve laser performance. They also discuss applications of the principles of crystal-field engineering to a variety of optical crystals in relation to the performances of laser devices. This book will be of considerable interest to physical, chemical and material scientists and to engineers involved in the science and technology of solid state lasers.

  20. Beam splitting at the output of photonic crystal waveguides with discrete surface point defects.

    Science.gov (United States)

    Wang, Qi; Zhang, Lanlan; Li, Qi

    2010-11-08

    With the method of adding two point defects on modulated surface, novel photonic crystal (PC) waveguide-based beam splitters were presented. The modulated surface layer supports surface states, and introduced discrete point defects can serve as discrete light emitters. The finite-difference time-domain (FDTD) simulations show that the number of beams is sensitive to the distance of two point defects. By adjusting the positions of the point defects, 1-to-N beam splitters can be realized. These simple, easy-to-fabricate and controllable structures have important potential applications in integrated optical circuits.

  1. Paired modes of heterostructure cavities in photonic crystal waveguides with split band edges

    DEFF Research Database (Denmark)

    Mahmoodian, Sahand; Sukhorukov, Andrey A.; Ha, Sangwoo

    2010-01-01

    We investigate the modes of double heterostructure cavities where the underlying photonic crystal waveguide has been dispersion engineered to have two band-edges inside the Brillouin zone. By deriving and using a perturbative method, we show that these structures possess two modes. For unapodized...... cavities, the relative detuning of the two modes can be controlled by changing the cavity length, and for particular lengths, a resonant-like effect makes the modes degenerate. For apodized cavities no such resonances exist and the modes are always non-degenerate....

  2. Cooling System Design for a Split High Field Bitter-type Electromagnet

    Science.gov (United States)

    Birmingham, William; Bates, Evan; Romero-Talamas, Carlos; Rivera, William

    2014-10-01

    For the purpose of analyzing magnetized dusty plasma at the University of Maryland Baltimore County (UMBC), we are designing a split resistive electromagnet. When completed, the magnet will be capable of generating fields of 10 T for 10 seconds. The type of design proposed here was originally developed by Francis Bitter, and achieves high magnetic fields by helically stacked disk-shaped solenoids with axially oriented cooling channels. In order to ensure the safety and functionality of the apparatus, the geometry and placement of the cooling passages must be designed to establish a manageable temperature profile throughout the coil. The estimated power consumption from resistive losses is nearly 7 MW, thus it is imperative to optimize the cooling capacity of the system. The cooling capacity is limited by the mass of chilled water available at one time and the maximum achievable mass flow through the coils. The system is also designed to withstand the resultant mechanical stresses from the Lorentz force. Slot-shaped cooling channels are used. The number and placement of these channels is optimized through an iterative and integrated design process which combines analytic calculations with finite element analyses. The methodology and results of the design process is presented.

  3. Electron spin relaxation due to reorientation of a permanent zero field splitting tensor.

    Science.gov (United States)

    Schaefle, Nathaniel; Sharp, Robert

    2004-09-15

    Electron spin relaxation of transition metal ions with spin S> or =1 results primarily from thermal modulation of the zero field splitting (zfs) tensor. This occurs both by distortion of the zfs tensor due to intermolecular collisions and, for complexes with less than cubic symmetry, by reorientational modulation of the permanent zfs tensor. The reorientational mechanism is much less well characterized in previous work than the distortional mechanism although it is an important determinant of nuclear magnetic resonance (NMR) paramagnetic relaxation enhancement phenomena (i.e., the enhancement of NMR relaxation rates produced by paramagnetic ions in solution or NMR-PRE). The classical density matrix theory of spin relaxation does not provide an appropriate description of the reorientational mechanism at low Zeeman field strengths because the zero-order spin wave functions are stochastic functions of time. Using spin dynamics simulation techniques, the time correlation functions of the spin operators have been computed and used to determine decay times for the reorientational relaxation mechanism for S=1. In the zfs limit of laboratory field strengths (H(Zeem)spin decay is exponential, the spin relaxation time, tau(S) (composite function) approximately 0.53tau(R)((1)), where tau(R)((1)) is the reorientational correlation time of a molecule-fixed vector. The value of tau(S) (composite function) is independent of the magnitude of the cylindrical zfs parameter (D), but it depends strongly on low symmetry zfs terms (the E/D ratio). Other spin dynamics (SD) simulations examined spin decay in the intermediate regime of field strengths where H(Zeem) approximately H(zfs) (composite function), and in the vicinity of the Zeeman limit. The results demonstrate that the reorientational electron spin relaxation mechanism is often significant when H(zfs) (composite function)> or =H(Zeem), and that its neglect can lead to serious errors in the interpretation of NMR-PRE data.

  4. Eighth-order phase-field-crystal model for two-dimensional crystallization

    Science.gov (United States)

    Jaatinen, A.; Ala-Nissila, T.

    2010-12-01

    We present a derivation of the recently proposed eighth-order phase-field crystal model [A. Jaatinen , Phys. Rev. E 80, 031602 (2009)10.1103/PhysRevE.80.031602] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two-dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase-field crystal models. We find that among the phase-field crystal models studied, the eighth-order fitting scheme gives results in good agreement with the density functional theory for both static and dynamic properties, suggesting it is an accurate and computationally efficient approximation to the density functional theory.

  5. Near-field probing of photonic crystals

    NARCIS (Netherlands)

    Flück, E.; Hammer, M.; Vos, W.L.; Hulst, van N.F.; Kuipers, L.

    2004-01-01

    Photonic crystals form an exciting new class of optical materials that can greatly affect optical propagation and light emission. As the relevant length scale is smaller than the wavelength of light, sub-wavelength detection forms an important ingredient to obtain full insight in the physical proper

  6. Goethite liquid crystals and magnetic field effects

    NARCIS (Netherlands)

    van den Pol, E

    2010-01-01

    In this thesis the liquid crystal phase behavior of colloidal, boardlike, goethite (alpha-FeOOH) particles is described. Apart from the nematic phase, a smectic A phase is formed in systems with a low and high polydispersity. Strong fractionation occurs which is able to reduce the local length polyd

  7. Intermittent dislocation density fluctuations in crystal plasticity from a phase-field crystal model

    DEFF Research Database (Denmark)

    Tarp, Jens M.; Angheluta, Luiza; Mathiesen, Joachim;

    2014-01-01

    Plastic deformation mediated by collective dislocation dynamics is investigated in the two-dimensional phase-field crystal model of sheared single crystals. We find that intermittent fluctuations in the dislocation population number accompany bursts in the plastic strain-rate fluctuations. Disloc...

  8. Terahertz field enhancement via coherent superposition of the pulse sequences after a single optical-rectification crystal

    Science.gov (United States)

    Sajadi, Mohsen; Wolf, Martin; Kampfrath, Tobias

    2014-03-01

    Terahertz electromagnetic pulses are frequently generated by optical rectification of femtosecond laser pulses. In many cases, the efficiency of this process is known to saturate with increasing intensity of the generation beam because of two-photon absorption. Here, we demonstrate two routes to reduce this effect in ZnTe(110) crystals and enhance efficiency, namely, by (i) recycling the generation pulses and by (ii) splitting each generation pulse into two pulses before pumping the crystal. In both methods, the second pulse arrives ˜1 ns after the first one, sufficiently long for optically generated carriers to relax. Enhancement is achieved by coherently superimposing the two resulting terahertz fields.

  9. Terahertz field enhancement via coherent superposition of the pulse sequences after a single optical-rectification crystal

    Energy Technology Data Exchange (ETDEWEB)

    Sajadi, Mohsen, E-mail: sajadi@fhi-berlin.mpg.de; Wolf, Martin; Kampfrath, Tobias [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany)

    2014-03-03

    Terahertz electromagnetic pulses are frequently generated by optical rectification of femtosecond laser pulses. In many cases, the efficiency of this process is known to saturate with increasing intensity of the generation beam because of two-photon absorption. Here, we demonstrate two routes to reduce this effect in ZnTe(110) crystals and enhance efficiency, namely, by (i) recycling the generation pulses and by (ii) splitting each generation pulse into two pulses before pumping the crystal. In both methods, the second pulse arrives ∼1 ns after the first one, sufficiently long for optically generated carriers to relax. Enhancement is achieved by coherently superimposing the two resulting terahertz fields.

  10. Split-step finite-difference time-domain method with perfectly matched layers for efficient analysis of two-dimensional photonic crystals with anisotropic media.

    Science.gov (United States)

    Singh, Gurpreet; Tan, Eng Leong; Chen, Zhi Ning

    2012-02-01

    This Letter presents a split-step (SS) finite-difference time-domain (FDTD) method for the efficient analysis of two-dimensional (2-D) photonic crystals (PhCs) with anisotropic media. The proposed SS FDTD method is formulated with perfectly matched layer boundary conditions and caters for inhomogeneous anisotropic media. Furthermore, the proposed method is derived using the efficient SS1 splitting formulas with simpler right-hand sides that are more efficient and easier to implement. A 2-D PhC cavity with anisotropic media is used as an example to validate the efficiency of the proposed method.

  11. Metal-dielectric composites for beam splitting and far-field deep sub-wavelength resolution for visible wavelengths.

    Science.gov (United States)

    Yan, Changchun; Zhang, Dao Hua; Zhang, Yuan; Li, Dongdong; Fiddy, M A

    2010-07-05

    We report beam splitting in a metamaterial composed of a silver-alumina composite covered by a layer of chromium containing one slit. By simulating distributions of energy flow in the metamaterial for H-polarized waves, we find that the beam splitting occurs when the width of the slit is shorter than the wavelength, which is conducive to making a beam splitter in sub-wavelength photonic devices. We also find that the metamaterial possesses deep sub-wavelength resolution capabilities in the far field when there are two slits and the central silver layer is at least 36 nm in thickness, which has potential applications in superresolution imaging.

  12. Mapping individual electromagnetic field components inside a photonic crystal

    CERN Document Server

    Denis, T; Lee, J H H; van der Slot, P J M; Vos, W L; Boller, K -J

    2012-01-01

    We present a method to map the absolute electromagnetic field strength inside photonic crystals. We apply the method to map the electric field component Ez of a two-dimensional photonic crystal slab at microwave frequencies. The slab is placed between two mirrors to select Bloch standing waves and a subwavelength spherical scatterer is scanned inside the resulting resonator. The resonant Bloch frequencies shift depending on the electric field at the position of the scatterer. To map the electric field component Ez we measure the frequency shift in the reflection and transmission spectrum of the slab versus the scatterer position. Very good agreement is found between measurements and calculations without any adjustable parameters.

  13. Ap stars with resolved magnetically split lines: Magnetic field determinations from Stokes I and V spectra⋆

    Science.gov (United States)

    Mathys, G.

    2017-05-01

    Context. Some Ap stars that have a strong enough magnetic field and a sufficiently low v sini show spectral lines resolved into their magnetically split components. Aims: We present the results of a systematic study of the magnetic fields and other properties of those stars. Methods: This study is based on 271 new measurements of the mean magnetic field modulus ⟨ B ⟩ of 43 stars, 231 determinations of the mean longitudinal magnetic field ⟨ Bz ⟩ and of the crossover ⟨ Xz ⟩ of 34 stars, and 229 determinations of the mean quadratic magnetic field ⟨ Bq ⟩ of 33 stars. Those data were used to derive new values or meaningful lower limits of the rotation periods Prot of 21 stars. Variation curves of the mean field modulus were characterised for 25 stars, the variations of the longitudinal field were characterised for 16 stars, and the variations of the crossover and of the quadratic field were characterised for 8 stars. Our data are complemented by magnetic measurements from the literature for 41 additional stars with magnetically resolved lines. Phase coverage is sufficient to define the curve of variation of ⟨ B ⟩ for 2 of these stars. Published data were also used to characterise the ⟨ Bz ⟩ curves of variation for 10 more stars. Furthermore, we present 1297 radial velocity measurements of the 43 Ap stars in our sample that have magnetically resolved lines. Nine of these stars are spectroscopic binaries for which new orbital elements were derived. Results: The existence of a cut-off at the low end of the distribution of the phase-averaged mean magnetic field moduli ⟨ B ⟩ av of the Ap stars with resolved magnetically split lines, at about 2.8 kG, is confirmed. This reflects the probable existence of a gap in the distribution of the magnetic field strengths in slowly rotating Ap stars, below which there is a separate population of stars with fields weaker than 2 kG. In more than half of the stars with magnetically resolved lines that have a

  14. Field renormalization in photonic crystal waveguides

    DEFF Research Database (Denmark)

    Colman, Pierre

    2015-01-01

    A novel strategy is introduced in order to include variations of the nonlinearity in the nonlinear Schro¨dinger equation. This technique, which relies on renormalization, is in particular well adapted to nanostructured optical systems where the nonlinearity exhibits large variations up to two...... Schro¨dinger equation is an occasion for physics-oriented considerations and unveils the potential of photonic crystal waveguides for the study of new nonlinear propagation phenomena....

  15. Superposition model analysis of nickel(II) ions in trigonal bipyramidal complexes exhibiting huge zero field splitting (aka 'giant magnetic anisotropy')

    Science.gov (United States)

    Rudowicz, Czesław; Açıkgöz, Muhammed; Gnutek, Paweł

    2017-07-01

    Potential single-ion magnet Ni2+ systems: [Ni(Me6tren)Cl](ClO4) and [Ni(Me6tren)Br](Br) reveal unusually high zero field splitting (ZFS). The ZFS parameter (ZFSP) Dexpt = -120 to -180 cm-1 was determined indirectly by high-magnetic field, high-frequency electron magnetic resonance (HMF-EMR). Modeling ZFSPs using the density functional theory (DFT) codes predicts D values: -100 to -200 cm-1. Such ZFSP values may seem controversial in view of the D values usually not exceeding several tens of cm-1 for Ni2+ ions. To corroborate or otherwise these results and elucidate the origin of the huge ZFS (named inappropriately as 'giant uniaxial magnetic anisotropy') and respective wavefunctions, we have undertaken semiempirical modeling based on the crystal field (CF) and spin Hamiltonians (SH) theory. In this paper, a feasibility study is carried out to ascertain if superposition model (SPM) calculations may yield such huge D values for these Ni2+ systems. Using crystal structure data for [Ni(Me6tren)Cl](ClO4) and [Ni(Me6tren)Br](Br) as well as taking into account the Jahn-Teller distortions of five-fold coordinated Ni-complexes revealed by DFT geometry optimization, the ZFSPs are predicted for several structural models and wide ranges of model parameters. The results indicate that in the presence of the Jahn-Teller distortions, the SPM-predicted ZFSP D may achieve the observed magnitudes, whereas the positive as well as negative D-signs are obtainable. Further studies based on SPM calculations of CF parameters and diagonalization of the Hamiltonian (Hfree ion + HCF) will allow considering the wavefunctions compositions and thus actual origin of the splitting between the ground and first excited state.

  16. Field induced heliconical structure of cholesteric liquid crystal

    Science.gov (United States)

    Lavrentovich, Oleg D.; Shiyanovsii, Sergij V.; Xiang, Jie; Kim, Young-Ki

    2017-06-27

    A diffraction grating comprises a liquid crystal (LC) cell configured to apply an electric field through a cholesteric LC material that induces the cholesteric LC material into a heliconical state with an oblique helicoid director. The applied electric field produces diffracted light from the cholesteric LC material within the visible, infrared or ultraviolet. The axis of the heliconical state is in the plane of the liquid crystal cell or perpendicular to the plane, depending on the application. A color tuning device operates with a similar heliconical state liquid crystal material but with the heliconical director axis oriented perpendicular to the plane of the cell. A power generator varies the strength of the applied electric field to adjust the wavelength of light reflected from the cholesteric liquid crystal material within the visible, infrared or ultraviolet.

  17. Nucleation of lysozyme crystals under external electric and ultrasonic fields

    Science.gov (United States)

    Nanev, Christo N.; Penkova, Anita

    2001-11-01

    Preferred orientation along c-axis of hen-egg-white lysozyme (HEWL) crystals has been observed in an external electric field. Besides, the HEWL crystals grew predominantly on the cathode side of the glass cell. These facts were explained on the basis of a concept for specific spatial distribution of the positive electric charges on the individual HEWL molecules, and thus attributed to the (preferred) orientation of individual HEWL molecules in the solution, under these conditions. Ultrasonic field redoubles the nucleation rate of HEWL crystals, but does not change the number of building units in the critical nucleus. Taking into account the intermolecular binding energy, we conclude that ultrasonic field accelerates nucleation due to breaking of the protein crystals.

  18. Fractional-topological-charge-induced vortex birth and splitting of light fields on the submicron scale

    Science.gov (United States)

    Fang, Yiqi; Lu, Qinghong; Wang, Xiaolei; Zhang, Wuhong; Chen, Lixiang

    2017-02-01

    The study of vortex dynamics is of fundamental importance in understanding the structured light's propagation behavior in the realm of singular optics. Here, combining with the large-angle holographic lithography in photoresist, a simple experiment to trace and visualize the vortex birth and splitting of light fields induced by various fractional topological charges is reported. For a topological charge M =1.76 , the recorded microstructures reveal that although it finally leads to the formation of a pair of fork gratings, these two vortices evolve asynchronously. More interestingly, it is observed on the submicron scale that high-order topological charges M =3.48 and 3.52, respectively, give rise to three and four characteristic forks embedded in the samples with one-wavelength resolution of about 450 nm. Numerical simulations based on orbital angular momentum eigenmode decomposition support well the experimental observations. Our method could be applied effectively to study other structured matter waves, such as the electron and neutron beams.

  19. Interaction of polar molecules with resonant radio frequency electric fields: imaging of the NO molecular beam splitting.

    Science.gov (United States)

    Cáceres, J O; Morato, M; González Ureña, A

    2006-12-28

    The interaction between a NO supersonic beam and a resonant radio frequency (RF) field is investigated using laser ionization coupled to imaging techniques. It is shown how the resonant interaction leads to a beam splitting of +/-0.2 degrees toward both positive and negative direction perpendicular to the beam propagation axis. This phenomenon is rationalized using a model based on molecular interferences produced by the action of the resonant RF electric field.

  20. Split-field vs extended-field intensity-modulated radiation therapy plans for oropharyngeal cancer: Which spares the larynx? Which spares the thyroid?

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Yao; Chen, Josephine [Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA (United States); Leary, Celeste I. [Department of Radiation Medicine, Oregon Health Sciences University, Portland, OR (United States); Shugard, Erin [Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA (United States); Yom, Sue S., E-mail: yoms@radonc.ucsf.edu [Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA (United States); Department of Otolaryngology—Head and Neck Surgery, University of California, San Francisco, San Francisco, CA (United States)

    2016-07-01

    Radiation of the low neck can be accomplished using split-field intensity-modulated radiation therapy (sf-IMRT) or extended-field intensity-modulated radiation therapy (ef-IMRT). We evaluated the effect of these treatment choices on target coverage and thyroid and larynx doses. Using data from 14 patients with cancers of the oropharynx, we compared the following 3 strategies for radiating the low neck: (1) extended-field IMRT, (2) traditional split-field IMRT with an initial cord-junction block to 40 Gy, followed by a full-cord block to 50 Gy, and (3) split-field IMRT with a full-cord block to 50 Gy. Patients were planned using each of these 3 techniques. To facilitate comparison, extended-field plans were normalized to deliver 50 Gy to 95% of the neck volume. Target coverage was assessed using the dose to 95% of the neck volume (D{sub 95}). Mean thyroid and larynx doses were computed. Extended-field IMRT was used as the reference arm; the mean larynx dose was 25.7 ± 7.4 Gy, and the mean thyroid dose was 28.6 ± 2.4 Gy. Split-field IMRT with 2-step blocking reduced laryngeal dose (mean larynx dose 15.2 ± 5.1 Gy) at the cost of a moderate reduction in target coverage (D{sub 95} 41.4 ± 14 Gy) and much higher thyroid dose (mean thyroid dose 44.7 ± 3.7 Gy). Split-field IMRT with initial full-cord block resulted in greater laryngeal sparing (mean larynx dose 14.2 ± 5.1 Gy) and only a moderately higher thyroid dose (mean thyroid dose 31 ± 8 Gy) but resulted in a significant reduction in target coverage (D{sub 95} 34.4 ± 15 Gy). Extended-field IMRT comprehensively covers the low neck and achieves acceptable thyroid and laryngeal sparing. Split-field IMRT with a full-cord block reduces laryngeal doses to less than 20 Gy and spares the thyroid, at the cost of substantially reduced coverage of the low neck. Traditional 2-step split-field IMRT similarly reduces the laryngeal dose but also reduces low-neck coverage and delivers very high doses to the thyroid.

  1. Optical properties of 3d-ions in crystals spectroscopy and crystal field analysis

    CERN Document Server

    Brik, Mikhail

    2013-01-01

    "Optical Properties of 3d-Ions in Crystals: Spectroscopy and Crystal Field Analysis" discusses spectral, vibronic and magnetic properties of 3d-ions in a wide range of crystals, used as active media for solid state lasers and potential candidates for this role. Crystal field calculations (including first-principles calculations of energy levels and absorption spectra) and their comparison with experimental spectra, the Jahn-Teller effect, analysis of vibronic spectra, materials science applications are systematically presented. The book is intended for researchers and graduate students in crystal spectroscopy, materials science and optical applications. Dr. N.M. Avram is an Emeritus Professor at the Physics Department, West University of Timisoara, Romania; Dr. M.G. Brik is a Professor at the Institute of Physics, University of Tartu, Estonia.

  2. The Split-field Etalon Doppler Imager (SEDI) - A Compact Thermosphere Wind Profiler

    Science.gov (United States)

    Marchant, A.; Whalen, S.; Stromberg, E. M.; Swenson, C.; Fish, C. S.

    2012-12-01

    The dynamics of the Earth's thermosphere remains an important target for scientific exploration. The primary energy input is solar EUV but during solar events additional energy is deposited into the high-latitude thermosphere in the form of Joule heating and particle precipitation, driving global changes in thermosphere temperature profiles and circulation. Thermosphere wind and temperature profiles are important factors for understanding the dynamic response of the earth system to solar storms, for building and maintaining global weather and climate models, and for making operational space weather predictions. We report progress in miniaturized sensor technology for orbital monitoring of wind and neutral temperature profiles in the upper thermosphere, 200 - 350 km. These profiles are sensed using the atomic oxygen airglow at 630.0 nm. The split-field etalon Doppler imager (SEDI) focuses forward and aft scenes of the earth limb onto a single EMCCD focal plane through a single Fabry-Perot etalon (Figure 1). The size of the SEDI optical system is 14 x 18 x 7 cm. The instrument has no moving parts and is easily packaged in a 6U CubeSat. Strips of the dual interferogram are analyzed with respect to fringe width and radial phase to yield profiles of the neutral temperature and Doppler shift. Instrument calibration is maintained on-orbit using the 630.4 nm reference line from a neon glow lamp. The prediction of Doppler sensitivity vs. tangent height against the limb is plotted in Figure 2 for a profiling resolution of 5 km. Forward-view Doppler profiles are combined with aft-view profiles collected approximately 5 minutes later to create localized 2D wind profiles. A constellation of SEDI CubeSats could provide global monitoring of the thermosphere wind field and its dynamics.; Figure 1. Layout of the SEDI instrument. ; Figure 2. Doppler sensitivity of the SEDI instrument.

  3. Crystal-field and covalency effects in uranates: an X-ray spectroscopic study

    Energy Technology Data Exchange (ETDEWEB)

    Butorin, Sergei M. [Molecular and Condensed Matter Physics, Department of Physics and Astronomy, Uppsala University, Uppsala (Sweden); Kvashnina, Kristina O. [European Synchrotron Radiation Facility, CS40220, Grenoble (France); Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, Dresden (Germany); Smith, Anna L. [Department of Radiation Science and Technology, TU Delft (Netherlands); Popa, Karin [European Commission, Joint Research Centre, Institute for Transuranium Elements, Karlsruhe (Germany); Martin, Philippe M. [CEA Marcoule, CEA, DEN, DTEC/SECA/LCC, Bagnols-sur-Ceze (France)

    2016-07-04

    The electronic structure of U{sup V}- and U{sup VI}-containing uranates NaUO{sub 3} and Pb{sub 3}UO{sub 6} was studied by using an advanced technique, namely X-ray absorption spectroscopy (XAS) in high-energy-resolution fluorescence-detection (HERFD) mode. Due to a significant reduction in core-hole lifetime broadening, the crystal-field splittings of the 5f shell were probed directly in HERFD-XAS spectra collected at the U 3d edge, which is not possible by using conventional XAS. In addition, the charge-transfer satellites that result from U 5f-O 2p hybridization were clearly resolved. The crystal-field parameters, 5f occupancy, and degree of covalency of the chemical bonding in these uranates were estimated by using the Anderson impurity model by calculating the U 3d HERFD-XAS, conventional XAS, core-to-core (U 4f-3d transitions) resonant inelastic X-ray scattering (RIXS), and U 4f X-ray photoelectron spectra. The crystal field was found to be strong in these systems and the 5f occupancy was determined to be 1.32 and 0.84 electrons in the ground state for NaUO{sub 3} and Pb{sub 3}UO{sub 6}, respectively, which indicates a significant covalent character for these compounds. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Mapping the absolute electromagnetic field strength of individual field components inside a photonic crystal

    NARCIS (Netherlands)

    Denis, T.; Reijnders, B.; Lee, J.H.H.; Vos, Willem L.; Boller, Klaus J.; van der Slot, Petrus J.M.

    2013-01-01

    We present a method to map the absolute electromagnetic field strength inside photonic crystals. We demonstrate our method by applying it to map the electric field component Ez of a two-dimensional photonic crystal slab at microwave frequencies. The slab is placed between two mirrors to create a

  5. Strong field enhancement and light-matter interactions with all-dielectric metamaterials based on split bar resonators.

    Science.gov (United States)

    Zhang, Jianfa; Liu, Wei; Zhu, Zhihong; Yuan, Xiaodong; Qin, Shiqiao

    2014-12-15

    Strong subwavelength field enhancement has often been assumed to be unique to plasmonic nanostructures. Here we propose a type of all-dielectric metamaterials based on split bar resonators. The nano gap at the centre of the resonant elements results in large local field enhancement and light localization in the surrounding medium, which can be employed for strong light-matter interactions. In a Fano-resonant dielectric metamaterial comprising pairs of asymmetric split silicon bars, the enhancement of electric field amplitude in the gap exceeds 120 while the averaged electromagnetic energy density is enhanced by more than 7000 times. An optical refractive index sensor with a potential sensitivity of 525 nm/RIU is designed based on the proposed metamaterials. The proposed concept can be applied to other types of dielectric nanostructures and may stimulate further research of dielectric metamaterials for applications ranging from nonlinear optics and sensing to the realization of new types of active lasing devices.

  6. Hyperfine and crystal field interactions in multiferroic HoCrO3

    Science.gov (United States)

    Kumar, C. M. N.; Xiao, Y.; Nair, H. S.; Voigt, J.; Schmitz, B.; Chatterji, T.; Jalarvo, N. H.; Brückel, Th

    2016-11-01

    We report a comprehensive specific heat and inelastic neutron scattering study to explore the possible origin of multiferroicity in HoCrO3. We have performed specific heat measurements in the temperature range 100 mK-290 K and inelastic neutron scattering measurements were performed in the temperature range 1.5-200 K. From the specific heat data we determined hyperfine splitting at 22.5(2) μeV and crystal field transitions at 1.379(5) meV, 10.37(4) meV, 15.49(9) meV and 23.44(9) meV, indicating the existence of strong hyperfine and crystal field interactions in HoCrO3. Further, an effective hyperfine field is determined to be 600(3) T. The quasielastic scattering observed in the inelastic scattering data and a large linear term γ =6.3(8) mJ mol-1  K-2 in the specific heat is attributed to the presence of short range exchange interactions, which is understood to be contributing to the observed ferroelectricity. Further the nuclear and magnetic entropies were computed to be, ˜17.2 Jmol-1 K-1 and  ˜34 Jmol-1 K-1, respectively. The entropy values are in excellent agreement with the limiting theoretical values. An anomaly is observed in the peak position of the temperature dependent crystal field spectra around 60 K, at the same temperature an anomaly in the pyroelectric current is reported. From this we could elucidate a direct correlation between the crystal electric field excitations of Ho3+ and ferroelectricity in HoCrO3. Our present study, along with recent reports, confirm that HoCrO3, and RCrO3 (R  =  rare earth) in general, possess more than one driving force for the ferroelectricity and multiferroicity.

  7. Fiber field-effect device via in situ channel crystallization.

    Science.gov (United States)

    Danto, Sylvain; Sorin, Fabien; Orf, Nicholas D; Wang, Zheng; Speakman, Scott A; Joannopoulos, John D; Fink, Yoel

    2010-10-01

    The in situ crystallization of the incorporated amorphous semiconductor within the multimaterial fiber device yields a large decrease in defect density and a concomitant five-order-of-magnitude decrease in resistivity of the novel metal-insulator-crystalline semiconductor structure. Using a post-drawing crystallization process, the first tens-of-meters-long single-fiber field-effect device is demonstrated. This work opens significant opportunities for incorporating higher functionality in functional fibers and fabrics.

  8. Phase Field Modeling of Twinning in Indentation of Transparent Crystals

    Science.gov (United States)

    2011-09-01

    twin boundaries . Equilibrium configurations of deformed and twinned crystals are attained via direct energy minimization. The theory is framed in the...phases: (i) the original crystal (the parent) and (ii) the twin. Interfaces between phases are twin boundaries . Order parameter η generally exhibits the...following values: η(X, •) = 0∀X ∈ parent, = 1∀X ∈ twin, ∈ (0, 1)∀X ∈ twin boundaries . (1) In linear elasticity, kinematic field variables are

  9. Magnetic Fields and the Crystallization of White Dwarfs

    Science.gov (United States)

    Isern, J.; García-Berro, E.; Külebi, B.; Lorén-Aguilar, P.

    2017-03-01

    The evolution of white dwarfs can be described as a cooling process. When the temperature is low enough, the interior experiences a phase transition and crystallizes. Crystallization introduces two new sources of energy, latent heat and chemical sedimentation, and induces the formation of a convective mantle around the solid core. This structure, which is analogous to that of the Earth, could induce the formation of a magnetic field via dynamo mechanism. In this work we discuss the viability of such mechanism, and its use as a diagnostic tool of crystallization.

  10. Crystal field spectra of lunar pyroxenes.

    Science.gov (United States)

    Burns, R. G.; Abu-Eid, R. M.; Huggins, F. E.

    1972-01-01

    Absorption spectra in the visible and near infrared regions have been obtained for pyroxene single crystals in rocks from the Apollo 11, 12, 14, and 15 missions. The polarized spectra are compared with those obtained from terrestrial calcic clinopyroxenes, subcalcic augites, pigeonites, and orthopyroxenes. The lunar pyroxenes contain several broad, intense absorption bands in the near infrared, the positions of which are related to bulk composition, Fe(2+) site occupancy and structure type of the pyroxene. The visible spectra contain several sharp, weak peaks mainly due to spin-forbidden transitions in Fe(2+). Additional weak bands in this region in Apollo 11 pyroxenes are attributed to Ti(3+) ions. Spectral features from Fe(3+), Mn(2+), Cr(3+), and Cr(2+) were not observed.

  11. Theoretical Calculations of Thermal Shifts of Ground-State Zero-Field-Splitting for Ruby

    Institute of Scientific and Technical Information of China (English)

    MA Dong-Ping; CHEN Ju-Rong; MA Ning

    2001-01-01

    By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of wavefunctions within d3 electronic configuration, the thermal shifts (TS) of the ground-state zero-field-splitting (GSZFS) due to EPI for ruby have microscopic-theoretically been calculated; the contribution to TS of GSZFS from thermal expansion has also been calculated. The results are in very good agreement with experiments. It is found that the contributions from the first-order perturbation of the second-order term in EPI Hamiltonian are dominant in the Raman term and optical-branch term for TS of GSZFS; the different between the TS due to EPI oft3 2 4A2 ± 1/2e2 (G2) level and the TS due to EPI oft32 4A2 ± 3/2e2 (Gl) level gives riseto the TS due to EPI of GSZFS, which is very small in comparison with the TS due to EPI of G2 or G1 level. Among various terms in TS of GSZFS, Raman term is the largest one and the signs of the Raman term and optical-branch term are opposite to the sign of the thermal-expansion term; the optical-branch term plays an important role in TS of GSZFS and increases rapidly with temperature; all various contributions to TS of GSZFS have to be taken into account, since the subtle balance among them determines the total result. The comparison between the features of TS of GSZFS and those of TS of R1 and R2 lines has been made. For TS of GSZFS, the contribution from thermal expansion is especially important; the neighbor-level term is insignificant.``

  12. A density functional theory study of the zero-field splitting in high-spin nitrenes

    Science.gov (United States)

    Misochko, Eugenii Ya.; Korchagin, Denis V.; Bozhenko, Konstantin V.; Chapyshev, Sergei V.; Aldoshin, Sergei M.

    2010-08-01

    This work presents a detailed evaluation of the performance of density functional theory (DFT) for the prediction of zero-field splittings (ZFSs) in high-spin nitrenes. A number of well experimentally characterized triplet mononitrenes, quartet nitrenoradicals, quintet dinitrenes, and septet trinitrenes have been considered. Several DFT-based approaches for the prediction of ZFSs have been compared. It is shown that the unrestricted Kohn-Sham and the Pederson-Khanna approaches are the most successful for the estimation of the direct spin-spin (SS) interaction and the spin-orbit coupling (SOC) parts, respectively, to the final ZFS parameters. The most accurate theoretical predictions (within 10%) are achieved by using the PBE density functional in combination with the DZ, EPR-II, and TZV basis sets. For high-spin nitrenes constituted from light atoms, the contribution of the SOC part to ZFS parameters is quite small (7%-12%). By contrast, for chlorine-substituted septet trinitrenes, the contribution of the SOC part is small only to D value but, in the case of E value, it is as large as the SS part and has opposite sign. Due to this partial cancellation of two different contributions, SS and SOC, the resulting values of E in heavy molecules are almost two times smaller than those predicted by analysis of the widely used semiempirical one-center spin-spin interaction model. The decomposition of DSS into n-center (n =1-4) interactions shows that the major contribution to DSS results from the one-center spin-spin interactions. This fact indicates that the semiempirical SS interaction model accurately predicts the ZFS parameters for all types of high-spin nitrenes with total spin S =2 and 3, if their molecules are constructed from the first-row atoms.

  13. Magnetic Field Applications in Semiconductor Crystal Growth and Metallurgy

    Science.gov (United States)

    Mazuruk, Konstantin; Ramachandran, Narayanan; Grugel, Richard; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The Traveling Magnetic Field (TMF) technique, recently proposed to control meridional flow in electrically conducting melts, is reviewed. In particular, the natural convection damping capability of this technique has been numerically demonstrated with the implication of significantly improving crystal quality. Advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, are discussed. Finally, results of experiments with mixing metallic alloys in long ampoules using TMF is presented

  14. Correlation theory of crystal field and anisotropic exchange effects

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker

    1985-01-01

    A general theory for including correlation effects in static and dynamic properties is presented in terms of Raccah or Stevens operators. It is explicitly developed for general crystal fields and anisotropic interactions and systems with several sublattices, like the rare earth compounds. The the......A general theory for including correlation effects in static and dynamic properties is presented in terms of Raccah or Stevens operators. It is explicitly developed for general crystal fields and anisotropic interactions and systems with several sublattices, like the rare earth compounds....... The theory gives explicitly a temperature dependent renormalization of both the crystal field and the interactions, and a damping of the excitations and in addition a central park component. The general theory is illustrated by a discussion of the singlet-doublet system. The correlation effects...... on the susceptibility, the first and second moment frequencies and the line shape are calculated self-consistently....

  15. Relaxation Dynamics of Ferroelectric Liquid Crystals in Pulsed Electric Field

    Science.gov (United States)

    Kudreyko, A. A.; Migranov, N. G.; Migranova, D. N.

    2016-11-01

    In this contribution we report a theoretical study of relaxation processes in surface-stabilized ferroelectric liquid crystals with spontaneous polarization. The influence of pulsed electric field on the behavior of ferroelectric liquid crystal in the SmC* phase, which is placed in a thin cell with strong anchoring of SmC* molecules with the boundary substrate, is studied. In the vicinity of the substrate interface, temporal dependence of the azimuthal motion of the director induced by electric field is obtained. The response to the external distortion of ferroelectric liquid crystal confined between two microstructured substrates is the occurrence of periodic temporal formation of solitons connected with the distortion of the director field n in the sample bulk. The interplay between microstructured substrates and director distribution of the ferroelectric SmC* phase is explained by the Frenkel-Kontorova model for a chain of atoms, but adapted for the continuum problem.

  16. Physical modelling of Czochralski crystal growth in horizontal magnetic field

    Science.gov (United States)

    Grants, Ilmārs; Pal, Josef; Gerbeth, Gunter

    2017-07-01

    This study addresses experimentally the heat transfer, the temperature azimuthal non-uniformity and the onset of oscillations in a low temperature physical model of a medium-sized Czochralski crystal growth process with a strong horizontal magnetic field (HMF). It is observed that under certain conditions the integral heat flux may decrease with increasing magnetic field strength at the same time as the flow velocity increases. The azimuthal non-uniformity of the temperature field in the melt near the crystal model rim is only little influenced by its rotation rate outside of a narrow range where the centrifugal force balances the buoyant one. The flow oscillation onset has been observed for two values of the HMF strength. Conditions of this onset are little influenced by the crystal rotation. The critical temperature difference of the oscillation onset considerably exceeds that of the Rayleigh-Bénard (RB) cell in a strong HMF.

  17. CRYSTAL-FIELD AND TRANSVERSE-FIELD EFFECTS OF THE SPIN-ONE ISING MODEL

    Institute of Scientific and Technical Information of China (English)

    宋为基; 杨传章

    1993-01-01

    A mean-field approximation (MFA) is used to treat the crystal-field and transverse-field effects of the spin-1 Ising modle in the presence of longitudinal field. In spite of its simplicity, this scheme still gives the satisfied results.

  18. Chiral Symmetry Breaking and Point-Splitting Procedure in Light-Cone Quantized QED in a Magnetic Field

    CERN Document Server

    Steinbacher, D

    2005-01-01

    The summation of all rainbow diagrams in QED in a strong magnetic field leads to a dynamical electron mass on the light-cone. Further contributions to this summation however can cause problems with light-cone singularities. It is shown that these problems are generally avoided by applying the point-splitting regularization to every diagram. The possibility of implementing this procedure into the Lagrangian of the theory is discussed.

  19. Organic single-crystal field-effect transistors

    Directory of Open Access Journals (Sweden)

    Colin Reese

    2007-03-01

    Full Text Available Organic molecular crystals hold great promise for the rational development of organic semiconductor materials. Their long-range order not only reveals the performance limits of organic materials, but also provides unique insight into their intrinsic transport properties. The field-effect transistor (FET has served as a versatile tool for electrical characterization of many facets of their performance. In the last few years, breakthroughs in single-crystal FET fabrication techniques have enabled the realization of field-effect mobilities far surpassing amorphous Si, observation of the Hall effect in an organic material, and the study of transport as an explicit function of molecular packing and chemical structure.

  20. Fine structure of fields in 2D photonic crystal waveguides

    DEFF Research Database (Denmark)

    Lavrinenko, Andrei; Volkov, V. S.; Bozhevolnyi, S. I.

    2006-01-01

    We resolve fine structure of fields in a single-row missing photonic crystal waveguide by finite-difference time-domain modelling and SNOM measurements. Both linear dispersion and slow-light regimes in proximity of the cutoff are addressed in the analysis.......We resolve fine structure of fields in a single-row missing photonic crystal waveguide by finite-difference time-domain modelling and SNOM measurements. Both linear dispersion and slow-light regimes in proximity of the cutoff are addressed in the analysis....

  1. Electromagnetic Field Effects in Semiconductor Crystal Growth

    Science.gov (United States)

    Dulikravich, George S.

    1996-01-01

    This proposed two-year research project was to involve development of an analytical model, a numerical algorithm for its integration, and a software for the analysis of a solidification process under the influence of electric and magnetic fields in microgravity. Due to the complexity of the analytical model that was developed and its boundary conditions, only a preliminary version of the numerical algorithm was developed while the development of the software package was not completed.

  2. Electromagnetic field patterning or crystal light

    Science.gov (United States)

    Słupski, Piotr; Wymysłowski, Artur; Czarczyński, Wojciech

    2016-12-01

    Using the orbital angular momentum of light for the development of a vortex interferometer, the underlying physics requires microwave/RF models,1 as well as quantum mechanics for light1, 2 and fluid flow for semiconductor devices.3, 4 The combination of the aforementioned physical models yields simulations and results such as optical lattices,1 or an Inverse Farday effect.5 The latter is explained as the absorption of optical angular momentum, generating extremely high instantenous magnetic fields due to radiation friction. An algorithmic reduction across the computational methods used in microwaves, lasers, quantum optics and holography is performed in order to explain electromagnetic field interactions in a single computational framework. This work presents a computational model for photon-electron interactions, being a simplified gauge theory described using differentials or disturbances (photons) instead of integrals or fields. The model is based on treating the Z-axis variables as a Laplace fluid with spatial harmonics, and the XY plane as Maxwell's equations on boundaries. The result is a unified, coherent, graphical computational method of describing the photon qualitatively, quantitatively and with proportion. The model relies on five variables and is described using two equations, which use emitted power, cavity wavelength, input frequency, phase and time. Phase is treated as a rotated physical dimension under gauge theory of Feynmann's QED. In essence, this model allows the electromagnetic field to be treated with it's specific crystallography. The model itself is described in Python programming language. PACS 42.50.Pq, 31.30.J-, 03.70.+k, 11.10.-z, 67.10.Hk

  3. Splitting of quantum information in travelling wave fields using only linear optical elements

    Energy Technology Data Exchange (ETDEWEB)

    Cardoso, W B; De Almeida, N G; Avelar, A T; Baseia, B [Instituto de Fisica, Universidade Federal de Goias, 74.001-970, Goiania-GO (Brazil)

    2011-02-28

    In this paper we present a feasible post-selection scheme to split quantum information in the realm of travelling waves with success probability of 50%. Taking advantage of this scheme we have also proposed the generation of a class of W states useful for perfect teleportation and superdense coding. The scheme employs only linear optical elements as beam splitters (BS) and phase shifters, plus two photon counters and a source of two spontaneous parametric down-conversion photons. It is shown that splitting of quantum information with high fidelity is possible, even when using inefficient detectors and photoabsorption BS.

  4. Improving NASICON Sinterability through Crystallization under High Frequency Electrical Fields

    Directory of Open Access Journals (Sweden)

    Ilya eLisenker

    2016-03-01

    Full Text Available The effect of high frequency (HF electric fields on the crystallization and sintering rates of a lithium aluminum germanium phosphate (LAGP ion conducting ceramic was investigated. LAGP with the nominal composition Li1.5Al0.5Ge1.5(PO43 was crystallized and sintered, both conventionally and under effect of electrical field. Electrical field application, of 300V/cm at 1MHz, produced up to a 40% improvement in sintering rate of LAGP that was crystallized and sintered under the HF field. Heat sink effect of the electrodes appears to arrest thermal runaway and subsequent flash behavior. Sintered pellets were characterized using XRD, SEM, TEM and EIS to compare conventionally and field sintered processes. The as-sintered structure appears largely unaffected by the field as the sintering curves tend to converge beyond initial stages of sintering. Differences in densities and microstructure after 1 hour of sintering were minor with measured sintering strains of 31% vs. 26% with and without field, respectively . Ionic conductivity of the sintered pellets was evaluated and no deterioration due to the use of HF field was noted, though capacitance of grain boundaries due to secondary phases was significantly increased.

  5. Crystallization of Calcium Carbonate in a Large Scale Field Study

    Science.gov (United States)

    Ueckert, Martina; Wismeth, Carina; Baumann, Thomas

    2017-04-01

    The long term efficiency of geothermal facilities and aquifer thermal energy storage in the carbonaceous Malm aquifer in the Bavarian Molasse Basin is seriously affected by precipitations of carbonates. This is mainly caused by pressure and temperature changes leading to oversaturation during production. Crystallization starts with polymorphic nuclei of calcium carbonate and is often described as diffusion-reaction controlled. Here, calcite crystallization is favoured by high concentration gradients while aragonite crystallization is occurring at high reaction rates. The factors affecting the crystallization processes have been described for simplified, well controlled laboratory experiments, the knowledge about the behaviour in more complex natural systems is still limited. The crystallization process of the polymorphic forms of calcium carbonate were investigated during a heat storage test at our test site in the eastern part of the Bavarian Molasse Basin. Complementary laboratory experiments in an autoclave were run. Both, field and laboratory experiments were conducted with carbonaceous tap water. Within the laboratory experiments additionally ultra pure water was used. To avoid precipitations of the tap water, a calculated amount of {CO_2} was added prior to heating the water from 45 - 110°C (laboratory) resp. 65 - 110°C (field). A total water volume of 0.5 L (laboratory) resp. 1 L (field) was immediately sampled and filtrated through 10 - 0.1

  6. Crystal Field Parameters and Phase Transitions in ErSb

    DEFF Research Database (Denmark)

    Shapiro, S. M.; Bak, P.

    1975-01-01

    The crystal field levels of the Er ion in a single crystal of ErSb have been measured by inelastic neutron scattering. The crystal field parameters obtained by a least squares fit to the spectra at several temperatures are: B4 = (0·473 ± 0·005) × 10−2°K and B6 = (0·59 ± 0·06) × 10−5°K, which differ...... considerably from the values o by interpolation from measurements on other compounds. In addition the temperature dependence of the magnetic scattering in the vicinity of the Néel temperature (TN = 3·55°K) clearly demonstrates that the transition is second order in contrast to the first order behavior...

  7. Tailor-made force fields for crystal-structure prediction.

    Science.gov (United States)

    Neumann, Marcus A

    2008-08-14

    A general procedure is presented to derive a complete set of force-field parameters for flexible molecules in the crystalline state on a case-by-case basis. The force-field parameters are fitted to the electrostatic potential as well as to accurate energies and forces generated by means of a hybrid method that combines solid-state density functional theory (DFT) calculations with an empirical van der Waals correction. All DFT calculations are carried out with the VASP program. The mathematical structure of the force field, the generation of reference data, the choice of the figure of merit, the optimization algorithm, and the parameter-refinement strategy are discussed in detail. The approach is applied to cyclohexane-1,4-dione, a small flexible ring. The tailor-made force field obtained for cyclohexane-1,4-dione is used to search for low-energy crystal packings in all 230 space groups with one molecule per asymmetric unit, and the most stable crystal structures are reoptimized in a second step with the hybrid method. The experimental crystal structure is found as the most stable predicted crystal structure both with the tailor-made force field and the hybrid method. The same methodology has also been applied successfully to the four compounds of the fourth CCDC blind test on crystal-structure prediction. For the five aforementioned compounds, the root-mean-square deviations between lattice energies calculated with the tailor-made force fields and the hybrid method range from 0.024 to 0.053 kcal/mol per atom around an average value of 0.034 kcal/mol per atom.

  8. Optical antenna of comb-shaped split ring architecture for increased field localization in NIR and MIR.

    Science.gov (United States)

    Kilic, Veli Tayfun; Erturk, Vakur B; Demir, Hilmi Volkan

    2013-12-02

    We propose and demonstrate novel designs of optical antennas based on comb-shaped split ring architecture that display multi resonance field intensity enhancement spectrum. These nanoantennas achieve substantially increased field localization at longer wavelengths than that of a single or an array of dipoles with the same side length. With these optical antennas, localizing near infrared (NIR) and mid infrared (MIR) lights within a region of tens of nanometers at an intensity enhancement level of the order of thousands of magnitude can be accomplished.

  9. Fine structure of fields in 2D photonic crystal waveguides

    DEFF Research Database (Denmark)

    Lavrinenko, Andrei; Volkov, V. S.; Bozhevolnyi, S. I.

    2006-01-01

    We resolve fine structure of fields in a single-row missing photonic crystal waveguide by finite-difference time-domain modelling and SNOM measurements. Both linear dispersion and slow-light regimes in proximity of the cutoff are addressed in the analysis....

  10. Control over colloidal crystallization by shear and electric fields

    NARCIS (Netherlands)

    Wu, Y.L.

    2007-01-01

    We used shear flow and an electric field to control colloidal crystallization. The structures were examined in situ with confocal microscopy. For experiments under shear, a new parallel plate shear cell was designed. It had a zero-velocity plane that was stationary with respect to the microscope. Th

  11. Crystal orientation effects on wurtzite quantum well electromechanical fields

    DEFF Research Database (Denmark)

    Duggen, Lars; Willatzen, Morten

    2010-01-01

    A one-dimensional continuum model for calculating strain and electric field in wurtzite semiconductor heterostructures with arbitrary crystal orientation is presented and applied to GaN/AlGaN and ZnO/MgZnO heterostructure combinations. The model is self-consistent involving feedback couplings of ...

  12. Field-effect transistors on tetracene single crystals

    NARCIS (Netherlands)

    De Boer, R.W.I.; Klapwijk, T.M.; Morpurgo, A.F

    2003-01-01

    We report on the fabrication and electrical characterization of field-effect transistors at the surface of tetracene single crystals. We find that the mobility of these transistors reaches the room-temperature value of 0.4 cm2/V s. The nonmonotonous temperature dependence of the mobility, its weak g

  13. Phase field simulations of ice crystal growth in sugar solutions

    NARCIS (Netherlands)

    Sman, Van Der R.G.M.

    2016-01-01

    We present the first model ever, that describes explicitly ice crystal growth in a sugar solution during freezing. This 2-D model uses the phase field method, supplemented with realistic, and predictive theories on the thermodynamics and (diffusion) kinetics of this food system. We have to make u

  14. Field stability of piezoelectric shear properties in PIN-PMN-PT crystals under large drive field.

    Science.gov (United States)

    Zhang, Shujun; Li, Fei; Luo, Jun; Xia, Ru; Hackenberger, Wesley; Shrout, Thomas

    2011-02-01

    The coercive fields (E(C)) of Pb(In₀.₅Nb₀.₅)O₃-Pb(Mg(¹/₃)Nb(²/₃)O₃-PbTiO₃ (PIN-PMN-PT) ternary single crystals were found to be 5 kV/cm, double the value of binary Pb(Mg(¹/₃)Nb(²/₃)O₃-PbTiO₃ (PMNT) crystals, further increased to 6 to 9 kV/cm using Mn modifications. In addition to an increased EC, the acceptor modification resulted in the developed internal bias (E(int)), on the order of ~1 kV/cm. The piezoelectric shear properties of unmodified and Mn-modified PIN-PMN-PT crystals with various domain configurations were investigated. The shear piezoelectric coefficients and electromechanical coupling factors for different domain configurations were found to be >2000 pC/N and >0.85, respectively, with slightly reduced properties observed in Mn-modified tetragonal crystals. Fatigue/cycling tests performed on shearmode samples as a function of ac drive field level demonstrated that the allowable ac field levels (the maximum applied ac field before the occurrence of depolarization) were only ~2 kV/cm for unmodified crystals, less than half of their coercive field. Allowable ac drive levels were on the order of 4 to 6 kV/cm for Mn-modified crystals with rhombohedral/orthorhombic phase, further increased to 5 to 8 kV/cm in tetragonal crystals, because of their higher coercive fields. It is of particular interest that the allowable ac drive field level for Mn-modified crystals was found to be ≥ 60% of their coercive fields, because of the developed E(int), induced by the acceptor-oxygen vacancy defect dipoles.

  15. Organic field-effect transistors using single crystals

    Directory of Open Access Journals (Sweden)

    Tatsuo Hasegawa and Jun Takeya

    2009-01-01

    Full Text Available Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs, the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20–40 cm2 Vs−1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.

  16. TOPICAL REVIEW: Organic field-effect transistors using single crystals

    Science.gov (United States)

    Hasegawa, Tatsuo; Takeya, Jun

    2009-04-01

    Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20-40 cm2 Vs-1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.

  17. Effective-Field Theory on High Spin Systems with Biaxial Crystal Field

    Institute of Scientific and Technical Information of China (English)

    JIANG Wei; GUO An-Bang; LI Xin; WANG Xi-Kun; BAI Bao-Dong

    2006-01-01

    Based on the effective-field theory with self-spin correlations and the differential operator technique,physical properties of the spin-2 system with biaxial crystal field on the simple cubic, body-centered cubic, as well as faced-centered lattice have been studied. The influences of the external longitudinal magnetic field on the magnetization,internal energy, specific heat, and susceptibility have been discussed in detail. The phenomenon that the magnetization in the ground state shows quantum effects produced by the biaxial transverse crystal field has been found.

  18. Near-field probing of photonic crystal directional couplers

    DEFF Research Database (Denmark)

    Volkov, V. S.; Bozhevolnyi, S. I.; Borel, Peter Ingo

    2006-01-01

    . By comparing the near-field optical images recorded in and after the directional coupler area, the features of light distribution are analyzed. Finally, the scanning near-field optical microscope observations are found to be in agreement with the transmission measurements conducted with the same sample.......We report the design, fabrication and characterization of a photonic crystal directional with a size of ~20 x 20 mm2 fabricated in silicon-on-insulator material. Using a scanning near-field optical microscope we demonstrate a high coupling efficiency for TM polarized light at telecom wavelengths...

  19. Full splitting of the first zero-field steps in the I-V curve of Josephson junctions of intermediate length

    DEFF Research Database (Denmark)

    Hansen, Jørn Bindslev; Divin, Yu. Ya.; Mygind, Jesper

    1986-01-01

    We report on the observation of full splitting of the first zero-field steps in the I-V curves of Josephson transmission lines of intermediate length L≊(3–5)λJ, where λJ is the Josephson penetration length. We study in detail how this splitting of the step into two branches depends...... on the temperature of the junction and on a weak applied magnetic field. We relate the splitting to excitations in the junctions whose behavior is described by the perturbed sine-Gordon equation....

  20. Crystal electric field effects and thermal expansion of rare-earth hexaborides

    Science.gov (United States)

    Novikov, V. V.; Pilipenko, E. S.; Bud'ko, S. L.

    2017-02-01

    Anomalies in the magnetic contribution to the thermal expansion coefficients ∆β(T)of the CeB6, PrB6, and NdB6 hexaborides in the range of 5-300 K were found by comparison with diamagnetic LaB6. The characteristic of the anomalies was the same in all the studied borides: a distinct peak at low temperatures, followed by a broad maximum at higher temperatures (50-100 K), then a decrease and transition to the region of negative values as the temperature increases further. The features of ∆β(T) are explained by the effects of the magnetic order (sharp low temperature peaks) and the crystal electric field (CEF). The βCEF(T) dependencies were calculated using Raman and neutron scattering data on the splitting of the rare-earth (RE) ions R3+ f-level by the CEF. A satisfactory consistency between the values of βCEF(T) and ∆β(T)was obtained for the studied hexaborides. Additionally, we determined the values of the Grüneisen parameter γi that correspond to the transition between the ground and excited multiplets of R3+ ions f-level splitting.

  1. Spectroscopic and crystal-field analysis of new Yb-doped laser materials

    Energy Technology Data Exchange (ETDEWEB)

    Haumesser, Paul-Henri; Gaume, Romain; Antic-Fidancev, Elisabeth; Vivien, Daniel; Viana, Bruno [Laboratoire de Chimie Appliquee de l' Etat Solide UMR 75 74, ENSCP, Paris (France)]. E-mail: viana@ext.jussieu.fr

    2001-06-11

    Crystal-field effects are very important as far as laser performances of Yb-doped materials are concerned. In order to simplify the interpretation of low-temperature spectra, two tools derived from a careful examination of crystal-field interaction are presented. Both approaches are successfully applied in the case of new Yb-doped materials, namely Ca{sub 3}Y{sub 2}(BO{sub 3}){sub 4} (CYB), Ca{sub 3}Gd{sub 2}(BO{sub 3}){sub 4} (CaGB), Sr{sub 3}Y(BO{sub 3}){sub 3} (SrYBO), Ba{sub 3}Lu(BO{sub 3}){sub 3} (BLuB), Y{sub 2}SiO{sub 5} (YSO), Ca{sub 2}Al{sub 2}SiO{sub 7} (CAS) and SrY{sub 4}(SiO{sub 4}){sub 3}O (SYS). The {sup 2}F{sub 7/2} splitting is particularly large in these materials and favourable to a quasi-three-level laser operating scheme. Calculations performed using the point charge electrostatic model for these compounds and using a consistent set of effective atomic charges confirm the experimental results. This should permit to use this model in a predictive approach. (author)

  2. Magnetic excitations in metalloporphyrins by inelastic neutron scattering: determination of zero-field splittings in iron, manganese, and chromium complexes.

    Science.gov (United States)

    Hunter, Seth C; Podlesnyak, Andrey A; Xue, Zi-Ling

    2014-02-17

    Zero field splitting (ZFS) parameters of several nondeuterated metalloporphyrins [M(TPP)Cl] and [Mn(TPP)] (H2TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are the following: D = 6.33(8) cm(-1) for [Fe(TPP)Cl], -2.24(3) cm(-1) for [Mn(TPP)Cl], 0.79(2) cm(-1) for [Mn(TPP)], and |D|= 0.234(12) cm(-1) for [Cr(TPP)Cl]. The work shows that compounds with magnetic excitations below ∼30 cm(-1) could be determined using nondeuterated samples.

  3. Plasmonic gold nanocrystals coupled with photonic crystal seamlessly on TiO2 nanotube photoelectrodes for efficient visible light photoelectrochemical water splitting

    KAUST Repository

    Zhang, Zhonghai

    2013-01-09

    A visible light responsive plasmonic photocatalytic composite material is designed by rationally selecting Au nanocrystals and assembling them with the TiO2-based photonic crystal substrate. The selection of the Au nanocrystals is so that their surface plasmonic resonance (SPR) wavelength matches the photonic band gap of the photonic crystal and thus that the SPR of the Au receives remarkable assistance from the photonic crystal substrate. The design of the composite material is expected to significantly increase the Au SPR intensity and consequently boost the hot electron injection from the Au nanocrystals into the conduction band of TiO2, leading to a considerably enhanced water splitting performance of the material under visible light. A proof-of-concept example is provided by assembling 20 nm Au nanocrystals, with a SPR peak at 556 nm, onto the photonic crystal which is seamlessly connected on TiO2 nanotube array. Under visible light illumination (>420 nm), the designed material produced a photocurrent density of ∼150 μA cm-2, which is the highest value ever reported in any plasmonic Au/TiO2 system under visible light irradiation due to the photonic crystal-assisted SPR. This work contributes to the rational design of the visible light responsive plasmonic photocatalytic composite material based on wide band gap metal oxides for photoelectrochemical applications. © 2012 American Chemical Society.

  4. Unravelling the zero-field-splitting parameters in Pt-rich polymers with tuned spin-orbit coupling

    Science.gov (United States)

    Peroncik, Peter; McLaughlin, Ryan; Sun, Dali; Vardeny, Z. Valy

    2014-03-01

    Recently pi-conjugated polymers that contain heavy metal Platinum (Pt-polymers, Scientific Reports 3, 2653, 2013) have attracted substantial interest due to their strong and tunable spin-orbit coupling (SOC). The magnetic field effect (MFE), such as magneto-photoluminescence (MPL) is considered to be a viable approach to address the SOC strength in the organics. Alas conventional MFE up to several hundred Gauss is unable to overcome the relative large spin splitting energies in Pt-polymers due to their strong SOC. To overcome this difficulty we study the MPL response in two Pt-polymers at high magnetic field (up to several Telsa). We found that the MPL response is dominated by triplet excitons that are generated in record time, and from the MPL(B) response width we could obtained the triplet zero-field splitting (ZFS) parameters. We found that the ZFS parameters in the Pt-polymers are proportional to the intrachain Pt atom concentration. Research sponsored by the NSF (Grant No. DMR-1104495) and NSF-MRSEC (DMR 1121252) at the University of Utah.

  5. Embryo splitting

    Directory of Open Access Journals (Sweden)

    Karl Illmensee

    2010-04-01

    Full Text Available Mammalian embryo splitting has successfully been established in farm animals. Embryo splitting is safely and efficiently used for assisted reproduction in several livestock species. In the mouse, efficient embryo splitting as well as single blastomere cloning have been developed in this animal system. In nonhuman primates embryo splitting has resulted in several pregnancies. Human embryo splitting has been reported recently. Microsurgical embryo splitting under Institutional Review Board approval has been carried out to determine its efficiency for blastocyst development. Embryo splitting at the 6–8 cell stage provided a much higher developmental efficiency compared to splitting at the 2–5 cell stage. Embryo splitting may be advantageous for providing additional embryos to be cryopreserved and for patients with low response to hormonal stimulation in assisted reproduction programs. Social and ethical issues concerning embryo splitting are included regarding ethics committee guidelines. Prognostic perspectives are presented for human embryo splitting in reproductive medicine.

  6. Exchange Enhancement of Spin-Splitting in AlxGa1-xN/GaN Heterostructures in Tilted Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    TANG Ning; HAN Kui; LU Fang-Chao; DUAN Jun-Xi; XU Fu-Jun; SHEN Bo

    2011-01-01

    Alx Ga1-xN/GaN heterostructures are investigated by magnetotransport experiments in tilted magnetic fields at low temperatures.The spin-split peaks of the Shubnikov-de Haas(SdH)oscillations are observed at high magnetic fields, which are attributed to the Zeeman spin-splitting of the two-dimensional electron gas at the heterointerface. The exchange enhanced g* of the spin-splitting is investigated by measuring the positions of the pairs of spin-split SdH maxima. Moreover, it is found that g* becomes smaller with the increasing tilt angle,which suggests the anisotropy of g* is due to the strong polarization-induced electric field at the Alx Ga1-xN/GaN heterointerface.

  7. Orientation ordering in J = 1 solid hydrogens at crystal fields

    CERN Document Server

    Antsygina, T N; Freimann, Y A; Hemley, R J

    2003-01-01

    A system of quantum linear rotators with a rotational quantum number J 1 is considered at a crystal field. An equation for orientation order parameter is derived, and the critical parameters, the phase separation curve and the lines of overheating and overcooling points are obtained. It is shown that in terms of the thermodynamics the behavior of the above linear rotators in the classical case and in the extremely quantum (J = 1) one is identical. For positive values of the crystal field there also exist parallels between orientation phase transitions in a system of rotators with J = 1 and phase transitions in a liquid-vapor system. It is shown that the consideration of J > 1 states results in a radical change of the phase transition behavior in a system of rotators: instead of the sole critical point typical for the J = 1 system, there appears a line of critical points.

  8. Magnetic Field Measurements Based on Terfenol Coated Photonic Crystal Fibers

    Directory of Open Access Journals (Sweden)

    Carla C. Kato

    2011-11-01

    Full Text Available A magnetic field sensor based on the integration of a high birefringence photonic crystal fiber and a composite material made of Terfenol particles and an epoxy resin is proposed. An in-fiber modal interferometer is assembled by evenly exciting both eigenemodes of the HiBi fiber. Changes in the cavity length as well as the effective refractive index are induced by exposing the sensor head to magnetic fields. The magnetic field sensor has a sensitivity of 0.006 (nm/mT over a range from 0 to 300 mT with a resolution about ±1 mT. A fiber Bragg grating magnetic field sensor is also fabricated and employed to characterize the response of Terfenol composite to the magnetic field.

  9. Magnetic field measurements based on Terfenol coated photonic crystal fibers.

    Science.gov (United States)

    Quintero, Sully M M; Martelli, Cicero; Braga, Arthur M B; Valente, Luiz C G; Kato, Carla C

    2011-01-01

    A magnetic field sensor based on the integration of a high birefringence photonic crystal fiber and a composite material made of Terfenol particles and an epoxy resin is proposed. An in-fiber modal interferometer is assembled by evenly exciting both eigenemodes of the HiBi fiber. Changes in the cavity length as well as the effective refractive index are induced by exposing the sensor head to magnetic fields. The magnetic field sensor has a sensitivity of 0.006 (nm/mT) over a range from 0 to 300 mT with a resolution about ±1 mT. A fiber Bragg grating magnetic field sensor is also fabricated and employed to characterize the response of Terfenol composite to the magnetic field.

  10. Zero-field splitting of the first excited triplet state in biradicals estimated from magnetic effects on the fluorescence decays

    Energy Technology Data Exchange (ETDEWEB)

    LeJeune, V.; Despres, A.; Migirdicyan, E. (Universite Paris-Sud, Orsay (France))

    1990-12-27

    The fluorescence decay of matrix-isolated m-xylylene biradicals is nonexponential and attributed to the emission from different sublevels of the first excited triplet state. In the presence of a magnetic field, the lifetime of the slow decay component decreases. Its dependence as a function of a weak magnetic field can be calculated for different values of the zero-field splitting parameter D. The best fitting value is {vert bar}D{vert bar} = 0.04 {plus minus} 0.01 cm{sup {minus}1}. This D value is found to be significantly larger in the first excited triplet state than in the ground state of the m-xylylene biradicals.

  11. Low-frequency electromagnetic field in a Wigner crystal

    CERN Document Server

    Stupka, Anton

    2016-01-01

    Long-wave low-frequency oscillations are described in a Wigner crystal by generalization of the reverse continuum model for the case of electronic lattice. The internal self-consistent long-wave electromagnetic field is used to describe the collective motions in the system. The eigenvectors and eigenvalues of the obtained system of equations are derived. The velocities of longitudinal and transversal sound waves are found.

  12. Semiconductor Crystal Growth in Static and Rotating Magnetic fields

    Science.gov (United States)

    Volz, Martin

    2004-01-01

    Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a

  13. Order by virtual crystal field fluctuations in pyrochlore XY antiferromagnets

    Science.gov (United States)

    Rau, Jeffrey G.; Petit, Sylvain; Gingras, Michel J. P.

    2016-05-01

    Conclusive evidence of order by disorder is scarce in real materials. Perhaps one of the strongest cases presented has been for the pyrochlore XY antiferromagnet Er2Ti2O7 , with the ground state selection proceeding by order by disorder induced through the effects of quantum fluctuations. This identification assumes the smallness of the effect of virtual crystal field fluctuations that could provide an alternative route to picking the ground state. Here we show that this order by virtual crystal field fluctuations is not only significant, but competitive with the effects of quantum fluctuations. Further, we argue that higher-multipolar interactions that are generically present in rare-earth magnets can dramatically enhance this effect. From a simplified bilinear-biquadratic model of these multipolar interactions, we show how the virtual crystal field fluctuations manifest in Er2Ti2O7 using a combination of strong-coupling perturbation theory and the random-phase approximation. We find that the experimentally observed ψ2 state is indeed selected and the experimentally measured excitation gap can be reproduced when the bilinear and biquadratic couplings are comparable while maintaining agreement with the entire experimental spin-wave excitation spectrum. Finally, we comment on possible tests of this scenario and discuss implications for other order-by-disorder candidates in rare-earth magnets.

  14. Introduction to Phase-Field Model and Its Applications in the Fields of Crystal Growth and Planetary Science

    Science.gov (United States)

    Miura, Hitoshi; Yokoyama, Etsuro; Tsukamoto, Katsuo

    2010-07-01

    The growth of crystal induces a change of ambient environment (temperature, concentration, etc.), and the environmental change gives some feedback to the growth of crystal. The interaction between the crystal growth and ambient environment is important to be taken into consideration, also in the crystallization process of cosmic crystals observed in chondritic meteorites. In this lecture, we will introduce the phase-field simulation, which is one of the powerful numerical methods to treat the crystal growth and diffusion fields (temperature, concentration, etc.) simultaneously. Participants can experience some phase-field simulations on their own laptop by using a newly developed Java program, which will be distributed at the school.

  15. Crystal Field Levels of Pr3+ in PrFeO3 and PrGaO3 Determined by Inelastic Neutron Scattering

    DEFF Research Database (Denmark)

    Feldmann, K.; Henning, K.; Kaun, L.;

    1975-01-01

    The crystal field splitting of the 3H4 ground state of the Pr ion in PrFeO3 and PrGaO3 has been investigated by inelastic scattering of thermal neutrons. At several temperatures the transitions have been measured by TAS and TOF methods for polycrystalline PrFeO3 and by the TOF method...... for polycrystalline PrGaO3. Energy level schemes which are different for these materials are given....

  16. Calculation of the zero-field splitting tensor on the basis of hybrid density functional and Hartree-Fock theory.

    Science.gov (United States)

    Neese, Frank

    2007-10-28

    The zero-field splitting (ZFS) (expressed in terms of the D tensor) is the leading spin-Hamiltonian parameter for systems with a ground state spin S>12. To first order in perturbation theory, the ZFS arises from the direct spin-spin dipole-dipole interaction. To second order, contributions arise from spin-orbit coupling (SOC). The latter contributions are difficult to treat since the SOC mixes states of different multiplicities. This is an aspect of dominant importance for the correct prediction of the D tensor. In this work, the theory of the D tensor is discussed from the point of view of analytic derivative theory. Starting from a general earlier perturbation treatment [F. Neese and E. I. Soloman, Inorg. Chem. 37, 6568 (1998)], straightforward response equations are derived that are readily transferred to the self-consistent field (SCF) Hartree-Fock (HF) or density functional theory (DFT) framework. The main additional effort in such calculations arises from the solution of nine sets of nonstandard coupled-perturbed SCF equations. These equations have been implemented together with the spin-orbit mean-field representation of the SOC operator and a mean-field treatment of the direct spin-spin interaction into the ORCA electronic structure program. A series of test calculations on diatomic molecules with accurately known zero-field splittings shows that the new approach corrects most of the shortcomings of previous DFT based methods and, on average, leads to predictions within 10% of the experimental values. The slope of the correlation line is essentially unity for the B3LYP and BLYP functionals compared to approximately 0.5 in previous treatments.

  17. Phase-field-crystal model for fcc ordering.

    Science.gov (United States)

    Wu, Kuo-An; Adland, Ari; Karma, Alain

    2010-06-01

    We develop and analyze a two-mode phase-field-crystal model to describe fcc ordering. The model is formulated by coupling two different sets of crystal density waves corresponding to and reciprocal lattice vectors, which are chosen to form triads so as to produce a simple free-energy landscape with coexistence of crystal and liquid phases. The feasibility of the approach is demonstrated with numerical examples of polycrystalline and (111) twin growth. We use a two-mode amplitude expansion to characterize analytically the free-energy landscape of the model, identifying parameter ranges where fcc is stable or metastable with respect to bcc. In addition, we derive analytical expressions for the elastic constants for both fcc and bcc. Those expressions show that a nonvanishing amplitude of [200] density waves is essential to obtain mechanically stable fcc crystals with a nonvanishing tetragonal shear modulus (C11-C12)/2. We determine the model parameters for specific materials by fitting the peak liquid structure factor properties and solid-density wave amplitudes following the approach developed for bcc [K.-A. Wu and A. Karma, Phys. Rev. B 76, 184107 (2007)]. This procedure yields reasonable predictions of elastic constants for both bcc Fe and fcc Ni using input parameters from molecular dynamics simulations. The application of the model to two-dimensional square lattices is also briefly examined.

  18. Magnetic properties of a three layer superlattice with a crystal field

    Institute of Scientific and Technical Information of China (English)

    Jiang Wei; Li Xin; Wang Xi-Kun; Guo An-Bang

    2006-01-01

    In this paper the magnetic properties of a three layer superlattice with the crystal field on the honeycomb and square lattice have been studied based on the effective-field theory with self-spin correlations and the differential operator technique. The effects of the crystal field and longitudinal magnetic field on the susceptibility are discussed in detail. A number of interesting phenomena, originating from the competition between the longitudinal magnetic field, crystal-field,and coordination number, have been found.

  19. Optical study of crystal-field excitation in (R)Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Martin, A.A. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Inst. de Fisica ' ' Gleb Wataghin' ' , UNICAMP, Campinas-SP (Brazil); Cardona, M. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Jandl, S. [Sherbrooke Univ., PQ (Canada). Dept. de Physique; Nekvasil, V. [Inst. of Physics, Czech Academy of Sciences, Prague (Czech Republic); Wolf, T. [Forschungszentrum Karlsruhe GmbH Technik und Umwelt (Germany). Inst. fuer Technische Physik

    2000-07-01

    A large number of high-temperature superconductors (HTS) contain rare-earth (R) ions with 4f-electron multiplets which are split by the crystal field (CF) of the neighboring ligands and, in many cases, their energy differences are in the range of optical phonons. When these two excitations (phonons and CF) have the same symmetry and are close in energy they can couple to each other, leading to a doublet structure at low temperature. Since the R ions are located between the CuO{sub 2} superconducting planes, this crystal-field-phonon coupling can be used as a probe to investigate superconductivity related phenomena. In this paper, we discuss the coupling of phonons to CF excitations in (R)Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} and demonstrate that Raman and infrared spectroscopy can be successfully used as a novel tool for CF studies in HTS, since they are not limited to low energy transfer and can be applied to study small single crystals. (orig.)

  20. Phase diagram of hot QCD in an external magnetic field: possible splitting of deconfinement and chiral transitions

    CERN Document Server

    Mizher, A J; Fraga, E S

    2010-01-01

    The structure of the phase diagram for strong interactions becomes richer in the presence of a magnetic background, which enters as a new control parameter for the thermodynamics. Motivated by the relevance of this physical setting for current and future high-energy heavy ion collision experiments and for the cosmological QCD transitions, we use the linear sigma model coupled to quarks and to Polyakov loops as an effective theory to investigate how the chiral and the deconfining transitions are affected, and present a general picture for the temperature--magnetic field phase diagram. We compute and discuss each contribution to the effective potential for the approximate order parameters, and uncover new phenomena such as the paramagnetically-induced breaking of global $\\mathbb{Z}_3$ symmetry, and possible splitting of deconfinement and chiral transitions in a strong magnetic field.

  1. Broken symmetry approach to density functional calculation of magnetic anisotropy or zero field splittings for multinuclear complexes with antiferromagnetic coupling.

    Science.gov (United States)

    van Wüllen, Christoph

    2009-10-29

    Antiferromagnetic coupling in multinuclear transition metal complexes usually leads to electronic ground states that cannot be described by a single Slater determinant and that are therefore difficult to describe by Kohn-Sham density functional methods. Density functional calculations in such cases are usually converged to broken symmetry solutions which break spin and, in many cases, also spatial symmetry. While a procedure exists to extract isotropic Heisenberg (exchange) coupling constants from such calculations, no such approach is yet established for the calculation of magnetic anisotropy energies or zero field splitting parameters. This work proposes such a procedure. The broken symmetry solutions are not only used to extract the exchange couplings but also single-ion D tensors which are then used to construct a (phenomenological) spin Hamiltonian, from which the magnetic anisotropy and the zero-field energy levels can be computed. The procedure is demonstrated for a bi- and a trinuclear Mn(III) model compound.

  2. Chemical pressure effect in magnetic frustrated pyrochlore Nd2Pb2O7: A crystal-field analysis

    Science.gov (United States)

    Swarnakar, Debasish; Jana, Yatramohan; Alam, Jahangir; Nandi, Saikat

    2017-09-01

    Variation of chemical pressure at R-site due to substitution of nonmagnetic cation of varying size at the M-site makes a fine tuning between the crystal-field and molecular field to adopt exotic ground states in the frustrated magnetic R2M2O7 pyrochlore structures. Presence of larger cation at M-site increases the lattice parameter or nearest-neighbor bond distance between magnetic R-spins, and causes subtle changes to the local oxygen environment surrounding each R-ion, thereby reduces the chemical pressure at R-sites which leads to a dramatic change in the crystal-field and molecular field at R-site. To explore the effect of chemical pressure, the experimental results of powder magnetic susceptibility and isothermal magnetization of a geometrically frustrated compound, Nd2Pb2O7 containing largest cation, e.g. lead (Pb), at M4+-sites are simulated and analyzed employing a D3d crystal-field (CF) and anisotropic molecular field at R-sites in the self-consistent mean-field approach. The second-ordered axial parameter B20 and total CF splitting of the ground multiplet 4I9/2 of Nd3+-ions became the lowest among the isomorphic Nd-pyrochlore compounds, implying reduced effect of the crystal-field at Nd sites. Nd2Pb2O7 has strong [111] Ising anisotropy. Relative strength and values of the exchange tensor among nearest-neighbor Nd3+-spins in Nd2Pb2O7 and Nd2Zr2O7 result in a very close competition of anti-ferromagnetic and ferromagnetic interactions.

  3. 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...

  4. Non-linear exciton spin-splitting in single InAs/GaAs self-assembled quantum structures in ultrahigh magnetic fields

    OpenAIRE

    Babinski, A.; Ortner, G.; Raymond, S.; Potemski, M.; Bayer, M.; Hawrylak, P.; Forchel, A.; Wasilewski, Z.; Fafard,S.

    2005-01-01

    We report on the magnetic field dispersion of the exciton spin-splitting and diamagnetic shift in single InAs/GaAs quantum dots (QDs) and dot molecules (QDMs) up to $B$ = 28 T. Only for systems with strong geometric confinement, the dispersions can be well described by simple field dependencies, while for dots with weaker confinement considerable deviations are observed: most importantly, in the high field limit the spin-splitting shows a non-linear dependence on $B$, clearly indicating light...

  5. Near-field characterization of photonic crystal Y-splitters

    DEFF Research Database (Denmark)

    Volkov, V. S.; Bozhevolnyi, S. I.; Borel, Peter Ingo

    2005-01-01

    -1570 nm. The recorded intensity distribution exhibit highly wavelength (and polarization) dependent intensity variations along the propagation direction, especially around the fork and bend regions. By comparing the SNOM images recorded in and after the PC Y-splitter area, the features of light......A scanning near-field optical microscope (SNOM) is used to directly map the propagation of light in a specially designed 50/50 photonic crystal (PC) Y-splitter fabricated on silicon-on-insulator (SOI) wafers. SNOM images are obtained for TE- and TM-polarized light in the wavelength range 1425...

  6. Charge Penetration Effects in Rare-Earth Crystal Fields.

    Science.gov (United States)

    1982-06-01

    Interactions, 3. Three-Parameter Theory of Crystal Fields, Harry Diamond Laboratories HDL-TR-1673 (June 1975). 2R. M. Sternheimer , Phys. Rev., 84 (1951...R. M. Sternheimer , Phys. Rev., 84 (1951), 244. (3) R. E. Watson and A. J. Freeman, Phys. Rev., 135 (1964), A1209. (4) D. Sengupta and J. 0. Artman...A RARE-EARTH ION INTO THE CHARGE DI! THE RESULTS ARE CAST INTO A FORM REMINISCENT OF THE STERNHEIMER SHIELDING FA( A PRIME NM(R TO THE NTH POWER) TO

  7. Exact Analytical Solutions to the Two-Mode Mean-Field Model Describing Dynamics of a Split Bose-Einstein Condensate

    Institute of Scientific and Technical Information of China (English)

    WU Ying; YANG Xiao-Xue

    2002-01-01

    We present the analytical solutions to the two-mode mean-field model for a split Bose Einstein condensate.These explicit solutions completely determine the system's dynamics under the two-mode mean-field approximation for all possible initial conditions.

  8. Determination of the static zero-field splitting of Gd3+ complexes in solution from the shifts of the central magnetic fields of their EPR spectra.

    Science.gov (United States)

    Fries, Pascal H; Belorizky, Elie

    2012-06-04

    In principle, the Redfield theory of EPR spectra applies only to fast-rotating complexes with rather small static zero-field splitting (ZFS) terms. However, at sufficiently high frequencies, typically of 35 GHz and above, it predicts values of the central magnetic fields which are surprisingly accurate well beyond its expected applicability range. This remarkable feature is demonstrated by showing that the Redfield EPR spectrum crosses its baseline at the same point as its "exact" simulated counterpart. It is shown that the shift of the central magnetic field with respect to its limiting value in the absence of ZFS terms is often simply proportional to the square of the magnitude of the static ZFS term divided by the spectrometer frequency. This property is used to determine the magnitude of the static ZFS term independently of its fluctuation dynamics and of the presence of the transient ZFS term.

  9. Multidimensional stability analysis of the phase-field method for fracture with a general degradation function and energy split.

    Science.gov (United States)

    Arriaga, Miguel; Waisman, Haim

    2017-06-01

    A local physical stability criterion for multidimensional fracture problems modeled by the phase field method is developed and studied. Stability analysis provides a rigorous mathematical way to determine the onset of an unstable damage growth and fracture of the structure. In this work, stability is determined by examining the roots of a characteristic equation that arise when a linear perturbation technique is applied to the instantaneous partial differential equation system in a general viscoplastic material. It is shown that such analysis is not limited to a particular degradation function or energy split and could therefore be applied to a wide range of cases. Numerical results are presented to verify the theoretical predictions assuming quadratic and cubic degradation functions. Additionally we show that this stability criterion can be directly expanded to 2D with robust mesh-insensitive predictive capabilities with respect to crack nucleation and path. Several numerical examples are presented to verify these results.

  10. Organic single-crystal light-emitting field-effect transistors

    NARCIS (Netherlands)

    Hotta, Shu; Yamao, Takeshi; Bisri, Satria Zulkarnaen; Takenobu, Taishi; Iwasa, Yoshihiro

    2014-01-01

    Growth and characterisation of single crystals constitute a major field of materials science. In this feature article we overview the characteristics of organic single-crystal light-emitting field-effect transistors (OSCLEFETs). The contents include the single crystal growth of organic semiconductor

  11. Magnetic measurements and crystal field investigation on single crystals of Er(CF{sub 3}SO{sub 3}){sub 3}.9H{sub 2}O

    Energy Technology Data Exchange (ETDEWEB)

    Bisui, D. [Solid State Research Laboratory, Department of Physics, Burdwan University, Burdwan 713 104, West Bengal (India); Chattopadhyay, K.N. [Institute of Science Education, Burdwan University, Burdwan 713 104, West Bengal (India); Chakrabarti, P.K. [Solid State Research Laboratory, Department of Physics, Burdwan University, Burdwan 713 104, West Bengal (India)], E-mail: pabitra_c@hotmail.com

    2008-02-15

    Single crystals of erbium tri-fluoromethanesulfonate (ErTFMS) were prepared from the slow evaporation of the aqueous solution. The principal magnetic susceptibilities perpendicular to the c-axis of the hexagonal crystal was measured down to 13 K. Principal magnetic anisotropy was also measured from 300 K down to 80 K which provides principal susceptibility parallel to the c-axis down to 80 K. A very good theoretical simulation of the thermal variation of principal magnetic susceptibilities of ErTFMS has been obtained with a crystal field (CF) of C{sub 3h} site symmetry, in which J-mixed eigenvectors and intermediate coupling effects have been used. No ordering effects were noticed down to the lowest temperature (13 K) attained, indicating the inter-ionic interaction to be of predominantly dipolar type. The g-values are found to be g{sub parallel}=8.86 and g{sub perpendicular}=1.62, respectively. The Schottky anomaly in the electronic heat capacity at about 80 K has been computed from the Stark pattern. The thermal behavior of quadrupole splitting and hyperfine heat capacity were calculated from the CF analysis.

  12. Dynamically tuning the optical properties of Europium-doped sodium niobate nano-crystals through magnetic field

    Science.gov (United States)

    Xiao, Quanlan; Zhang, Yuanhao; Zhang, Junpei; Zhang, Han; Dong, Guoping; Han, Junbo; Qiu, Jianrong

    2016-11-01

    We have fabricated high quality NaNbO3:Eu3+ nano-crystals based on the Pechini sol-gel method and realized its magneto-optical effect under external pulsed magnetic field. Our results show that magnetic field can induce the suppression of luminescence, the splitting of peaks, and shifting of peak locations due to the expansion of electric dipole emission in Europium ions, and further demonstrate that the magnetic dipole emission plays an insignificant role in effect on the magnetic dipole emission for Eu3+:5 D 0 → 7 F 1, 5 D 0 → 7 F 3 transitions in NaNbO3:Eu3+ nano-crystals. These magnetic-optical interactions are attributed to the results of the Zeeman effect by high magnetic field that could result in the change of the symmetry of Eu3+ ions, and there is different sensitivity to changes of symmetry for Eu3+:5 D 0 → 7 F J (J = 1-4) transitions in NaNbO3 nano-crystals. This work might provide a viable magneto-optical approach in tuning the optical properties (luminescence intensity, peak location, profile, etc) of the rare-earth ions doped nano-particles.

  13. Magnetic Transitions in Iron Porphyrin Halides by Inelastic Neutron Scattering and Ab Initio Studies of Zero-Field Splittings.

    Science.gov (United States)

    Stavretis, Shelby E; Atanasov, Mihail; Podlesnyak, Andrey A; Hunter, Seth C; Neese, Frank; Xue, Zi-Ling

    2015-10-19

    Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H₂TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm⁻¹ for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm⁻¹, E = 0.1(2) cm⁻¹ and D = 13.4(6) cm⁻¹, E = 0.3(6) cm⁻¹ for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm⁻¹ for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X = F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the ⁶A₁ ground state. D was calculated from wave functions of the electronic multiplets spanned by the d⁵ configuration of Fe(III) along with spin–orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX₆³⁻ complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies e(λ)(X) (λ = σ, π) in the series from X = F to I. Analysis of this correlation using second-order perturbation theory expressions in terms of angular overlap parameters rationalizes the

  14. LO-TO splittings, effective charges and interactions in electro-optic meta-nitroaniline crystal as studied by polarized IR reflection and transmission spectra

    Science.gov (United States)

    Szostak, M. M.; Le Calvé, N.; Romain, F.; Pasquier, B.

    1994-10-01

    The polarized IR reflection spectra of the meta-nitroaniline ( m-NA) single crystal along the a, b and c crystallographic axes as well as the b and c polarized transmission spectra have been measured in the 100-400 cm -1 region. The LO-TO splitting values have been calculated from the reflection spectra by fitting them with the four parameter dielectric function. The dipole moment derivatives, relevant to dynamic effective charges, of the vibrations have also been calculated and used to check the applicability of the oriented gas model (OGM) to reflection spectra. The discrepancies from the OGM have been discussed in terms of vibronic couplings, weak hydrogen bondings (HB) and intramolecular charge transfer.

  15. Extremely strong temperature-dependent Davydow-splitting effects in the polarized IR spectra of the hydrogen bond: Pyrazole and quinolin-2(1H)-one crystals

    Science.gov (United States)

    Hachuła, Barbara; Flakus, Henryk T.; Tyl, Aleksandra; Polasz, Anna

    2014-04-01

    Polarized IR spectra were recorded in the spectral range of the νN-H and νN-D proton stretching vibration bands for the isotopically neat and isotopically diluted crystals of pyrazole (Pzl) and quinolin-2(1H)-one (2HQ). The spectra measured in the temperature range of 77-293 K have shown that temperature extremely strongly influenced the magnitude of the Davydow-splitting effects in the crystalline spectra. Two different competing vibrational Davydow-coupling mechanisms involving hydrogen bonds, i.e., the ‘tail-to-head' and the ‘side-to-side', were responsible for the generation of the temperature effects in the polarized spectra.

  16. Mode jumping of split-ring resonator metamaterials controlled by high-permittivity BST and incident electric fields

    Science.gov (United States)

    Fu, Xiaojian; Zeng, Xinxi; Cui, Tie Jun; Lan, Chuwen; Guo, Yunsheng; Zhang, Hao Chi; Zhang, Qian

    2016-08-01

    We investigate the resonant modes of split-ring resonator (SRR) metamaterials that contain high-permittivity BST block numerically and experimentally. We observe interesting mode-jumping phenomena from the BST-included SRR absorber structure as the excitation wave is incident perpendicularly to the SRR plane. Specifically, when the electric field is parallel to the SRR gap, the BST block in the gap will induce a mode jumping from the LC resonance to plasmonic resonance (horizontal electric-dipole mode), because the displacement current excited by the Mie resonance in the dielectric block acts as a current channel in the gap. When the electric field is perpendicular to the gap side, the plasmonic resonance mode (vertical electric-dipole mode) in SRR changes to two joint modes contributed simultaneously by the back layer, SRR and BST block, as a result of connected back layer and SRR layer by the displacement current in the BST dielectric block. Based on the mode jumping effect as well as temperature and electric-field dependent dielectric constant, the BST-included SRR metamaterials may have great potentials for the applications in electromagnetic switches and widely tunable metamaterial devices.

  17. Mode jumping of split-ring resonator metamaterials controlled by high-permittivity BST and incident electric fields.

    Science.gov (United States)

    Fu, Xiaojian; Zeng, Xinxi; Cui, Tie Jun; Lan, Chuwen; Guo, Yunsheng; Zhang, Hao Chi; Zhang, Qian

    2016-08-09

    We investigate the resonant modes of split-ring resonator (SRR) metamaterials that contain high-permittivity BST block numerically and experimentally. We observe interesting mode-jumping phenomena from the BST-included SRR absorber structure as the excitation wave is incident perpendicularly to the SRR plane. Specifically, when the electric field is parallel to the SRR gap, the BST block in the gap will induce a mode jumping from the LC resonance to plasmonic resonance (horizontal electric-dipole mode), because the displacement current excited by the Mie resonance in the dielectric block acts as a current channel in the gap. When the electric field is perpendicular to the gap side, the plasmonic resonance mode (vertical electric-dipole mode) in SRR changes to two joint modes contributed simultaneously by the back layer, SRR and BST block, as a result of connected back layer and SRR layer by the displacement current in the BST dielectric block. Based on the mode jumping effect as well as temperature and electric-field dependent dielectric constant, the BST-included SRR metamaterials may have great potentials for the applications in electromagnetic switches and widely tunable metamaterial devices.

  18. Systematic theoretical investigation of the zero-field splitting in Gd(III) complexes: Wave function and density functional approaches

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Shehryar, E-mail: sherkhan@fysik.su.se; Odelius, Michael, E-mail: odelius@fysik.su.se [Department of Physics, Stockholm University, AlbaNova University Center, S-106 91 Stockholm (Sweden); Kubica-Misztal, Aleksandra [Institute of Physics, Jagiellonian University, ul. Reymonta 4, PL-30-059 Krakow (Poland); Kruk, Danuta [Faculty of Mathematics and Computer Science, University of Warmia and Mazury in Olsztyn, Sloneczna 54, Olsztyn PL-10710 (Poland); Kowalewski, Jozef [Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm (Sweden)

    2015-01-21

    The zero-field splitting (ZFS) of the electronic ground state in paramagnetic ions is a sensitive probe of the variations in the electronic and molecular structure with an impact on fields ranging from fundamental physical chemistry to medical applications. A detailed analysis of the ZFS in a series of symmetric Gd(III) complexes is presented in order to establish the applicability and accuracy of computational methods using multiconfigurational complete-active-space self-consistent field wave functions and of density functional theory calculations. The various computational schemes are then applied to larger complexes Gd(III)DOTA(H{sub 2}O){sup −}, Gd(III)DTPA(H{sub 2}O){sup 2−}, and Gd(III)(H{sub 2}O){sub 8}{sup 3+} in order to analyze how the theoretical results compare to experimentally derived parameters. In contrast to approximations based on density functional theory, the multiconfigurational methods produce results for the ZFS of Gd(III) complexes on the correct order of magnitude.

  19. Mode jumping of split-ring resonator metamaterials controlled by high-permittivity BST and incident electric fields

    Science.gov (United States)

    Fu, Xiaojian; Zeng, Xinxi; Cui, Tie Jun; Lan, Chuwen; Guo, Yunsheng; Zhang, Hao Chi; Zhang, Qian

    2016-01-01

    We investigate the resonant modes of split-ring resonator (SRR) metamaterials that contain high-permittivity BST block numerically and experimentally. We observe interesting mode-jumping phenomena from the BST-included SRR absorber structure as the excitation wave is incident perpendicularly to the SRR plane. Specifically, when the electric field is parallel to the SRR gap, the BST block in the gap will induce a mode jumping from the LC resonance to plasmonic resonance (horizontal electric-dipole mode), because the displacement current excited by the Mie resonance in the dielectric block acts as a current channel in the gap. When the electric field is perpendicular to the gap side, the plasmonic resonance mode (vertical electric-dipole mode) in SRR changes to two joint modes contributed simultaneously by the back layer, SRR and BST block, as a result of connected back layer and SRR layer by the displacement current in the BST dielectric block. Based on the mode jumping effect as well as temperature and electric-field dependent dielectric constant, the BST-included SRR metamaterials may have great potentials for the applications in electromagnetic switches and widely tunable metamaterial devices. PMID:27502844

  20. Electron paramagnetic resonance study of alinement induced by magnetic fields in two smectic-A liquid crystals not exhibiting nematic phases

    Science.gov (United States)

    Fryburg, G. C.; Gelerinter, E.

    1972-01-01

    Using vanadyl acetylacetonate (VAAC) as a paramagnetic probe, the molecular ordering in two smectic-A liquid crystals that do not display nematic phases were studied. Reproducible alinement was attained by slow cooling throughout the isotropic smectic-A transition in dc magnetic fields of 1.1 and 2.15 teslas. The degree of order attained is small for a smectic-A liquid crystal. Measurements were made of the variation of the average hyperfine splitting of the alined samples as a function of orientation relative to the dc magnetic field of the spectrometer. This functional dependence is in agreement with the theoretical prediction except where the viscosity of the liquid crystal becomes large enough to slow the tumbling of the VAAC, as indicated by asymmetry in the end lines of the spectrum.

  1. Crystal field excitations of YbMn2Si2

    Science.gov (United States)

    Mole, R. A.; Hofmann, M.; Adroja, D. T.; Moze, O.; Campbell, S. J.

    2013-12-01

    The crystal field excitations of the rare earth intermetallic compound YbMn2Si2 have been measured by inelastic neutron scattering over the temperature range 2.5-50 K. The YbMn2Si2 spectra exhibit three low energy excitations (~3-7 meV) in the antiferromagnetic AFil region above the magnetic phase transition at TN2 = 30(5) K. The crystal field parameters have been determined for YbMn2Si2 in the antiferromagnetic AFil region. A further two inelastic excitations (~9 meV, 17 meV) are observed below TN2=30(5) K, the temperature at which the high temperature antiferromagnetic structure is reported to exhibit doubling of the magnetic cell. Energy level diagrams have been determined for Yb3+ ions in the different sites above (single site) and below the magnetic transition temperature (two sites). The excitation energies for both sites are shown to be temperature independent with the temperature dependences of the transition intensities for the two sites described well by a simple Boltzmann model. The spectra below TN2 cannot be described fully in terms of molecular field models based on either a single Yb3+ site or two Yb3+ sites. This indicates that the magnetic behaviour of YbMn2Si2 is more complicated than previously considered. The inability to account fully for excitations below the magnetic phase transition may be due to an, as yet, unresolved structural transition associated with the magnetic transition.

  2. Hysteresis behaviors of the crystal field diluted general spin-S Ising model

    Science.gov (United States)

    Akıncı, Ümit

    2017-10-01

    Hysteresis characteristics of the crystal field diluted general Spin-S (S > 1) Blume-Capel model have been studied within the effective field approximation. Particular emphasis has been paid on the large negative valued crystal field and low temperature region and it has been demonstrated for this region that, rising dilution of the crystal field results in decreasing number of windowed hysteresis loops. The evolution of the multiple hysteresis loop with the dilution of the crystal field has been investigated and physical mechanism behind this evolution has been given.

  3. Autler- Townes Splitting in Photoelectron Spectrum of Three-Level Li2 Molecule in Ultrashort Pulse Laser Fields

    Institute of Scientific and Technical Information of China (English)

    HU Wen-Hui; YUAN Kai-Jun; HAN Yong-Chang; Shu Chuang-Cun; CONG Shu-Lin

    2007-01-01

    The Autler-Townes (AT) splitting in femtosecond photoelectron spectrum of three-level Lii molecules is theoretically investigated using time-dependent quantum wave packet method. With proper femtosecond laser pulses, three peaks of the AT splitting can be observed in the photoelectron spectrum. The AT splitting stems from rapid Rabi oscillation caused by intense ultrashort laser pluses. The effects of laser parameters on the molecular ionization dynamics are also discussed.

  4. Direct observation of electronic and nuclear ground state splitting in external magnetic field by inelastic neutron scattering on oxidized ferrocene and ferrocene containing polymers

    Directory of Open Access Journals (Sweden)

    Appel Markus

    2015-01-01

    Full Text Available The quantum mechanical splitting of states by interaction of a magnetic moment with an external magnetic field is well known, e.g., as Zeeman effect in optical transitions, and is also often seen in magnetic neutron scattering. We report excitations observed in inelastic neutron spectroscopy on the redox-responsive polymer poly(vinylferrocene. They are interpreted as splitting of the electronic ground state in the organometallic ferrocene units attached to the polymer chain where a magnetic moment is created by oxidation. In a second experiment using high resolution neutron backscattering spectroscopy we observe the hyperfine splitting, i.e., interaction of nuclear magnetic moments with external magnetic fields leading to sub-μeV excitations observable in incoherent neutron spin-flip scattering on hydrogen and vanadium nuclei.

  5. The Effects of a Magnetic Field on the Crystallization of a Fluorozirconate Glass

    Science.gov (United States)

    Tucker, Dennis S.; Lapointe, Michael R.; Jia, Zhiyong

    2006-01-01

    An axial magnetic field of 0.1T was applied to ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results and tested by measuring the magnetic susceptibilities of the glass and crystal.

  6. Crystal field effects on interionic distance in cubic MgO crystal doped with Fe{sup 2+} ions

    Energy Technology Data Exchange (ETDEWEB)

    Ivascu, S.; Gruia, A.S. [Faculty of Physics, West University of Timisoara, Bd. V. Parvan 4, 300223-Timisoara (Romania); Avram, N.M., E-mail: avram@physics.uvt.ro [Faculty of Physics, West University of Timisoara, Bd. V. Parvan 4, 300223-Timisoara (Romania); Academy of Romanian Scientists, Independentei 54, 050094-Bucharest (Romania)

    2014-10-01

    The exchange charge model of crystal field was applied to determine the dependence of the crystal field strength 10Dq on interionic distances R between the Fe{sup 2+} impurity ion and O{sup 2−} ligands in cubic MgO:Fe{sup 2+}. The obtained results were extrapolated by the power law and was shown that 10Dq depends on R as 1/R{sup n}, with n=6.3486. The deviations of these values from the value n=5 (predicted by the simple point charge model of crystal field) is explained by the covalent and exchange effects between impurity ion and ligands; the contribution of these effects into the total crystal field strength was considered separately. The 10Dq functions obtained as a result of our calculations were used for estimations of the electron–vibrational constants, Huang–Rhys parameters, and Jahn–Teller stabilization energy, and compared with available literature data.

  7. Crystal field effects on interionic distance in cubic MgO crystal doped with Fe2+ ions

    Science.gov (United States)

    Ivascu, S.; Gruia, A. S.; Avram, N. M.

    2014-10-01

    The exchange charge model of crystal field was applied to determine the dependence of the crystal field strength 10Dq on interionic distances R between the Fe2+ impurity ion and O2- ligands in cubic MgO:Fe2+. The obtained results were extrapolated by the power law and was shown that 10Dq depends on R as 1/R, with n=6.3486. The deviations of these values from the value n=5 (predicted by the simple point charge model of crystal field) is explained by the covalent and exchange effects between impurity ion and ligands; the contribution of these effects into the total crystal field strength was considered separately. The 10Dq functions obtained as a result of our calculations were used for estimations of the electron-vibrational constants, Huang-Rhys parameters, and Jahn-Teller stabilization energy, and compared with available literature data.

  8. Experimental investigation and crystal-field modeling of Er{sup 3+} energy levels in GSGG crystal

    Energy Technology Data Exchange (ETDEWEB)

    Gao, J.Y., E-mail: jygao1985@sina.com [Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031 (China); Sun, D.L.; Zhang, Q.L. [Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031 (China); Wang, X.F. [Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100049 (China); Liu, W.P.; Luo, J.Q.; Sun, G.H.; Yin, S.T. [Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031 (China)

    2016-06-25

    The Er{sup 3+}-doped Gd{sub 3}Sc{sub 2}Ga{sub 3}O{sub 12} (Er{sup 3+}:GSGG) single crystal, a excellent medium of the mid-infrared and anti-radiation solid state laser pumped by laser diode, was grown by Czochralski method successfully. The absorption spectra were measured and analyzed in a wider spectral wavelength range of 350–1700 nm at different temperatures of 7.6, 77, 200 and 300 K. The free-ions and crystal-field parameters were fitted to the experimental energy levels with the root mean square deviation of 9.86 cm{sup −1}. According to the crystal-field calculations, 124 degenerate energy levels of Er{sup 3+} in GSGG host crystals were assigned. The fitting results of free-ions and crystal-field parameters were compared with those already reported of Er{sup 3+}:YSGG. The results indicated that the free-ions parameters for Er{sup 3+} in GSGG host are similar to those in YSGG host crystals, and the crystal-field interaction of GSGG is weaker than that of YSGG, which may result in the better laser characterization of Er{sup 3+}:GSGG crystal. - Highlights: • The efficient diode-end-pumped laser crystal Er:GSGG has been grown successfully. • The absorption spectra of Er:GSGG have been measured in range of 350–1700 nm. • The fitting result is very well for the root mean square deviation is 9.86 cm{sup −1}. • The 124 levels of Er:GSGG have been assigned from the crystal-field calculations.

  9. [Tablet splitting].

    Science.gov (United States)

    Quinzler, R; Haefeli, W E

    2006-06-01

    The splitting of scored tablets provides many advantages. One benefit is to achieve dose flexibility to account for the huge interindividual differences in dose requirements for instance in paediatric and geriatric patients, which are often not covered by the available strengths in the market. Moreover, large-sized tablets can easier be swallowed if broken before swallowing and medication costs can often be reduced by splitting brands with higher strength. But not all tablets, mostly unscored tablets, are suitable for splitting. Splitting of extended release formulations can result in an overdose by uncontrolled release of the active component and degradation of the compound can occur if an enteric coating is destroyed by the splitting process. Whether tablets are suitable for splitting depends on the properties of the active component (e.g. light sensitivity), the galenics, the shape of the tablet, and the shape of the scoreline. Moreover, not all patients are informed, able, or willing to split tablets and the majority of the elderly population is not capable to break tablets. When split tablets are prescribed it is therefore important to view the shape of the tablet, to assess the patients ability and willingness to break tablets, to properly inform the patient about the appropriate way of splitting, and if necessary to suggest (and instruct) the use of a tablet splitting device.

  10. Spin-1 Blume-Capel model with longitudinal random crystal and transverse magnetic fields:A mean-field approach

    Institute of Scientific and Technical Information of China (English)

    Erhan Albayrak

    2013-01-01

    The spin-1 Blume-Capel model with transverse Ω and longitudinal external magnetic fields h,in addition to a longitudinal random crystal field D,is studied in the mean-field approximation.It is assumed that the crystal field is either turned on with probability p or turned off with probability 1-p on the sites of a square lattice.Phase diagrams are then calculated on the reduced temperature crystal field planes for given values of γ =-Ω/J and p at zero h.Thus,the effect of changing γ and p are illustrated on the phase diagrams in great detail and interesting results are observed.

  11. Hybrid excitations due to crystal field, spin-orbit coupling, and spin waves in LiFePO4

    Science.gov (United States)

    Yiu, Yuen; Le, Manh Duc; Toft-Peterson, Rasmus; Ehlers, Georg; McQueeney, Robert J.; Vaknin, David

    2017-03-01

    We report on the spin waves and crystal field excitations in single crystal LiFePO4 by inelastic neutron scattering over a wide range of temperatures, below and above the antiferromagnetic transition of this system. In particular, we find extra excitations below TN=50 K that are nearly dispersionless and are most intense around magnetic zone centers. We show that these excitations correspond to transitions between thermally occupied excited states of Fe2 + due to splitting of the S =2 levels that arise from the crystal field and spin-orbit interactions. These excitations are further amplified by the highly distorted nature of the oxygen octahedron surrounding the iron atoms. Above TN, magnetic fluctuations are observed up to at least 720 K, with an additional inelastic excitation around 4 meV, which we attribute to single-ion effects, as its intensity weakens slightly at 720 K compared to 100 K, which is consistent with the calculated cross sections using a single-ion model. Our theoretical analysis, using the MF-RPA model, provides both detailed spectra of the Fe d shell and estimates of the average ordered magnetic moment and TN. By applying the MF-RPA model to a number of existing spin-wave results from other Li M PO4 (M =Mn , Co, and Ni), we are able to obtain reasonable predictions for the moment sizes and transition temperatures.

  12. Reductive renormalization of the phase-field crystal equation.

    Science.gov (United States)

    Oono, Y; Shiwa, Y

    2012-12-01

    It has been known for some time that singular perturbation and reductive perturbation can be unified from the renormalization-group theoretical point of view: Reductive extraction of space-time global behavior is the essence of singular perturbation methods. Reductive renormalization was proposed to make this unification practically accessible; actually, this reductive perturbation is far simpler than most reduction methods, such as the rather standard scaling expansion. However, a rather cryptic exposition of the method seems to have been the cause of some trouble. Here, an explicit demonstration of the consistency of the reductive renormalization-group procedure is given for partial differentiation equations (of a certain type, including time-evolution semigroup type equations). Then, the procedure is applied to the reduction of a phase-field crystal equation to illustrate the streamlined reduction method. We conjecture that if the original system is structurally stable, the reductive renormalization-group result and that of the original equation are diffeomorphic.

  13. Raman spectrum of plutonium dioxide: Vibrational and crystal field modes

    Science.gov (United States)

    Naji, M.; Magnani, N.; Bonales, L. J.; Mastromarino, S.; Colle, J.-Y.; Cobos, J.; Manara, D.

    2017-03-01

    The Raman spectrum of plutonium dioxide is studied both experimentally and theoretically. Particular attention has been devoted to the identification of high-energy modes at 2110 and 2620 c m-1 , whose attribution has so far been controversial. The temperature dependence of both modes suggests an electronic origin for them. Original crystal field (CF) calculations reported in this work show that these two modes can be respectively assigned to the Γ1→Γ5 and Γ1→Γ3 CF transitions within the I54 manifold. These two modes, together with the only vibrational line foreseen by the group theory for the F m -3 m Pu O2 symmetry—the T2 gPu -O stretching mode observed at 478 c m-1 —can thus be used as a Raman fingerprint of fcc plutonium dioxide.

  14. Microwave-assisted self-doping of TiO2 photonic crystals for efficient photoelectrochemical water splitting

    KAUST Repository

    Zhang, Zhonghai

    2014-01-08

    In this article, we report that the combination of microwave heating and ethylene glycol, a mild reducing agent, can induce Ti3+ self-doping in TiO2. A hierarchical TiO2 nanotube array with the top layer serving as TiO2 photonic crystals (TiO2 NTPCs) was selected as the base photoelectrode. The self-doped TiO2 NTPCs demonstrated a 10-fold increase in visible-light photocurrent density compared to the nondoped one, and the optimized saturation photocurrent density under simulated AM 1.5G illumination was identified to be 2.5 mA cm-2 at 1.23 V versus reversible hydrogen electrode, which is comparable to the highest values ever reported for TiO2-based photoelectrodes. The significant enhancement of photoelectrochemical performance can be ascribed to the rational coupling of morphological and electronic features of the self-doped TiO 2 NTPCs: (1) the periodically morphological structure of the photonic crystal layer traps broadband visible light, (2) the electronic interband state induced from self-doping of Ti3+ can be excited in the visible-light region, and (3) the captured light by the photonic crystal layer is absorbed by the self-doped interbands. © 2013 American Chemical Society.

  15. The crystal structure of the Split End protein SHARP adds a new layer of complexity to proteins containing RNA recognition motifs.

    Science.gov (United States)

    Arieti, Fabiana; Gabus, Caroline; Tambalo, Margherita; Huet, Tiphaine; Round, Adam; Thore, Stéphane

    2014-06-01

    The Split Ends (SPEN) protein was originally discovered in Drosophila in the late 1990s. Since then, homologous proteins have been identified in eukaryotic species ranging from plants to humans. Every family member contains three predicted RNA recognition motifs (RRMs) in the N-terminal region of the protein. We have determined the crystal structure of the region of the human SPEN homolog that contains these RRMs-the SMRT/HDAC1 Associated Repressor Protein (SHARP), at 2.0 Å resolution. SHARP is a co-regulator of the nuclear receptors. We demonstrate that two of the three RRMs, namely RRM3 and RRM4, interact via a highly conserved interface. Furthermore, we show that the RRM3-RRM4 block is the main platform mediating the stable association with the H12-H13 substructure found in the steroid receptor RNA activator (SRA), a long, non-coding RNA previously shown to play a crucial role in nuclear receptor transcriptional regulation. We determine that SHARP association with SRA relies on both single- and double-stranded RNA sequences. The crystal structure of the SHARP-RRM fragment, together with the associated RNA-binding studies, extend the repertoire of nucleic acid binding properties of RRM domains suggesting a new hypothesis for a better understanding of SPEN protein functions.

  16. Using frequency detuning to improve the sensitivity of electric field measurements via electromagnetically induced transparency and Autler-Townes splitting in Rydberg atoms

    Science.gov (United States)

    Simons, Matt T.; Gordon, Joshua A.; Holloway, Christopher L.; Anderson, David A.; Miller, Stephanie A.; Raithel, Georg

    2016-04-01

    In this work, we demonstrate an approach for improved sensitivity in weak radio frequency (RF) electric-field strength measurements using Rydberg electromagnetically induced transparency (EIT) in an atomic vapor. This is accomplished by varying the RF frequency around a resonant atomic transition and extrapolating the weak on-resonant field strength from the resulting off-resonant Autler-Townes (AT) splittings. This measurement remains directly traceable to SI compared to previous techniques, precluding any knowledge of experimental parameters such as optical beam powers as is the case when using the curvature of the EIT line shape to measure weak fields. We use this approach to measure weak RF fields at 182 GHz and 208 GHz demonstrating improvement greater than a factor of 2 in the measurement sensitivity compared to on-resonant AT splitting RF electric field measurements.

  17. Crystal-field analysis of Eu sup 3 sup + in Lu sub 2 O sub 3

    CERN Document Server

    Karbowiak, M; Hoelsae, J

    2003-01-01

    Low temperature (7 K) absorption spectra of polycrystalline sintered ceramic Lu sub 2 O sub 3 :Eu sup 3 sup + were recorded between 3950 and 50000 cm sup - sup 1. There are two different intrinsic Eu sup 3 sup + sites, C sub 2 and S sub 6 (C sub 3 sub i), in this host. A total of 105 crystal-field (CF) energy levels were assigned and fitted to a semiempirical Hamiltonian representing the combined free-ion (FI) and CF interactions for a 4f sup 6 ion in the C sub 2 symmetry site. 10 FI and 14 CF parameters were varied simultaneously in the least square adjustments yielding an rms deviation between the calculated and experimental levels of 15 cm sup - sup 1. The CF strength parameter, S, obtained from calculated B sub q sup k parameters is larger for Lu sub 2 O sub 3 when compared to the Y sub 2 O sub 3 host, which is in accordance with the smaller ionic radius of the Lu sup 3 sup + ion. The CF splittings of the sup 7 F sub 1 and sup 5 D sub 1 levels were also determined experimentally for the Eu sup 3 sup + ion...

  18. The Strength of PIN-PMN-PT Single Crystals under Bending with a Longitudinal Electric Field

    Science.gov (United States)

    2011-04-06

    The strength of PIN– PMN – PT single crystals under bending with a longitudinal electric field This article has been downloaded from IOPscience. Please...COVERED 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE The Strength Of PIN- PMN - PT Single Crystals Under Bending With A Longitudinal Electric Field... PMN ? PT ) single crystals was measured using a four point bending apparatus with a longitudinal electric field applied to the bar during bending. The

  19. Efficient split field FDTD analysis of third-order nonlinear materials in two-dimensionally periodic media

    Science.gov (United States)

    Francés, Jorge; Bleda, Sergio; Bej, Subhajit; Tervo, Jani; Navarro-Fuster, Víctor; Fenoll, Sandra; Martínez-Gaurdiola, Francisco J.; Neipp, Cristian

    2016-04-01

    In this work the split-field finite-difference time-domain method (SF-FDTD) has been extended for the analysis of two-dimensionally periodic structures with third-order nonlinear media. The accuracy of the method is verified by comparisons with the nonlinear Fourier Modal Method (FMM). Once the formalism has been validated, examples of one- and two-dimensional nonlinear gratings are analysed. Regarding the 2D case, the shifting in resonant waveguides is corroborated. Here, not only the scalar Kerr effect is considered, the tensorial nature of the third-order nonlinear susceptibility is also included. The consideration of nonlinear materials in this kind of devices permits to design tunable devices such as variable band filters. However, the third-order nonlinear susceptibility is usually small and high intensities are needed in order to trigger the nonlinear effect. Here, a one-dimensional CBG is analysed in both linear and nonlinear regime and the shifting of the resonance peaks in both TE and TM are achieved numerically. The application of a numerical method based on the finite- difference time-domain method permits to analyse this issue from the time domain, thus bistability curves are also computed by means of the numerical method. These curves show how the nonlinear effect modifies the properties of the structure as a function of variable input pump field. When taking the nonlinear behaviour into account, the estimation of the electric field components becomes more challenging. In this paper, we present a set of acceleration strategies based on parallel software and hardware solutions.

  20. An Overview of Hardware for Protein Crystallization in a Magnetic Field

    Directory of Open Access Journals (Sweden)

    Er-Kai Yan

    2016-11-01

    Full Text Available Protein crystallization under a magnetic field is an interesting research topic because a magnetic field may provide a special environment to acquire improved quality protein crystals. Because high-quality protein crystals are very useful in high-resolution structure determination using diffraction techniques (X-ray, neutron, and electron diffraction, research using magnetic fields in protein crystallization has attracted substantial interest; some studies have been performed in the past two decades. In this research field, the hardware is especially essential for successful studies because the environment is special and the design and utilization of the research apparatus in such an environment requires special considerations related to the magnetic field. This paper reviews the hardware for protein crystallization (including the magnet systems and the apparatus designed for use in a magnetic field and progress in this area. Future prospects in this field will also be discussed.

  1. Phase-field modeling on morphological landscape of isotactic polystyrene single crystals.

    Science.gov (United States)

    Xu, Haijun; Matkar, Rushikesh; Kyu, Thein

    2005-07-01

    Spatio-temporal growth of isotactic polystyrene single crystals during isothermal crystallization has been investigated theoretically based on the phase field model by solving temporal evolution of a nonconserved phase order parameter coupled with a heat conduction equation. In the description of the total free energy, an asymmetric double-well local free energy density has been adopted to represent the metastable melt and the stable solid crystal. Unlike the small molecule systems, polymer crystallization rarely reaches thermodynamic equilibrium; most polymer crystals are kinetically stabilized in some metastable states. To capture various metastable polymer crystals, the phase field crystal order parameter at the solidification potential has been treated to be supercooling dependent such that it can assume an intermediate value between zero (melt) and unity (perfect crystal), reflecting imperfect polycrystalline nature of polymer crystals. Two-dimensional simulations exhibit various single crystal morphologies of isotactic polystyrene crystals such as faceted hexagonal patterns transforming to nonfaceted snowflakes with increasing supercooling. Of particular interest is that heat liberation from the crystallizing front influences the curvature of the crystal-melt interface, leading to directional growth of lamellar tips and side branches. The landscape of these morphological textures has been established as a function of anisotropy of surface energy and supercooling. With increasing supercooling and decreasing anisotropy, the hexagonal single crystal transforms to the dense lamellar branching morphology in conformity with the experimental findings.

  2. Increasing the effective aperture of a detector and enlarging the receiving field of view in a 3D imaging lidar system through hexagonal prism beam splitting.

    Science.gov (United States)

    Lee, Xiaobao; Wang, Xiaoyi; Cui, Tianxiang; Wang, Chunhui; Li, Yunxi; Li, Hailong; Wang, Qi

    2016-07-11

    The detector in a highly accurate and high-definition scanning 3D imaging lidar system requires high frequency bandwidth and sufficient photosensitive area. To solve the problem of small photosensitive area of an existing indium gallium arsenide detector with a certain frequency bandwidth, this study proposes a method for increasing the receiving field of view (FOV) and enlarging the effective photosensitive aperture of such detector through hexagonal prism beam splitting. The principle and construction of hexagonal prism beam splitting is also discussed in this research. Accordingly, a receiving optical system with two hexagonal prisms is provided and the splitting beam effect of the simulation experiment is analyzed. Using this novel method, the receiving optical system's FOV can be improved effectively up to ±5°, and the effective photosensitive aperture of the detector is increased from 0.5 mm to 1.5 mm.

  3. Description of hard-sphere crystals and crystal-fluid interfaces: a comparison between density functional approaches and a phase-field crystal model.

    Science.gov (United States)

    Oettel, M; Dorosz, S; Berghoff, M; Nestler, B; Schilling, T

    2012-08-01

    In materials science the phase-field crystal approach has become popular to model crystallization processes. Phase-field crystal models are in essence Landau-Ginzburg-type models, which should be derivable from the underlying microscopic description of the system in question. We present a study on classical density functional theory in three stages of approximation leading to a specific phase-field crystal model, and we discuss the limits of applicability of the models that result from these approximations. As a test system we have chosen the three-dimensional suspension of monodisperse hard spheres. The levels of density functional theory that we discuss are fundamental measure theory, a second-order Taylor expansion thereof, and a minimal phase-field crystal model. We have computed coexistence densities, vacancy concentrations in the crystalline phase, interfacial tensions, and interfacial order parameter profiles, and we compare these quantities to simulation results. We also suggest a procedure to fit the free parameters of the phase-field crystal model. Thereby it turns out that the order parameter of the phase-field crystal model is more consistent with a smeared density field (shifted and rescaled) than with the shifted and rescaled density itself. In brief, we conclude that fundamental measure theory is very accurate and can serve as a benchmark for the other theories. Taylor expansion strongly affects free energies, surface tensions, and vacancy concentrations. Furthermore it is phenomenologically misleading to interpret the phase-field crystal model as stemming directly from Taylor-expanded density functional theory.

  4. Multireference ab initio studies of zero-field splitting and magnetic circular dichroism spectra of tetrahedral Co(II) complexes.

    Science.gov (United States)

    Sundararajan, Mahesh; Ganyushin, Dmitry; Ye, Shengfa; Neese, Frank

    2009-08-14

    A newly developed multireference (MR) ab initio method for the calculation of magnetic circular dichroism (MCD) spectra was calibrated through the calculation of the ground- and excited state properties of seven high-spin (S = 3/2) Co(II) complexes. The MCD spectra were computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. For the complexes studied in this work, we found that the SOC is more important than the SSC for determining the ground state zero field splitting (ZFS). Our computed ZFS parameter D for the [Co(PPh(3))(2)Cl(2)] model complex is -17.6 cm(-1), which is reasonably close to the experimental value of -14.8 cm(-1). Generally, the computed absorption and MCD spectra are in fair agreement with experiment for all investigated complexes. Thus, reliable electronic structure and spectroscopic predictions for medium sized transition metal complexes are feasible on the basis of this methodology. This characterizes the presented method as a promising tool for MCD spectra interpretations of transition metal complexes in a variety of areas of chemistry and biology.

  5. The resolution of the identity approximation for calculations of spin-spin contribution to zero-field splitting parameters

    Science.gov (United States)

    Ganyushin, Dmitry; Gilka, Natalie; Taylor, Peter R.; Marian, Christel M.; Neese, Frank

    2010-04-01

    In this work, the resolution of the identity (RI) approximation is developed for the calculation of the electron-electron spin-spin coupling (SSC) interaction that is a central component of the zero-field splitting (ZFS) term in the effective spin Hamiltonian. The approximated integrals are then used in large-scale multireference configuration interaction treatments of the SSC interaction. The SSC contribution to the ZFS is treated using the Breit-Pauli spin-spin Hamiltonian in conjunction with first-order perturbation theory. Test calculations on a set of diatomic molecules reveal that the error of the RI approximation does not exceed 0.01 cm-1 even if standard auxiliary basis sets are used. This error of less than 1% is considered to be negligible compared to the presently achievable accuracy of the SSC calculations relative to experimental data. The present development allows the correlated ab initio calculation of ZFS parameters of larger systems such as linear polyenes and linear polyacenes. The basis set convergence of the calculated ZFS values was investigated, and the effect of electronic correlation on the calculated ZFS parameters is discussed.

  6. Magnetic field effects on the Rabi splitting and radiative decay rates of the exciton-polariton states in a semiconductor microcavity

    Science.gov (United States)

    Fenniche, H.; Jaziri, S.; Bennaceur, R.

    1998-12-01

    We study theoretically a particular type of semiconductor microcavity formed by a quantum well embedded inside it and the distributed Bragg reflectors presenting a gradual structure. We apply to this structure a static magnetic field along the growth direction. In the strong coupling regime between the confined exciton and cavity modes, we evaluate the polariton Rabi splitting corresponding to the two lowest lying exciton states: HH1-CB1 and HH2-CB2 as a function of the applied magnetic field. In high magnetic field and for distinct reflectivities, we find that the Rabi splitting magnitude of the HH2-CB2 exciton is close to the fundamental one (HH1-CB1). In the presence of the magnetic field, the polariton Rabi splitting can be obtained even in low reflectivity. The dispersion polariton radiative decay rates related to the two lowest lying exciton states: HH1-CB1 and HH2-CB2 are calculated for different magnetic field values. At k //=0 and in the weak coupling regime, the polariton radiative decay rates are evaluated for both the HH1-CB1 and HH2-CB2 excitons. We show that for the fundamental excitonic state, the magnetic field value which determines the transition from the weak to the strong coupling regime is different from the HH2-CB2 exciton state.

  7. Crystal Fields in Dilute Rare-Earth Metals Obtained from Magnetization Measurements on Dilute Rare-Earth Alloys

    DEFF Research Database (Denmark)

    Touborg, P.; Høg, J.

    1974-01-01

    Crystal field parameters of Tb, Dy, and Er in Sc, Y, and Lu are summarized. These parameters are obtained from magnetization measurements on dilute single crystals, and successfully checked by a number of different methods. The crystal field parameters vary unpredictably with the rare-earth solute....... B40, B60, and B66 are similar in Y and Lu. Crystal field parameters for the pure metals Tb, Dy, and Er are estimated from the crystal fields in Y and Lu....

  8. SOLIDIFICATION OF NICKEL-BASED SINGLE CRYSTAL SUPERALLOY BY ELECTRIC FIELD

    Institute of Scientific and Technical Information of China (English)

    Y.S. Yang; X.H. Feng; G.F. Cheng; Y.J. Li; Z.Q. Hu

    2005-01-01

    The crystal growth of a nickel-based single crystal superalloy DD3 was researched via controlled directional solidification under the action of a DC electric field. The cellular or dendrite spacing of the single crystal superalloy is refined and microsegregation of alloying elements Al,Ti, Mo and W, is reduced by the electric field. The electric field decreases the interface stability and reduces the critical growth rate of the cellular-dendritic translation because of Thomson effect and Joule heating. The precipitation of the γ' phase is more uniform and the size of the γ'phase is smaller with the electric field than that without the electric field.

  9. Estimation of the Birefringence Change in Crystals Induced by Gravitation Field

    OpenAIRE

    Vlokh R.; Kostyrko M.

    2007-01-01

    The effect of gravitation field of spherically symmetric mass on the birefringent properties of crystals has been analysed. It has been shown that the gravitation field with spherical symmetry can lead to a change of birefringence in anisotropic media.

  10. Three-dimensional study of planar optical antennas made of split-ring architecture outperforming dipole antennas for increased field localization.

    Science.gov (United States)

    Kilic, Veli Tayfun; Erturk, Vakur B; Demir, Hilmi Volkan

    2012-01-15

    Optical antennas are of fundamental importance for the strongly localizing field beyond the diffraction limit. We report that planar optical antennas made of split-ring architecture are numerically found in three-dimensional simulations to outperform dipole antennas for the enhancement of localized field intensity inside their gap regions. The computational results (finite-difference time-domain) indicate that the resulting field localization, which is of the order of many thousandfold, in the case of the split-ring resonators is at least 2 times stronger than the one in the dipole antennas resonant at the same operating wavelength, while the two antenna types feature the same gap size and tip sharpness.

  11. Single-crystal organic field-effect transistors based on dibenzo-tetrathiafulvalene

    NARCIS (Netherlands)

    Mas-Torrent, M.; Hadley, P.; Bromley, S.T.; Crivillers, N.; Veciana, J.; Rovira, C.

    2004-01-01

    We report on the fabrication and characterization of field-effect transistors based on single crystals of the organic semiconductor dibenzo-tetrathiafulvalene (DB-TTF). We demonstrate that it is possible to prepare very-good-quality DB-TTF crystals from solution. These devices show high field-effect

  12. Method to map individual electromagnetic field components inside a photonic crystal

    NARCIS (Netherlands)

    Denis, T.; Reijnders, B.; Lee, J.H.H.; van der Slot, Petrus J.M.; Vos, Willem L.; Boller, Klaus J.

    2012-01-01

    We present a method to map the absolute electromagnetic field strength inside photonic crystals. We apply the method to map the dominant electric field component Ez of a two-dimensional photonic crystal slab at microwave frequencies. The slab is placed between two mirrors to select Bloch standing

  13. Static magnetic susceptibility, crystal field and exchange interactions in rare earth titanate pyrochlores

    NARCIS (Netherlands)

    Malkin, B. Z.; Lummen, T. T. A.; van Loosdrecht, P. H. M.; Dhalenne, G.; Zakirov, A. R.

    2010-01-01

    The experimental temperature dependence (T = 2-300 K) of single crystal bulk and site susceptibilities of rare earth titanate pyrochlores R2Ti2O7 (R = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) is analyzed in the framework of crystal field theory and a mean field approximation. Analytical expressions for the s

  14. Crystal fields at light rare-earth ions in Y and Lu

    DEFF Research Database (Denmark)

    Touborg, P.; Nevald, Rolf; Johansson, Torben

    1978-01-01

    Crystal-field parameters have been deduced for the light rare-earth solutes Ce, Pr, and Nd in Y or Lu hosts from measurements of the paramagnetic susceptibilities. In the analysis all multiplets in the lowest LS term were included. For a given host, crystal-field parameters divided by Stevens fac...

  15. Effect of axial magnetic field on the shape of copper ribbon crystal grown by Czochralski method

    OpenAIRE

    Shen, Zhe; Zhong, Yunbo; Dong, Licheng; FAN, Lijun; Wang, Huai; Li, Chuanjun; Ren, Weili; Lei, Zuosheng; Ren, Zhongming

    2015-01-01

    International audience; During the process of growing ribbon crystal by Czochralski method, Turbulent convection in copper melt was effectively suppressed by applying an axial magnetic field (magnetic induction B≤57mT). The changes of thermal fluctuation and flow field were measured and modeled. With the magnetic field increased gradually (from 0 to 57mT), the shape of ribbon crystal became regularly wider. We concluded that the axial magnetic field could promote to form a suitable temperatur...

  16. Phonon and crystal field excitations in geometrically frustrated rare earth titanates

    Science.gov (United States)

    Lummen, T. T. A.; Handayani, I. P.; Donker, M. C.; Fausti, D.; Dhalenne, G.; Berthet, P.; Revcolevschi, A.; van Loosdrecht, P. H. M.

    2008-06-01

    The phonon and crystal field excitations in several rare earth titanate pyrochlores are investigated. Magnetic measurements on single crystals of Gd2Ti2O7 , Tb2Ti2O7 , Dy2Ti2O7 , and Ho2Ti2O7 are used for characterization, while Raman spectroscopy and terahertz time domain spectroscopy are employed to probe the excitations in the materials. The lattice excitations are found to be analogous across the compounds over the whole temperature range investigated (295-4 K). The resulting full phononic characterization of the R2Ti2O7 pyrochlore structure is then used to identify crystal field excitations observed in the materials. Several crystal field excitations have been observed in Tb2Ti2O7 in Raman spectroscopy, among which all of the previously reported excitations. The presence of additional crystal field excitations, however, suggests the presence of two inequivalent Tb3+ sites in the low-temperature structure. Furthermore, the crystal field level at approximately 13cm-1 is found to be both Raman and dipole active, indicating broken inversion symmetry in the system and thus undermining its current symmetry interpretation. In addition, evidence is found for a significant crystal field-phonon coupling in Tb2Ti2O7 . The additional crystal field information on Tb2Ti2O7 adds to the recent discussion on the low temperature symmetry of this system and may serve to improve its theoretical understanding.

  17. Thermodynamical Properties of Spin-3/2 Ising Model in a Longitudinal Random Field with Crystal Field

    Institute of Scientific and Technical Information of China (English)

    LIANGYa-Qiu; WEIGuo-Zhu; ZHANGHong; SONGGuo-Li

    2004-01-01

    A theoretical study of a spin-3/2 Ising model in a longitudinal random field with crystal field is studied by using of the effective-field theory with correlations. The phase diagrams and the behavior of the tricritical point are investigated numerically for the honeycomb lattice when the random field is bimodal. In particular, the specific heat and the internal energy are examined in detail for the system with a crystal-field constant in the critical region where the ground-state configuration may change from the spin-3/2 state to the spin-1/2 state. We find many interesting phenomena in the system.

  18. Thermodynamical Properties of Spin-3/2 Ising Model in a Longitudinal Random Field with Crystal Field

    Institute of Scientific and Technical Information of China (English)

    LIANG Ya-Qiu; WEI Guo-Zhu; ZHANG Hong; SONG Guo-Li

    2004-01-01

    A theoretical study of a spin-3/2 Ising model in a longitudinal random field with crystal field is studiedby using of the effective-field theory with correlations. The phase diagrams and the behavior of the tricritical point areinvestigated numerically for the honeycomb lattice when the randorm field is bimodal. In particular, the specific heatand the internal energy are examined in detail for the system with a crystal-field constant in the critical region wherethe ground-state configuration may change from the spin-3/2 state to the spin-1/2 state. We find many interestingphenomena in the system.

  19. Crystal-field study of magnetization and specific heat properties of frustrated pyrochlore Pr2Zr2O7

    Science.gov (United States)

    Alam, J.; Jana, Y. M.; Biswas, A. Ali

    2016-10-01

    The experimental results of temperature dependent dc magnetic susceptibility, field dependent isothermal magnetization, magnetic specific heat and entropy of the pyrochlore Pr2Zr2O7 are simulated and analyzed using appropriate D3d crystal-field (CF) and anisotropic molecular field tensors at Pr-sites in the self-consistent mean-field approach involving four magnetically non-equivalent rare-earth spins on the tetrahedral unit of the pyrochlore structure. CF level pattern and wave-functions of the ground 3H4 multiplet of the Pr3+ ions are obtained considering intermediate coupling between different Russell-Saunders terms of the 4f2 electronic configurations of Pr-ion and J-mixing effects. CF analysis shows that the CF ground-state of the Pr3+ ion in Pr2Zr2O7 is a well-isolated doublet, with significant admixtures of terms coming from |MJ=±4> and |MJ=±1>, and the Pr-spins are effectively Ising-like along the local axes. Magnetic specific heat in zero-field is simulated by considering a temperature dependence of the exchange splitting of the ground doublet.

  20. The Symmetry of Optical Field in Photonic Crystal Fibre with Trigonal Symmetry

    Directory of Open Access Journals (Sweden)

    Ivan Turek

    2006-01-01

    Full Text Available Some photographs of intensity of optical field of a photonic crystal fibre are presented in the contribution. Presented photographs document that the symmetry of photonic crystal creating the cladding of fibre is manifested in the symmetry of distribution of the optical field intensity. In case when more modes are excited in the fibre the symmetry of the generated field can be different as the symmetry of the eventual modes. How the symmetry may be changed is illustrated by amodel example.

  1. Anomalies in thermal expansion and heat capacity of TmB50 at low temperatures: magnetic phase transition and crystal electric field effect.

    Science.gov (United States)

    Novikov, V V; Zhemoedov, N A; Mitroshenkov, N V; Matovnikov, A V

    2016-11-01

    We experimentally study the heat capacity and thermal expansion of thulium boride (TmB50) at temperatures of 2-300 K. The wide temperature range (2-180 K) of boride negative expansion was revealed. We found the anomalies in C(T) heat capacity temperature dependence, attributed to the Schottky contribution (i.e. the influence of the crystal electric field: CEF), as well as the magnetic phase transition. CEF-splitting of the f-levels of the Tm(3+) ion was described by the Schottky function of heat capacity with a quasi-quartet in the ground state. Excited multiplets are separated from the ground state by energy gaps δ1 = 100 K, and δ2 ≈ 350 K. The heat capacity maximum at Tmax ≈ 2.4 K may be attributed to the possible magnetic transition in TmB50. Other possible causes of the low-temperature maximum of C(T) dependence are the nonspherical surroundings of rare earth atoms due to the boron atoms in the crystal lattice of the boride and the emergence of two-level systems, as well as the splitting of the ground multiplet due to local magnetic fields of the neighboring ions of thulium. Anomalies in heat capacity are mapped with the thermal expansion features of boride. It is found that the TmB50 thermal expansion characteristic features are due to the influence of the CEF, as well as the asymmetry of the spatial arrangement of boron atoms around the rare earth atoms in the crystal lattice of RB50. The Grüneisen parameters, corresponding to the excitation of different multiplets of CEF-splitting, were determined. A satisfactory accordance between the experimental and estimated temperature dependencies of the boride thermal expansion coefficient was achieved.

  2. Influence of magnetic field on the growth and properties of calcium tartrate crystals

    Energy Technology Data Exchange (ETDEWEB)

    Saban, K.V. E-mail: sabanvarkey@rediffmail.com; Jini, T.; Varghese, G

    2003-10-01

    The growth of calcium tartrate crystals in hydrosilica gel, in the presence of static magnetic fields has been investigated. Crystal formation at the free surface of the gel was studied under fields of strength up to 3 T. Weak magnetic fields created by permanent ferrite magnets were used to study the crystal formation in the gel column over long duration. The XRD spectra of the samples grown under magnetic fields exhibit increase in d values of most of the diffraction peaks and noticeable change in the intensity of reflections from certain planes. Application of the field resulted in the appearance of two additional absorption peaks in the IR spectrum of the material. Samples grown under fields of strength 1 and 3 T show paramagnetism up to 6 and 7 T, respectively, of the probing field strength. For stronger probing fields, the samples start exhibiting diamagnetism.

  3. Probing the sheath electric field with a crystal lattice by using thermophoresis in dusty plasma

    CERN Document Server

    Land, Victor; Matthews, Lorin; Hyde, Truell

    2010-01-01

    A two-dimensional dust crystal levitated in the sheath of a modified Gaseous Electronics Conference (GEC) reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained by measuring global characteristics of the levitated crystal obtained from top-view pictures. From the force balance, the electric field in the sheath is reconstructed. From the Bohm criterion, we conclude that the dust crystal is levitated mainly above and just below the classical Bohm point.

  4. Patterning technology for solution-processed organic crystal field-effect transistors

    OpenAIRE

    Yun Li; Huabin Sun; Yi Shi; Kazuhito Tsukagoshi

    2014-01-01

    Organic field-effect transistors (OFETs) are fundamental building blocks for various state-of-the-art electronic devices. Solution-processed organic crystals are appreciable materials for these applications because they facilitate large-scale, low-cost fabrication of devices with high performance. Patterning organic crystal transistors into well-defined geometric features is necessary to develop these crystals into practical semiconductors. This review provides an update on recent development...

  5. Spectroscopic and crystal field studies of Nd3+ in GdCa4O(BO3)3 and YCa4O(BO3)3

    Science.gov (United States)

    Lupei, A.; Antic-Fidancev, E.; Aka, G.; Vivien, D.; Aschehoug, P.; Goldner, Ph.; Pellé, F.; Gheorghe, L.

    2002-06-01

    The calcium rare-earth oxoborate crystals RCa4O(BO3)3-RCOB with R3+ as Gd3+ or Y3+ represent promising laser and nonlinear materials for the development of compact near IR and visible laser sources. New results on Nd3+ spectral characteristics in GdCOB and YCOB crystals in connection to the crystal structure are presented. Low-temperature absorption and selectively excited emission spectra of Nd3+ in RCOB crystals, grown by the Czochralski method in iridium crucible, present one prevailing center corresponding to Nd3+ ions in the R3+ site of Cs symmetry and at least three minority centers. Crystal field modeling gives a set of free ion and crystal field parameters that describe well the experimentally obtained energy level schemes for the main centers. A comparison between the Nd3+ crystal field splittings in RCOB and those of the C2 site in C-type Y 2O3 in terms of rare-earth environments is made. The selectively excited emission, lifetimes, and structural data were used to elucidate the nature of the minority centers. Two of the them were associated with Nd3+ in R3+ sites slightly perturbed by charged intrinsic lattice defects of nonstoichiometric or inversion Gd3+ (Y3+)Ca2+ type, while the third Nd3+ center is assigned to Nd3+ in a Ca2+ site. Other features of the spectra such as vibronics or homogeneous linewidths are also discussed. The Gaussian line shape and main contributions to inhomogeneous broadening are analyzed. An additional source of broadening for Nd3+ in YCOB is revealed.

  6. Hysteresis Loops and Phase Diagrams of the Spin-1 Ising Model in a Transverse Crystal Field

    Institute of Scientific and Technical Information of China (English)

    S. Bouhou; I. Essaoudi; A. Ainane; M. Saber; J. J. de Miguel; M. Kerouad1

    2012-01-01

    Within the framework of the effective-Geld theory with a probability distribution technique, which accounts for the self-spin correlation functions, the ferromagnetic spin-l Ising model with a transverse crystal field on honeycomb, square and simple cubic lattices is studied. We have investigated the effect of the transverse crystal field on the phase diagrams, magnetization, hysteresis loops and χz,h of the system. A number of interesting phenomena of the system are discussed.%Within the framework of the effective-field theory with a probability distribution technique,which accounts for the self-spin correlation functions,the ferromagnetic spin-1 Ising model with a transverse crystal field on honeycomb,square and simple cubic lattices is studied.We have investigated the effect of the transverse crystal field on the phase diagrams,magnetization,hysteresis loops and xz,h of the system.A number of interesting phenomena of the system are discussed.

  7. Characterizing configurable transmission modes in plasma photonic crystals using scanning field mapping

    Science.gov (United States)

    Wang, Benjamin; Cappelli, Mark

    2016-10-01

    A fully tunable plasma photonic crystal is used to control the propagation of free space electromagnetic waves in the S to X band of the microwave spectrum. A structured array of discharge plasma tubes are arranged in a square crystal lattice with the individual plasma dielectric constant tuned through variation in the plasma density. Microwave field-mapping is used to characterize the transmitted electromagnetic fields of the tunable device operating in waveguiding and bending modes. These modes are obtained by introducing appropriate line defects in the photonic crystal structure by controlling the activity of individual plasma tubes. Comparisons are made of the measured fields to those simulated using commercially-available software.

  8. Static magnetic susceptibility, crystal field and exchange interactions in rare earth titanate pyrochlores.

    Science.gov (United States)

    Malkin, B Z; Lummen, T T A; van Loosdrecht, P H M; Dhalenne, G; Zakirov, A R

    2010-07-14

    The experimental temperature dependence (T = 2-300 K) of single crystal bulk and site susceptibilities of rare earth titanate pyrochlores R(2)Ti(2)O(7) (R = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) is analyzed in the framework of crystal field theory and a mean field approximation. Analytical expressions for the site and bulk susceptibilities of the pyrochlore lattice are derived taking into account long range dipole-dipole interactions and anisotropic exchange interactions between the nearest neighbor rare earth ions. The sets of crystal field parameters and anisotropic exchange coupling constants have been determined and their variations along the lanthanide series are discussed.

  9. The effect of magnetic field on the shape of etch pits of paracetamol crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ivashchenko, V.E. [Kemerovo State University, Novosibirsk (Russian Federation); Research and Educational Center, Novosibirsk State University (Russian Federation); Boldyrev, V.V.; Shakhtshneider, T.P. [Institute of Solid State Chemistry and Mechanochemistry, RAS, Novosibirsk (Russian Federation); Zakharov, Yu.A.; Krasheninin, V.I. [Kemerovo State University, Novosibirsk (Russian Federation); Ermakov, A.E. [Institute of Physics of Metals, Ural Branch of RAS, Ekaterinburg (Russian Federation)

    2002-04-01

    In the present study we investigate the effect of magnetic field on the shape of etch pits of the crystals of p-hydroxyacetanilide (paracetamol), which is widely used in pharmacy as antipyretic, antiphlogistic medicine. It was discovered that the magnetic field (H=0.5 T, {tau}=15 min) changes the morphology of etch pits and shifts dislocations in paracetamol crystal. Activation energy of the changes induced by the action of the magnetic field was determined to be 63 kJ/mol, which is comparable with the energy of hydrogen bonds in crystal lattice. (orig.)

  10. Measuring 20-100 T B-fields using Zeeman splitting of sodium emission lines on a 500 kA pulsed power machine

    Science.gov (United States)

    Banasek, J. T.; Engelbrecht, J. T.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.

    2016-11-01

    We have shown that Zeeman splitting of the sodium (Na) D-lines at 5890 and 5896 Å can be used to measure the magnetic field (B-field) produced in high current pulsed power experiments. We have measured the B-field next to a return current conductor in a hybrid X-pinch experiment near a peak current of about 500 kA. Na is deposited on the conductor and then is desorbed and excited by radiation from the hybrid X-pinch. The D-line emission spectrum implies B-fields of about 20 T with a return current post of 4 mm diameter or up to 120 T with a return current wire of 0.455 mm diameter. These measurements were consistent or lower than the expected B-field, thereby showing that basic Zeeman splitting can be used to measure the B-field in a pulsed-power-driven high-energy-density (HED) plasma experiment. We hope to extend these measurement techniques using suitable ionized species to measurements within HED plasmas.

  11. Crystal field parameters and crystal field linewidths in the (REY)Pd/sub 3/ and (REY)Al/sub 2/ alloys

    Energy Technology Data Exchange (ETDEWEB)

    Walter, U.; Holland-Moritz, E.

    1981-12-01

    The LLW-parameters x and W of dilute rare earth impurities (RE = Pr, Nd, Tb, Dy, Ho, Er, Tm; c approx. equal to 0.05) in the cubic matrices YPd/sub 3/ and YAl/sub 2/ could be determined unequivocally in the crystal field scheme of Lea, Leask and Wolf by inelastic neutron scattering. The crystal field parameters derived from x and W are not consistent with the point charge model. The ratio of N(Esub(F))Jsub(ex) for the (REY)Al/sub 2/ extracted from the RE-linewidths correlates with the corresponding ratio extracted from their magnetic ordering temperatures.

  12. Zero-magnetic-field spin-splitting and the warping in the valence band of highly p-doped asymmetric AlGaAs/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Hirmer, Michael; Hirmer, M.; Schuh, D.; Wegscheider, W.; Korn, T.; Schueller, C. [Institut fuer Experimentelle Physik, Universitaet Regensburg, 93040 Regensburg (Germany)

    2011-07-01

    Zero-Magnetic-Field-Spin-Splitting (ZMFSS) in 2D quantum wells (QW) induced by the structure inversion asymmetry, and its control, are of major importance for both fundamental research and spintronic applications. In hole systems, the asymmetry leads to a ZMFSS of the heavy hole (HH) states in third order of the in-plane wave vector k. In our experiments, we focus on highly p-doped asymmetric AlGaAs/GaAs QW. We utilize electronic intersubband Raman measurements in backscattering geometry. In all samples we observe a low-energy spin-density excitation (SDE) with energies in the range of 0-3 meV. Samples with higher hole density show a two-component SDE. Comparing these excitation energies to 8 band k.p calculations of the valence subbands, the SDE can be interpreted as an intersubband excitation of the spin-split HH ground state, reflecting directly the ZMFSS. The two components can be attributed to different HH dispersions in different crystallographic directions, the so-called warping. We found that the observed spin splitting increases systematically with increasing hole density p, or by an external electric field. Measurements of the Shubnikov de Haas oscillations showed similar results.

  13. Influence of Superconductivity on Crystal Electric Field Transitions in La1-xTbxAl2

    DEFF Research Database (Denmark)

    Feile, R.; Loewenhaupt, M.; Kjems, Jørgen

    1981-01-01

    Inelastic neutron scattering from the crystal electric field transitions in La1-xTbxAl2 single crystals has revealed an abrupt increase in the lifetimes of these transitions when the system becomes superconducting. An increase in the integrated intensities is also observed. The lifetime effects...

  14. Coupling between crystal field transitions and phonons in the 4f-electron system CeCu 2

    Science.gov (United States)

    Schedler, R.; Witte, U.; Loewenhaupt, M.; Kulda, J.

    2003-07-01

    In general, elementary excitations like phonons and crystal field (CF) transitions are considered decoupled and the determination and interpretation of the measured spectra of both phenomena, i.e. the phonon dispersion relations and the CF level schemes are made independently of each other. A signature of a strong coupling between both phenomena is the observation of an unusual behaviour in both subsystems. In this paper, we present inelastic neutron scattering results on the rare earth compound CeCu 2. This substance shows a orthorhombic CeCu 2 structure with 18 phonon modes and a splitting of the J= {5}/{2} ground state multiplet of the Ce 3+ ions into 3 doublets. The assumption of a coupling between a CF transition connecting the two excited CF states and phonons was put forward from the results of inelastic neutron data on a polycrystalline sample. This assumption is now confirmed by inelastic neutron spectra on a single crystal showing unusual phonon energy shifts and line widths as well as a strong broadening of the CF excitations.

  15. Terahertz spectroscopy of crystal-field transitions in magnetoelectric TmA l3(BO3)4

    Science.gov (United States)

    Kuzmenko, A. M.; Mukhin, A. A.; Ivanov, V. Yu.; Komandin, G. A.; Shuvaev, A.; Pimenov, A.; Dziom, V.; Bezmaternykh, L. N.; Gudim, I. A.

    2016-11-01

    Dynamic magnetic properties of magnetoelectric TmA l3(BO3)4 borate have been investigated by terahertz spectroscopy. Crystal-field transitions within the ground multiplet 3H6 of T m3 + ions are observed and they are identified as magnetic-dipole transitions from the ground singlet A1 to the next excited doublet E of T m3 + ions. Unexpected fine structure of the transitions is detected at low temperatures. The new modes are assigned to local distortions of the sites with D3 symmetry by B i3 + impurities, which resulted in the splitting of the A1→E transition. Two types of locally distorted sites are identified and investigated. The main contribution to the static magnetic susceptibility is shown to be determined by the matrix elements of the observed magnetic transitions. We demonstrate that even in case of local distortions the symmetry of the undistorted crystal is recovered for magnetic and for quadratic magnetoelectric susceptibilities.

  16. Spin splitting at the high-magnetic-field phase transition of the organic conductor α-(BEDT-TTF)2KHg(SCN)4

    Science.gov (United States)

    Sasaki, Takahiko; Fukase, Tetsuo

    1999-06-01

    Spin splitting of the de Haas-van Alphen (dHvA) effect is studied in the quasi-two-dimensional organic conductor α-(BEDT-TTF)2KHg(SCN)4 by means of the magnetic torque method. The magnetic field direction dependence of the dHvA oscillation amplitude shows that the spin-splitting zero angles change at 23 T, where the phase transition magnetic field between the low-temperature, low-magnetic-field phase [antiferromagnetic (AF) phase] and the high-magnetic-field phase (M* phase) is. This change implies the increase of the g(mc/m0) value in the AF phase, where g is the g value, mc and m0 the cyclotron effective and free electron masses, respectively. The enhancement of the electron-electron interaction may be the origin of the large g(mc/m0) value in the AF phase. This result supports a model which requires a modification of the Lifshitz-Kosevich formulation in the AF phase in order to evaluate the effective mass and Dingle temperature correctly. In addition, anomalous structures on the magnetic torque curves are observed in both the AF and the M* phases. Each structure may correspond to the subsequent phase transitions by changing the magnetic field direction.

  17. Spectroscopy of Charge Carriers and Traps in Field-Doped Single Crystal Organic Semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xiaoyang [Columbia Univ., New York, NY (United States); Frisbie, Daniel [Univ. of Minnesota, Minneapolis, MN (United States)

    2017-03-31

    The proposed research aims to achieve quantitative, molecular level understanding of charge carriers and traps in field-doped crystalline organic semiconductors via in situ linear and nonlinear optical spectroscopy, in conjunction with transport measurements and molecular/crystal engineering.

  18. Mixed spin Ising model with four-spin interaction and random crystal field

    Energy Technology Data Exchange (ETDEWEB)

    Benayad, N., E-mail: n.benayad@fsac.ac.ma [Groupe de Mecanique Statistique, Laboratoire de physique theorique et appliquee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco); Laboratoire de physique des hautes energies et de la matiere condensee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco); Ghliyem, M. [Groupe de Mecanique Statistique, Laboratoire de physique theorique et appliquee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco); Laboratoire de physique des hautes energies et de la matiere condensee, Faculte des sciences-Aien Chock, Universite Hassan II-Casablanca, B.P 5366 Maarif, Casablanca 20100 (Morocco)

    2012-01-01

    The effects of fluctuations of the crystal field on the phase diagram of the mixed spin-1/2 and spin-1 Ising model with four-spin interactions are investigated within the finite cluster approximation based on a single-site cluster theory. The state equations are derived for the two-dimensional square lattice. It has been found that the system exhibits a variety of interesting features resulting from the fluctuation of the crystal field interactions. In particular, for low mean value D of the crystal field, the critical temperature is not very sensitive to fluctuations and all transitions are of second order for any value of the four-spin interactions. But for relatively high D, the transition temperature depends on the fluctuation of the crystal field, and the system undergoes tricritical behaviour for any strength of the four-spin interactions. We have also found that the model may exhibit reentrance for appropriate values of the system parameters.

  19. Imposed Orientation of Dye Molecules by Liquid Crystals and an Electric Field.

    Science.gov (United States)

    Sadlej-Sosnowska, Nina

    1980-01-01

    Describes experiments using dye solutions in liquid crystals in which polar molecules are oriented in an electrical field and devices are constructed to change their color in response to an electric signal. (CS)

  20. Research Progress on Photonic Crystals in the Field of Photocatalysis%光子晶体在光催化领域的研究进展

    Institute of Scientific and Technical Information of China (English)

    郭肃晋; 李德毅; 张永刚; 周雪飞; 张亚雷

    2013-01-01

    The application developments of photonic crystal in the field of photocatalysis are described, and the research progress of application of photocatalyst to water splitting into H2, photodegradation of organic pollutant are mainly introduced. Besides, further research work and improving direction of photonic crystal are proposed.%阐述了光子晶体在光催化领域中的应用进展,详细介绍了光子晶体作为光催化剂在废水处理及光解水制氢等领域的研究现状,并提出了光子晶体在该领域中未来改进的方向.

  1. Calculation of electrostatic fields in ionic crystals by a Bertaut method

    NARCIS (Netherlands)

    Weenk, J.W.; Harwig, H.A.

    1975-01-01

    A method to calculate the electrostatic field strength in ionic crystals is evaluated according to a model by Bertaut. Formulae for the self potential and the field strength at an ion site are derived. The practical use is demonstrated by calculations of field vectors in TiO2 (rutile, anatase, brook

  2. Low field investigations of single crystal Bi(2212): DC magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Shaw, G.; Murphy, S.D.; Bhagat, S.M. (Center for Superconductivity Research and Dept. of Physics and Astronomy, Univ. of Maryland, College Park (USA))

    1989-12-01

    DC Magnetization measurements on micaceous Bi(2212) single crystals suggest that; 1. for T< or approx.25 K the material is a bulk Superconductor (SC), 2. as T is increased, the interlayer coupling weakens, until for T> or approx.55 K the lamina become independent. (orig.).

  3. 高对称型声子晶体自准直弯曲及分束∗%Bending and splitting of self-collimated b eams in high symmetry sonic crystal

    Institute of Scientific and Technical Information of China (English)

    宋宗根; 邓科; 何兆剑; 赵鹤平

    2016-01-01

    Self-collimation, a peculiar effect that allows acoustic signals to propagate in sonic crystals (SCs) along a definite direction with almost no diffraction, possesses a promising prospect in integrated acoustics as it provides an effective way to transmit acoustic signals between on-chip functionalities. There exists, however, the intrinsic inability of self-collimation to efficiently bend and split acoustic signals. Most of existing schemes for bending and splitting of self-collimated acoustic beams are based on SC of square lattice, thus their bending and splitting angles are restricted to 90◦. In this paper, the finite element method is used to investigate self-collimation of acoustic beams in an SC of hexagonal lattice. It is shown that 60◦ and 120◦ bending of self-collimated acoustic waves can be simultaneously realized by simply truncating the two-dimensional hexagonal SC. Bended imaging for a point source with a subwavelength resolution of 0.38λ0 can also be realized by truncating the SC structure. In addition, a scheme for 60◦ and 120◦ splitting of self-collimated acoustic waves is also proposed by introducing line-defects into the hexagonal SC. It is demonstrated that an incoming self-collimated beam can be split into a 60◦ (or 120◦ bended one and a transmitted one, with the power ratio adjusted by the value of defect size. We believe that this hexagonal-SC-based bending and splitting mechanism will offer more flexibilities to the beam control in the design of acoustic devices and will be useful in integrated acoustic applications.

  4. Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

    Science.gov (United States)

    Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

    2002-01-01

    An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately

  5. Spin-orbit and tensor mean-field effects on spin-orbit splitting including self-consistent core polarizations

    CERN Document Server

    Zalewski, M; Satula, W; Werner, T R

    2008-01-01

    A new strategy of fitting the coupling constants of the nuclear energy density functional is proposed, which shifts attention from ground-state bulk to single-particle properties. The latter are analyzed in terms of the bare single-particle energies and mass, shape, and spin core-polarization effects. Fit of the isoscalar spin-orbit and both isoscalar and isovector tensor coupling constants directly to the f5/2-f7/2 spin-orbit splittings in 40Ca, 56Ni, and 48Ca is proposed as a practical realization of this new programme. It is shown that this fit requires drastic changes in the isoscalar spin-orbit strength and the tensor coupling constants as compared to the commonly accepted values but it considerably and systematically improves basic single-particle properties including spin-orbit splittings and magic-gap energies. Impact of these changes on nuclear binding energies is also discussed.

  6. THz near-field Faraday imaging in hybrid metamaterials

    NARCIS (Netherlands)

    Kumar, N.; Strikwerda, A.C.; Fan, K.; Zhang, X.; Averitt, R.D.; Planken, P.C.M.; Adam, A.J.L.

    2012-01-01

    We report on direct measurements of the magnetic near-field of metamaterial split ring resonators at terahertz frequencies using a magnetic field sensitive material. Specifically, planar split ring resonators are fabricated on a single magneto-optically active terbium gallium garnet crystal.

  7. THz near-field Faraday imaging in hybrid metamaterials

    NARCIS (Netherlands)

    Kumar, N.; Strikwerda, A.C.; Fan, K.; Zhang, X.; Averitt, R.D.; Planken, P.C.M.; Adam, A.J.L.

    2012-01-01

    We report on direct measurements of the magnetic near-field of metamaterial split ring resonators at terahertz frequencies using a magnetic field sensitive material. Specifically, planar split ring resonators are fabricated on a single magneto-optically active terbium gallium garnet crystal. Normall

  8. Phase field crystal study of deformation and plasticity in nanocrystalline materials.

    Science.gov (United States)

    Stefanovic, Peter; Haataja, Mikko; Provatas, Nikolas

    2009-10-01

    We introduce a modified phase field crystal (MPFC) technique that self-consistently incorporates rapid strain relaxation alongside the usual plastic deformation and multiple crystal orientations featured by the traditional phase field crystal (PFC) technique. Our MPFC formalism can be used to study a host of important phase transformation phenomena in material processing that require rapid strain relaxation. We apply the MPFC model to study elastic and plastic deformations in nanocrystalline materials, focusing on the "reverse" Hall-Petch effect. Finally, we introduce a multigrid algorithm for efficient numerical simulations of the MPFC model.

  9. Models of Mass Transport During Microgravity Crystal Growth of Alloyed Semiconductors in a Magnetic Field

    Science.gov (United States)

    Ma, Nancy

    2003-01-01

    Alloyed semiconductor crystals, such as germanium-silicon (GeSi) and various II-VI alloyed crystals, are extremely important for optoelectronic devices. Currently, high-quality crystals of GeSi and of II-VI alloys can be grown by epitaxial processes, but the time required to grow a certain amount of single crystal is roughly 1,000 times longer than the time required for Bridgman growth from a melt. Recent rapid advances in optoelectronics have led to a great demand for more and larger crystals with fewer dislocations and other microdefects and with more uniform and controllable compositions. Currently, alloyed crystals grown by bulk methods have unacceptable levels of segregation in the composition of the crystal. Alloyed crystals are being grown by the Bridgman process in space in order to develop successful bulk-growth methods, with the hope that the technology will be equally successful on earth. Unfortunately some crystals grown in space still have unacceptable segregation, for example, due to residual accelerations. The application of a weak magnetic field during crystal growth in space may eliminate the undesirable segregation. Understanding and improving the bulk growth of alloyed semiconductors in microgravity is critically important. The purpose of this grant to to develop models of the unsteady species transport during the bulk growth of alloyed semiconductor crystals in the presence of a magnetic field in microgravity. The research supports experiments being conducted in the High Magnetic Field Solidification Facility at Marshall Space Flight Center (MSFC) and future experiments on the International Space Station.

  10. Dependence of magnetization on crystal fields and exchange interactions in magnetite

    Energy Technology Data Exchange (ETDEWEB)

    Ouaissa, Mohamed, E-mail: m.ouaissa@yahoo.fr [Laboratoire de Génie Physique et Environnement, Faculté des Sciences, Université Ibn Tofail, Campus Universitaire BP 133, Kénitra 14000 (Morocco); Benyoussef, Abdelilah [Laboratory of Magnetism and Physics of High Energy, Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Abo, Gavin S. [Department of Electrical and Computer Engineering and MINT Center, The University of Alabama, Tuscaloosa, AL 35487 (United States); Ouaissa, Samia; Hafid, Mustapha [Laboratoire de Génie Physique et Environnement, Faculté des Sciences, Université Ibn Tofail, Campus Universitaire BP 133, Kénitra 14000 (Morocco); Belaiche, Mohammed [Laboratoire de Magnétisme, Matériaux Magnétiques, Microonde et Céramique, Ecole Normale Supérieure, Université Mohammed V-Agdal, B.P. 9235, Océan, Rabat (Morocco)

    2015-11-15

    In this work, we study the magnetization of magnetite (Fe{sub 3}O{sub 4}) with different exchange interactions and crystal fields using variational method based on the Bogoliubov inequality for the Gibbs free energy within the mean field theory. The magnetic behavior was investigated in the absence and presence of crystal fields. The investigations also revealed that the transition temperature depends on the crystal fields of the octahedral and tetrahedral sites. Magnetite exhibits ferrimagnetic phase with second order transition to paramagnetic phase at 850 K. This result is confirmed using the mean field theory within the Heisenberg model. Important factors that can affect the magnetic behavior of the system are exchange interactions and crystal field. Indeed, a new magnetic behavior was observed depending on these parameters. A first order phase transition from ferrimagnetic to ferromagnetic was found at low temperature, and a second order transition from ferromagnetic to paramagnetic was observed at high temperature. - Highlights: • Magnetization of magnetite versus temperature was studied by mean field theory. • The critical temperature of magnetite (Fe{sub 3}O{sub 4}) was approximately obtained. • Effect of sublattice crystal fields on the magnetization of Fe{sub 3}O{sub 4} was investigated.

  11. Influence of Acoustic Field Structure on Polarization Characteristics of Acousto-optic Interaction in Crystals

    Science.gov (United States)

    Muromets, A. V.; Trushin, A. S.

    Influence of acoustic field structure on polarization characteristics of acousto-optic interaction is investigated. It is shown that inhomogeneity of acoustic field and mechanism of ultrasound excitation causes changes in values of acousto-optic figure of merit for ordinary and extraordinary light beams in comparison with theoretic values. The theoretic values were derived under assumption that acoustic wave is homogeneous. Experimental analysis was carried out in acousto-optic cell based on lithium niobate crystal where the acoustic wave propagates at the angle 13 degrees to Z axis of the crystal. We used three different methods of ultrasound generation in the crystal: by means of external piezotransducer, by interdigital transducer and by two sets of electrodes placed on top of the crystal surface. In the latter case, the first pair of the electrodes was directed along X crystal axis, while the second pair of the electrodes was directed orthogonally to X crystal axis and the direction of ultrasound. Obtained values for diffraction efficiencies for ordinary and extraordinary polarized optical beams were qualitatively different which may be caused by spatial inhomogeneity of the generated acoustic waves in the crystal. Structure of acoustic field generated by these sets of electrodes was examined by laser probing. We performed the analysis of the acoustic field intensity using acousto-optic method. A relation of diffraction efficiencies for ordinary and extraordinary light waves was measured during each iteration of the laser probing.

  12. Coronal Magnetic Field Strength from Decameter Zebra-Pattern Observations: Complementarity with Band-Splitting Measurements of an Associated Type II Burst

    Science.gov (United States)

    Stanislavsky, A. A.; Konovalenko, A. A.; Koval, A. A.; Dorovskyy, V. V.; Zarka, P.; Rucker, H. O.

    2015-01-01

    A zebra pattern and a type II burst with band splitting were analyzed to study the coronal magnetic field in the height range of 1.9 - 2 solar radii. To this aim we used an extremely sensitive telescope (the Ukrainian decameter radio telescope, UTR-2) with a low-noise, high-dynamic-range spectrometer for the observations below 32 MHz. Based on the analysis of the spectral structures, the field strength obtained is 0.43 G. The value was found by fitting two different field indicators together under the assumptions that the shock wave front was perpendicular to the radial direction, and the radio emission of the type II burst was in the fundamental frequency. The result is compared to and agrees with coronal magnetic-field models.

  13. Ground-State Phase Diagram of Transverse Spin-2 Ising Model with Longitudinal Crystal-Field

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal-field is studied within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. The ground-state phase diagram and the tricritical point are obtained in the transverse field Ω/z J-longitudinal crystal D/zJ field plane. We find that there are the first order-order phase transitions in a very smallrange of D/zJ besides the usual first order-disorder phase transitions and the second order-disorder phase transitions.

  14. Gate-controlled zero-magnetic-field spin splitting in the valence band of asymmetric AlGaAs/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Hirmer, Michael; Hirmer, Marika; Schuh, Dieter; Wegscheider, Werner; Korn, Tobias; Schueller, Christian [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg (Germany)

    2010-07-01

    Zero-magnetic-field-spin-splitting (ZMFSS) in two-dimensional quantum wells (QW) induced by the structure inversion asymmetry, and its control, are of major importance for both fundamental research and spintronic applications, due to its influence on the dynamics and manipulation of the spin. In hole systems the asymmetry leads to a ZMFSS of the heavy hole (HH) states in third order of the in-plane wave vector k {sub parallel}. In our experiments, we focus on highly p-doped asymmetric 2D AlGaAs/GaAs quantum wells (QW). with different QW widths and spacer thicknesses and the manipulation of the Rashba spin splitting via top gates. We utilize electronic intersubband Raman measurements in backscattering geometry at 4.2 K. Using polarization selection rules, one can distinguish between charge-density excitation (CDE, polarized spectra) and spin-density excitation (SDE, depolarized spectra) in the Raman spectra. In all samples we observe a low-energy SDE with excitation energies in the range of 0-2 meV. Comparing these excitation energies to 8 band k.p calculations of the valence subbands, the SDE can be interpreted as an intersubband excitation of the spin-split HH ground state, reflecting directly the ZMFSS.

  15. Change in crystal structure and physical properties of the Multiferroics YMnO3 single crystals by Strong gravitational field

    Science.gov (United States)

    Tokuda, M.; Weijian, M.; Hayami, S.; Yoshiasa, A.; Mashimo, T.

    2017-04-01

    Many researchers have studied the multiferroicity of the hexagonal RMnO3 (R: rare-earth element) for both applications and fundamental studies. To investigate the relationship between the structure and physical properties of materials, some people apply the chemical pressure effect. The procedure of chemical pressure effect involves substituting rare-earth elements for ones which have a different ionic radius. Mashimo et al. have developed a high-temperature ultracentrifuge apparatus that can generate extended duration strong gravitational field in excess of 106 G under a wide range of temperatures (up to 500°C). Strong gravitational fields directly act on each atom as a different body force. This can cause the change in crystal structure. Thus, we subjected YMnO3 single crystal to strong gravity experiments (0.78×106 G, 400°C, 2 h) and investigated the resulting changes in the crystal structure and physical properties of the gravity sample. The single crystal four-circle X-ray diffraction measurements revealed the change in the nearest neighboring Mn-Mn and M-O bond distances. The temperature dependence of magnetic susceptibility by SQUID showed the change in the magnetic anisotropy of gravity sample.

  16. Splitting Ward identity

    Energy Technology Data Exchange (ETDEWEB)

    Safari, Mahmoud [Institute for Research in Fundamental Sciences (IPM), School of Particles and Accelerators, P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)

    2016-04-15

    Within the background-field framework we present a path integral derivation of the splitting Ward identity for the one-particle irreducible effective action in the presence of an infrared regulator, and make connection with earlier works on the subject. The approach is general in the sense that it does not rely on how the splitting is performed. This identity is then used to address the problem of background dependence of the effective action at an arbitrary energy scale. We next introduce the modified master equation and emphasize its role in constraining the effective action. Finally, application to general gauge theories within the geometric approach is discussed. (orig.)

  17. Split Malcev Algebras

    Indian Academy of Sciences (India)

    Antonio J Calderón Martín; Manuel Forero Piulestán; José M Sánchez Delgado

    2012-05-01

    We study the structure of split Malcev algebras of arbitrary dimension over an algebraically closed field of characteristic zero. We show that any such algebras is of the form $M=\\mathcal{U}+\\sum_jI_j$ with $\\mathcal{U}$ a subspace of the abelian Malcev subalgebra and any $I_j$ a well described ideal of satisfying $[I_j, I_k]=0$ if ≠ . Under certain conditions, the simplicity of is characterized and it is shown that is the direct sum of a semisimple split Lie algebra and a direct sum of simple non-Lie Malcev algebras.

  18. Composite Fermion Theory for the High Field Wigner Crystal State

    Science.gov (United States)

    Narevich, Romanas; Murthy, Ganpathy; Fertig, Herbert

    2001-03-01

    The low filling fraction Quantum Hall Effect is reexamined using the hamiltonian composite fermion theory developed by Shankar and Murthy(R. Shankar and G. Murthy, Phys. Rev. Lett. 79), 4437 (1997). We address the experiment by Jiang et. al.(H. W. Jiang et. al., Phys. Rev. B 44), 8107 (1991) where the insulating phase surrounding the ν=1/5 quantum liquid was observed and its activation energies (gaps) measured. Previous studies either found gaps that were off by few orders of magnitude (Hartree-Fock calculations of the electronic Wigner crystal(D. Yoshioka and H. Fukuyama, J. Phys. Soc. Japan 47), 394 (1979)) or were unable to calculate them because of the computational complexity (Monte-Carlo studies of the correlated crystal(H. Yi and H. A. Fertig, Phys. Rev. B 58), 4019 (1998)). We use the Hartree-Fock approximation for the periodic density state of composite fermions and find gaps that have a correct order of magnitude and reproduce the experimental dependence on the filling factor. We also report the results of the shear modulus calculation relevant for the collective pinning of the crystal.

  19. High-Field Magnetization in PrCo2Si2 Single Crystals

    Science.gov (United States)

    Shigeoka, Toru; Fujii, Hironobu; Yonenobu, Kenji; Sugiyama, Kiyohiro; Date, Muneyuki

    1989-02-01

    Magnetic properties of PrCo2Si2 single crystals have been studied by measurements of high-field magnetization, magnetic susceptibility and electrical resistivity. Anomalous behaviors in the resistivity appear at three successive magnetic phase transition temperatures of 9, 17 and 30K. The magnetic susceptibility is highly anisotropic and is analyzed using the single-ion Hamiltonian, including the crystal-field and molecular-field effects. The thermal variations of the susceptibilities can be well reproduced by the crystal-field parameters estimated from the point-charge model. Metamagnetic transitions with four steps are observable in the c-axis magnetization process up to 300 kOe. The magnetization process is discussed in terms of the incommensurate exchange field model in the Ising system proposed by Date.

  20. Phase diagrams of mixtures of a polymer and a cholesteric liquid crystal under an external field.

    Science.gov (United States)

    Matsuyama, Akihiko

    2014-11-14

    We present a mean field theory to describe phase behaviors in mixtures of a polymer and a cholesteric liquid crystal under an external magnetic or electric field. Taking into account a chiral coupling between a polymer and a liquid crystal under the external field, we examine twist-untwist phase transitions and phase separations in the mixtures. It is found that a cholesteric-nematic phase transition can be induced by not only the external field but also concentration and temperature. Depending on the strength of the external field, we predict cholesteric-paranematic (Ch+pN), nematic-paranematic (N+pN), cholesteric-nematic (Ch+N) phase separations, etc., on the temperature-concentration plane. We also discuss mixtures of a non-chiral nematic liquid crystal and a chiral dopant.

  1. Splitting Descartes

    DEFF Research Database (Denmark)

    Schilhab, Theresa

    2007-01-01

    Kognition og Pædagogik vol. 48:10-18. 2003 Short description : The cognitivistic paradigm and Descartes' view of embodied knowledge. Abstract: That the philosopher Descartes separated the mind from the body is hardly news: He did it so effectively that his name is forever tied to that division....... But what exactly is Descartes' point? How does the Kartesian split hold up to recent biologically based learning theories?...

  2. Crystal structure of a blue laccase from Lentinus tigrinus: evidences for intermediates in the molecular oxygen reductive splitting by multicopper oxidases

    Directory of Open Access Journals (Sweden)

    Golovleva Ludmila A

    2007-09-01

    Full Text Available Abstract Background Laccases belong to multicopper oxidases, a widespread class of enzymes implicated in many oxidative functions in pathogenesis, immunogenesis and morphogenesis of organisms and in the metabolic turnover of complex organic substances. They catalyze the coupling between the four one-electron oxidations of a broad range of substrates with the four-electron reduction of dioxygen to water. These catalytic processes are made possible by the contemporaneous presence of at least four copper ion sites, classified according to their spectroscopic properties: one type 1 (T1 site where the electrons from the reducing substrates are accepted, one type 2 (T2, and a coupled binuclear type 3 pair (T3 which are assembled in a T2/T3 trinuclear cluster where the electrons are transferred to perform the O2 reduction to H2O. Results The structure of a laccase from the white-rot fungus Lentinus (Panus tigrinus, a glycoenzyme involved in lignin biodegradation, was solved at 1.5 Å. It reveals a asymmetric unit containing two laccase molecules (A and B. The progressive reduction of the copper ions centers obtained by the long-term exposure of the crystals to the high-intensity X-ray synchrotron beam radiation under aerobic conditions and high pH allowed us to detect two sequential intermediates in the molecular oxygen reduction pathway: the "peroxide" and the "native" intermediates, previously hypothesized through spectroscopic, kinetic and molecular mechanics studies. Specifically the electron-density maps revealed the presence of an end-on bridging, μ-η1:η1 peroxide ion between the two T3 coppers in molecule B, result of a two-electrons reduction, whereas in molecule A an oxo ion bridging the three coppers of the T2/T3 cluster (μ3-oxo bridge together with an hydroxide ion externally bridging the two T3 copper ions, products of the four-electrons reduction of molecular oxygen, were best modelled. Conclusion This is the first structure of a

  3. Magnetic field controlled single crystal growth and surface modification of titanium alloys exposed for biocompatibility

    Science.gov (United States)

    Hermann, Regina; Uhlemann, Margitta; Wendrock, Horst; Gerbeth, Gunter; Büchner, Bernd

    2011-03-01

    The aim of this work is growth and characterisation of Ti55Nb45 (wt%) single crystals by floating-zone single crystal growth of intermetallic compounds using two-phase radio-frequency (RF) electromagnetic heating. Thereby, the process and, in particular, the flow field in the molten zone is influenced by additional magnetic fields. The growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. It is generally known that the crystallization process stability is enhanced if the crystallization interface is convex. For this, a tailored magnetic two-phase stirrer system has been developed, which enables a controlled influence on the melt ranging from intensive inwards to outwards flows. Since Ti is favourably light, strong and biocompatible, it is one of the few materials that naturally match the requirements for implantation in the human body. Therefore, the magnetic system was applied to crystal growth of Ti alloys. The grown crystals were oriented and cut to cubes with the desired crystallographic orientations [1 0 0] and [1 0 1] normally on a plane. The electron backscatter diffraction (EBSD) technique was applied to clearly determine crystal orientation and to localize grain boundaries. The formation of oxidic nanotubes on Ti surfaces in dependence of the grain orientation was investigated, performed electrochemically by anodic oxidation from fluoride containing electrolyte.

  4. Vertical electric field induced suppression of fine structure splitting of excited state excitons in a single GaAs/AlGaAs island quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ghali, Mohsen [Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan); Laboratory of Nanophotonics, Physics Department, Faculty of Science, Kafrelsheikh University, 33516 Kafrelsheikh (Egypt); Ohno, Yuzo; Ohno, Hideo [Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan)

    2015-09-21

    We report experimentally on fine structure splitting (FSS) of various excitonic transitions in single GaAs island quantum dots, formed by a monolayer thickness fluctuation in the narrow GaAs/AlGaAs quantum well, and embedded in an n-i-Schottky diode device. By applying a forward vertical electric field (F) between the top metallic contact and the sample substrate, we observed an in-plane polarization rotation of both the ground and the excited state excitons with increasing the electric field. The polarization rotations were accompanied with a strong decrease in the FSS of the ground as well as the excited state excitons with the field, until the FSS vanished as F approached 30 kV/cm.

  5. Light field distribution of general function photonic crystals

    CERN Document Server

    Wu, Xiang-Yao; Liu, Xiao-Jing; Zhang, Si-Qi; Wang, Jing; Ba, Nuo; Xiao, Li; Li, Hong

    2012-01-01

    In this paper, We have presented a new general function photonic crystals (GFPCs), which refractive indexes are line functions of space position in two mediums $A$ and $B$, and obtain new results: (1) when the line function of refractive indexes is up or down, the transmissivity can be far larger or smaller than 1. (2) when the refractive indexes function increase or decrease along the direction of incident light, the light intensity should be magnified or weaken, which can be made optical magnifier or attenuator. (3) The GFPCs can be made optical diode when the light positive and negative incident the GFPCs.

  6. Scientists summit at Shanghai in the field of polymer crystallization

    Institute of Scientific and Technical Information of China (English)

    Wenbing HU

    2009-01-01

    @@ From Aug. 12 to 15 at Galaxy Hotel, Shanghai, more than 100 scientists and graduate students from macromolecular phy-sics, engineering and chemistry met together in the Interna-tional Discussion Meeting of Polymer Crystallization (IDMPC). The participants were coming from China, Japan, United States, Germany, England, France, Netherlands, Italy, Korea and Canada. The meeting was initiated by the Ministry of Education of China and European Physical Society, sponsored by the National Natural Science Foundation of China and Donghua University, and organized by the State Key Laboratory for Modification of Chemical Fibers and Chemical Materials.

  7. Trapped field of 1.1 T without flux jumps in an MgB2 bulk during pulsed field magnetization using a split coil with a soft iron yoke

    Science.gov (United States)

    Fujishiro, H.; Mochizuki, H.; Ainslie, M. D.; Naito, T.

    2016-08-01

    MgB2 superconducting bulks have promising potential as trapped field magnets. We have achieved a trapped field of B z = 1.1 T on a high-J c MgB2 bulk at 13 K without flux jumps by pulsed field magnetization (PFM) using a split-type coil with a soft iron yoke, which is a record-high trapped field by PFM for bulk MgB2 to date. The flux jumps, which frequently took place using a solenoid-type coil during PFM, were avoided by using the split-type coil, and the B z value was enhanced by the insertion of soft iron yoke. The flux dynamics and heat generation/propagation were analyzed during PFM using a numerical simulation, in which the magnetic flux intruded and attenuated slowly in the bulk and tended to align along the axial direction due to the presence of soft iron yoke. The advantages of the split-type coil and the simultaneous use of a soft iron yoke are discussed.

  8. Electric-field variations within a nematic-liquid-crystal layer.

    Science.gov (United States)

    Cummings, L J; Mema, E; Cai, C; Kondic, L

    2014-07-01

    A thin layer of nematic liquid crystal (NLC) across which an electric field is applied is a setup of great industrial importance in liquid crystal display devices. There is thus a large literature modeling this situation and related scenarios. A commonly used assumption is that an electric field generated by electrodes at the two bounding surfaces of the layer will produce a field that is uniform: that is, the presence of NLC does not affect the electric field. In this paper, we use calculus of variations to derive the equations coupling the electric potential to the orientation of the NLC's director field, and use a simple one-dimensional model to investigate the limitations of the uniform field assumption in the case of a steady applied field. The extension of the model to the unsteady case is also briefly discussed.

  9. Reorientation of single-wall carbon nanotubes in negative anisotropy liquid crystals by an electric field

    Directory of Open Access Journals (Sweden)

    Amanda García-García

    2016-06-01

    Full Text Available Single-wall carbon nanotubes (SWCNT are anisotropic nanoparticles that can cause modifications in the electrical and electro-optical properties of liquid crystals. The control of the SWCNT concentration, distribution and reorientation in such self-organized fluids allows for the possibility of tuning the liquid crystal properties. The alignment and reorientation of CNTs are studied in a system where the liquid crystal orientation effect has been isolated. Complementary studies including Raman spectroscopy, microscopic inspection and impedance studies were carried out. The results reveal an ordered reorientation of the CNTs induced by an electric field, which does not alter the orientation of the liquid crystal molecules. Moreover, impedance spectroscopy suggests a nonnegligible anchoring force between the CNTs and the liquid crystal molecules.

  10. Excess vibrational modes of a crystal in an external non-affine field

    Indian Academy of Sciences (India)

    SASWATI GANGULY; SURAJIT SENGUPTA

    2017-07-01

    Thermal displacement fluctuations in a crystal may be classified as either “affine” or “non-affine”. While the former couples to external stress with familiar consequences, the response of a crystal when nonaffine displacements are enhanced using the thermodynamically conjugate field, is relatively less studied. We examine this using a simple model of a crystal in two dimensions for which analytical calculations are possible. Enhancing non-affine fluctuations destabilises the crystal. The population of small frequency phonon modesincreases, with the phonon density of states shifting, as a whole, towards zero frequency. Even though the crystal is free of disorder, we observe growing length and time scales. Our results, which may have implications for the glass transition and structural phase transitions in solids, are compared to molecular dynamics simulations. Possibility of experimental verification of these results is also discussed.

  11. Reorientation of single-wall carbon nanotubes in negative anisotropy liquid crystals by an electric field

    Science.gov (United States)

    García-García, Amanda; Vergaz, Ricardo; Algorri, José F; Zito, Gianluigi; Cacace, Teresa; Marino, Antigone; Otón, José M

    2016-01-01

    Summary Single-wall carbon nanotubes (SWCNT) are anisotropic nanoparticles that can cause modifications in the electrical and electro-optical properties of liquid crystals. The control of the SWCNT concentration, distribution and reorientation in such self-organized fluids allows for the possibility of tuning the liquid crystal properties. The alignment and reorientation of CNTs are studied in a system where the liquid crystal orientation effect has been isolated. Complementary studies including Raman spectroscopy, microscopic inspection and impedance studies were carried out. The results reveal an ordered reorientation of the CNTs induced by an electric field, which does not alter the orientation of the liquid crystal molecules. Moreover, impedance spectroscopy suggests a nonnegligible anchoring force between the CNTs and the liquid crystal molecules. PMID:27547599

  12. Tunable defect modes in 2D photonic crystals by means of external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Soltani Vala, A., E-mail: asoltani@tabrizu.ac.i [Physics Department, University of Tabriz, Tabriz (Iran, Islamic Republic of); Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of); Rezaei, B. [Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of); Kalafi, M. [Physics Department, University of Tabriz, Tabriz (Iran, Islamic Republic of); Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of)

    2010-07-15

    We investigate the tunable defect modes in 2D photonic crystal of silicon rods in air background in which one of the rods is replaced by ferrite material and an external static magnetic field is applied in the ferrite rod direction. Using the supercell method, the dependence of E-polarized defect modes on the magnetic field has been reported.

  13. Transport through a Finite One-Dimensional Crystal

    NARCIS (Netherlands)

    Kouwenhoven, L.P.; Hekking, F.W.J.; Wees, B.J. van; Harmans, C.J.P.M.; Timmering, C.E.; Foxon, C.T.

    1990-01-01

    We have studied the magnetotransport properties of an artificial one-dimensional crystal. The crystal consists of a sequence of fifteen quantum dots, defined in the two-dimensional electron gas of a GaAs/AlGaAs heterostructure by means of a split-gate technique. At a fixed magnetic field of 2 T, two

  14. Two Beam Energy Exchange in Hybrid Liquid Crystal Cells with Photorefractive Field Controlled Boundary Conditions (Postprint)

    Science.gov (United States)

    2016-09-12

    AFRL-RX-WP-JA-2017-0209 TWO BEAM ENERGY EXCHANGE IN HYBRID LIQUID CRYSTAL CELLS WITH PHOTOREFRACTIVE FIELD CONTROLLED BOUNDARY...DATES COVERED (From - To) 29 August 2016 Interim 26 October 2015 – 29 July 2016 4. TITLE AND SUBTITLE TWO BEAM ENERGY EXCHANGE IN HYBRID LIQUID... energy gain when two light beams intersect in a hybrid nematic liquid crystal (LC) cell with photorefractive crystalline substrates. A periodic space

  15. Liquid crystal cell design of VGA field sequential color LCoS display

    Science.gov (United States)

    Liu, Yanyan; Geng, Weidong; Dai, Yongping

    2009-07-01

    The design of liquid crystal cell is an important factor to determine the display quality of LCoS display device. The goal of this paper is to gain VGA field sequential color (FSC) LCoS device used for near-to-eye system. The characteristics of optics and electrooptics for the twist nematic liquid crystal material and the material requirements of the FSC LCoS were studied. The LCOS liquid crystal cell optimized by dynamic parameter space method had an uniform reflectivity (about 90%) for the light with wave length from 450nm to 650nm. Both considering the electrooptic response curve of liquid crystal and the relationship between the contrast ratio and pixel size, we determined to use high speed twist nematic liquid crystal working in normally white mode. The liquid crystal cell gap and the pixel size were determined as 2.5um and 12um, respectively. The VGA FSC LCoS device was fabricated with SMIC 0.35um CMOS process and filled with LC-A liquid crystal of Merck in Varitronix. The measurement showed that the response time of liquid crystal from light to dark was 1.8ms and from dark to light was 4.4ms. The contrast ratio is bigger than 50:1. The LCoS displays well.

  16. Detection of Flux Emergence, Splitting, Merging, and Cancellation of Network Fields. II Apparent Unipolar Flux Change and Cancellation

    CERN Document Server

    Iida, Y; Yokoyama, T

    2015-01-01

    In this second paper in the series, we investigate occurrence frequencies of apparent unipolar processes, cancellation, and emergence of patch structures in quiet regions. Apparent unipolar events are considerably more frequent than cancellation and emergence as per our definition, which is consistent with Lamb et al. (2013). Furthermore, we investigate the frequency distributions of changes in flux during apparent unipolar processes are and found that they concentrate around the detection limit of the analysis. Combining these findings with the results of our previous paper, Iida et al. (2012), that merging and splitting are more dominant than emergence and cancellation, these results support the understanding that apparent unipolar processes are actually interactions with and among patches below the detection limit and that there still are numerous flux interactions between the flux range in this analysis and below the detection limit. We also investigate occurrence frequency distributions of flux decrease ...

  17. Atomic density functional and diagram of structures in the phase field crystal model

    Science.gov (United States)

    Ankudinov, V. E.; Galenko, P. K.; Kropotin, N. V.; Krivilyov, M. D.

    2016-02-01

    The phase field crystal model provides a continual description of the atomic density over the diffusion time of reactions. We consider a homogeneous structure (liquid) and a perfect periodic crystal, which are constructed from the one-mode approximation of the phase field crystal model. A diagram of 2D structures is constructed from the analytic solutions of the model using atomic density functionals. The diagram predicts equilibrium atomic configurations for transitions from the metastable state and includes the domains of existence of homogeneous, triangular, and striped structures corresponding to a liquid, a body-centered cubic crystal, and a longitudinal cross section of cylindrical tubes. The method developed here is employed for constructing the diagram for the homogeneous liquid phase and the body-centered iron lattice. The expression for the free energy is derived analytically from density functional theory. The specific features of approximating the phase field crystal model are compared with the approximations and conclusions of the weak crystallization and 2D melting theories.

  18. Semiconductor crystal growth in crossed electric and magnetic fields: Center Director's Discretionary Fund

    Science.gov (United States)

    Mazuruk, K.; Volz, M. P.

    1996-01-01

    A unique growth cell was designed in which crossed electric and magnetic fields could be separately or simultaneously applied during semiconductor crystal growth. A thermocouple was inserted into an InSb melt inside the growth cell to examine the temperature response of the fluid to applied electromagnetic fields. A static magnetic field suppressed time-dependent convection when a destabilizing thermal field was applied. The simultaneous application of electric and magnetic fields resulted in forced convection in the melt. The InSb ingots grown in the cell were polycrystalline. An InGaSb crystal, 0.5 cm in diameter and 23-cm long, was grown without electromagnetic fields applied. The axial composition results indicated that complete mixing in the melt occurred for this large aspect ratio.

  19. Random crystal field effect on the magnetic and hysteresis behaviors of a spin-1 cylindrical nanowire

    Science.gov (United States)

    Zaim, N.; Zaim, A.; Kerouad, M.

    2017-02-01

    In this work, the magnetic behavior of the cylindrical nanowire, consisting of a ferromagnetic core of spin-1 atoms surrounded by a ferromagnetic shell of spin-1 atoms is studied in the presence of a random crystal field interaction. Based on Metropolis algorithm, the Monte Carlo simulation has been used to investigate the effects of the concentration of the random crystal field p, the crystal field D and the shell exchange interaction Js on the phase diagrams and the hysteresis behavior of the system. Some characteristic behaviors have been found, such as the first and second-order phase transitions joined by tricritical point for appropriate values of the system parameters, triple and isolated critical points can be also found. Depending on the Hamiltonian parameters, single, double and para hysteresis regions are explicitly determined.

  20. Crystal fields of Pr sup 3 sup + in LiYF sub 4 under pressure

    CERN Document Server

    Tröster, T

    2003-01-01

    Fluorescence spectra of LiYF sub 4 :Pr sup 3 sup + have been measured between 12,000 and 22,000 cm sup - sup 1 under pressures up to 10 GPa. In total, 25 crystal field energy levels were obtained and used for the determination of free-ion and crystal field parameters under pressure. According to the nephelauxetic effect, the free-ion parameters decrease with increasing pressure. The relative decrease is larger for the Slater than for the spin-orbit coupling parameter. This behavior is consistent with former studies on Pr sup 3 sup + in different crystals and can be explained by a special covalency model. According to an effective D sub 2 sub d symmetry, five crystal field parameters B sub 0 sup 2 (f,f), B sub 0 sup 4 (f,f), B sub 4 sup 4 (f,f), B sub 0 sup 6 (f,f), and B sub 4 sup 6 (f,f) are non-zero. The pressure-induced changes of these parameters have been determined up to the maximum pressure of 10 GPa. In order to improve the calculation of the crystal field levels, the configuration interactions with t...

  1. Zero-field nuclear magnetic resonance of a nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Thayer, A.M.; Millar, J.M.; Luzar, M.; Jarvie, T.P.; Pines, A.

    1986-04-10

    The molecular order parameter of CH/sub 2/Cl/sub 2/ in a nematic liquid crystal was measured by using a version of zero-field NMR employing pulsed dc magnetic fields. Spectral frequencies and intensities are shown to reflect the ordering on a molecular and macroscopic scale, respectively. Samples oriented in high magnetic field did not significantly change their state of alignment during the time scale of the field cycle. Zero-field measurements of the order parameter yielded values within experimental error of those measured in high field. A zero-field echo experiment was performed to decrease the effect of residual fields on line width. Dipolar order was created in zero field by using a pulsed dc field analogue of the Jeener-Brokaert experiment. 26 references, 8 figures.

  2. Link between optical spectra, crystal-field parameters, and local environments of Eu3+ ions in Eu2O3-doped sodium disilicate glass

    Science.gov (United States)

    Qin, T.; Mountjoy, G.; Afify, N. D.; Reid, M. F.; Yeung, Y. Y.; Speghini, A.; Bettinelli, M.

    2011-09-01

    Rare-earth-doped glasses are key materials for optical technology due to the luminescent properties of 4fn ions. The crystal-field model describes the effect of local environment on transitions between 4f electrons. We present a detailed modeling study of the optical spectra of sodium disilicate glass, 33Na2O·67SiO2, doped with 0.2% and 1.0 mol% Eu2O3. This study uses very large molecular dynamics models with up to 100 Eu3+ ions, the superposition model for covalent and overlap effects on crystal-field parameters, and realistic values for homogeneous linewidth broadening. The simulated spectra are in reasonable agreement with experiment. The trends in 7FJ energy levels across different Eu3+ ion sites have been examined and a very detailed analysis is presented that looks at how features of the spectra are related to features of the local environment of Eu3+ ions. Increasing the crystal-field strength Stotal causes the 7F0 energy level to decrease and causes the splitting of 7FJ manifolds to increase, and this is due to increasing mixing of 4f wave functions. To a reasonable approximation the crystal-field strength components Sk depend on angular positions of ligands independently of distances to ligands. The former are seen to be more significant in determining Sk, which are closely related to the rotationally invariant bond-orientational order parameters Qk. The values of S2 are approximately linear in Q2, and the values of Q2 are higher for fivefold than sixfold coordinated rare-earth ions. These results can be of importance for efforts to enhance the local environment of rare-earth ions in oxide glasses for optical applications.

  3. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics

    Science.gov (United States)

    Pyzer-Knapp, Edward O.; Thompson, Hugh P. G.; Day, Graeme M.

    2016-01-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  4. Crystal field of Dy in non-magnetic metals

    NARCIS (Netherlands)

    Kikkert, Pieter Jan Willem

    1980-01-01

    Many investigations carried out during the last 15 years have demonstrated that the crystalline electric field (CEF) has a great influence on the low temperature magnetic behaviour of rare earth ions in metallic systems (see e.g. /1/) . It is therefore important to understand the origin of the CEF i

  5. Crystal field excitations in the cubic compound Ce{sub 3}Rh{sub 4}Sn{sub 13}

    Energy Technology Data Exchange (ETDEWEB)

    Adroja, D.T. [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX (United Kingdom)], E-mail: d.t.adroja@rl.ac.uk; Strydom, A.M. [Department of Physics APK, University of Johannesburg (South Africa); Murani, A.P. [Institut Laue Langevin, F-38042 Grenoble Cedex (France); Kockelmann, W.A. [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX (United Kingdom); Fraile, A. [Laboratorio de Magnetismo, Dpto de Fisica de Materia Condensada and Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza, 50009 Zaragoza (Spain)

    2008-04-01

    The recent heat capacity measurements of Ce{sub 3}Rh{sub 4}Sn{sub 13} have revealed a broad peak at 1 K with an entropy of 3R ln(2) per f.u., but no clear sign of any magnetic ordering down to 100 mK. In order to understand this anomalous heat capacity behaviour of Ce{sub 3}Rh{sub 4}Sn{sub 13}, we have carried out low- and high-energy inelastic neutron scattering measurements. Our high-energy studies reveal two well-resolved crystal field (CF) excitations at {approx}9 meV and 38 meV. The observation of two CF excitations in the cubic structure of Ce{sub 3}Rh{sub 4}Sn{sub 13} could be explained on the basis of tetragonal point symmetry of the Ce ions. Interestingly, the low-energy measurements apparently show, or are best described by, a quasi-elastic peak and an inelastic peak at {approx}0.2 meV at 1.5 K, both of Lorentzian shape. We attribute the low-energy peak to Zeeman splitting of the ground state doublet, in the presence of short range magnetic ordering. Further, the low-energy peak explains the observed anomaly in the heat capacity.

  6. Relation between stabilization energy, crystal field coefficient and themagnetic exchange interaction for Tb3+ ion

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xiangmu; MA Wenjuan; CUI Shuwen; WANG Lihua

    2006-01-01

    Based on a single ion model, Hamiltonian of the simplest form about magnetocrystalline anisotropy for Tb3+ ion was solved by using the numerical method. The relation between the stabilization energy, crystal field coefficient B20 and the magnetic exchange interaction was studied as temperature approaches to 0K. The results show that the stabilization energy contributed by Tb3+ is linear with crystal field coefficient B20 approximately, but it is insensitive to the change of magnetic exchange interaction for the strong magnetic substancessuch as TbCo5, Tb2Co17 and Tb2Fe14B compounds.

  7. Organic single crystals or crystalline micro/nanostructures: Preparation and field-effect transistor applications

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Organic single crystals hold great promise for the development of organic semiconductor materials,because they could reveal the intrinsic electronic properties of these materials,providing high-performance electronic devices and probing the structureproperty relationships.This article reviews the preparation methods for organic single crystals or crystalline micro/nanostructures,including vapor phase growth methods and solution-processed methods,and summarizes a few methods employed in the fabrication of field-effect transistors along with dozens of examples concerning both small molecules and polymers with high field-effect performance.

  8. Electric field-induced optical second harmonic generation in nematic liquid crystal 5CB

    Science.gov (United States)

    Torgova, S. I.; Shigorin, V. D.; Maslyanitsyn, I. A.; Todorova, L.; Marinov, Y. G.; Hadjichristov, G. B.; Petrov, A. G.

    2014-12-01

    Electric field-induced second harmonic generation (EFISH) was studied for the liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) (a nematic phase material at room temperature). The intensity of coherent SHG from 5CB cells upon DC electric field was measured for various initial orientations of the liquid crystal. The dependence of the SHG intensity on the pump beam incidence angle was obtained in transmission geometry using sample rotation method. The experimental results (the registered light intensity in the output SHG interference patterns) were theoretically modelled and analyzed.

  9. A single-gap transflective liquid crystal driven by fringe and vertical electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Young Jin; Chin, Mi Hyung; Kim, Jin Ho; Her, Jung Hwa; Lee, Seung Hee [Polymer BIN Fusion Research Center, Department of Polymer Nano-Science and Technology, Chonbuk National University, Chonju, Chonbuk 561-756 (Korea, Republic of); Jin, Hyun Suk; Kim, Byeong Koo, E-mail: lsh1@chonbuk.ac.k [Mobile Product Development Department, LG Display Co., Ltd., Gumi, Gyungbuk 730-350 (Korea, Republic of)

    2009-07-21

    A single-gap transflective liquid-crystal display driven by a fringe electric field in the transmissive (T) region and a vertical electric field in the reflective (R) region was designed. In the device, a homogeneously aligned liquid crystal (LC) rotates almost in plane by a fringe field in the T-region whereas the LC tilts upwards by a vertical field in the R-region. A high surface pre-tilt angle of the LC in the R-region is achieved through polymerization of an UV curable reactive mesogen monomer at the surfaces and thus the effective cell retardation in the R-region becomes half of that in the T-region. Consequently, a transflective display driven by a vertical and a fringe electric field with a single cell gap and single gamma curves is realized.

  10. Striations in CZ silicon crystals grown under various axial magnetic field strengths

    Science.gov (United States)

    Kim, K. M.; Smetana, P.

    1985-10-01

    Inhibition of fluid flow instabilities in the melt by the axial magnetic field in Czochralski silicon crystal growth (AMCZ) is investigated precisely by a high-sensitivity striation etch in conjunction with temperature measurements. The magnetic field strength (B) was varied up to 4.0 kG, incremented mostly in 0.5-kG/2.5-cm crystal length. The convection flow was substantially suppressed at B greater than or equal to 1.0 kG. A low oxygen level of 2-3 ppm and a high resistivity of 400 ohm-cm is achieved in the AMCZ silicon crystals at B greater than or equal to 1.0 kG. Random striations at B = O, characteristic of turbulent convection, assumed progressively a periodicity, indicative of oscillatory convection at B from 0.35-4.0 kG. The striation contrast or 'intensity' decreased steadily with the increase in B. At B = 4 kG, most of the crystal was free of striations, although some weak, localized periodic striations persisted near the crystal periphery. Spreading-resistance measurement shows, however, a uniform dopant distribution in all crystal sections grown at B from 0.35-4.0 kG within a few percent.

  11. Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

    Science.gov (United States)

    Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

    2002-11-01

    An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately

  12. Terahertz radiation-induced sub-cycle field electron emission across a split-gap dipole antenna

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jingdi; Averitt, Richard D., E-mail: xinz@bu.edu, E-mail: raveritt@ucsd.edu [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Department of Physics, Boston University, Boston, Massachusetts 02215 (United States); Zhao, Xiaoguang; Fan, Kebin; Wang, Xiaoning; Zhang, Xin, E-mail: xinz@bu.edu, E-mail: raveritt@ucsd.edu [Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215 (United States); Zhang, Gu-Feng [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Geng, Kun [Department of Physics, Boston University, Boston, Massachusetts 02215 (United States)

    2015-12-07

    We use intense terahertz pulses to excite the resonant mode (0.6 THz) of a micro-fabricated dipole antenna with a vacuum gap. The dipole antenna structure enhances the peak amplitude of the in-gap THz electric field by a factor of ∼170. Above an in-gap E-field threshold amplitude of ∼10 MV/cm{sup −1}, THz-induced field electron emission is observed as indicated by the field-induced electric current across the dipole antenna gap. Field emission occurs within a fraction of the driving THz period. Our analysis of the current (I) and incident electric field (E) is in agreement with a Millikan-Lauritsen analysis where log (I) exhibits a linear dependence on 1/E. Numerical estimates indicate that the electrons are accelerated to a value of approximately one tenth of the speed of light.

  13. Terahertz radiation-induced sub-cycle field electron emission across a split-gap dipole antenna

    CERN Document Server

    Zhang, Jingdi; Fan, Kebin; Wang, Xiaoning; Zhang, Gu-Feng; Geng, Kun; Zhang, Xin; Averitt, Richard D

    2015-01-01

    We use intense terahertz pulses to excite the resonant mode (0.6 THz) of a micro-fabricated dipole antenna with a vacuum gap. The dipole antenna structure enhances the peak amplitude of the in-gap THz electric field by a factor of ~170. Above an in-gap E-field threshold amplitude of ~10 MVcm-1, THz-induced field electron emission is observed (TIFEE) as indicated by the field-induced electric current across the dipole antenna gap. Field emission occurs within a fraction of the driving THz period. Our analysis of the current (I) and incident electric field (E) is in agreement with a Millikan-Lauritsen analysis where log (I) exhibits a linear dependence on 1/E. Numerical estimates indicate that the electrons are accelerated to a value of approximately one tenth of the speed of light.

  14. Dark-field transmission electron microscopy of cortical bone reveals details of extrafibrillar crystals.

    Science.gov (United States)

    Schwarcz, Henry P; McNally, Elizabeth A; Botton, Gianluigi A

    2014-12-01

    In a previous study we showed that most of the mineral in bone is present in the form of "mineral structures", 5-6nm-thick, elongated plates which surround and are oriented parallel to collagen fibrils. Using dark-field transmission electron microscopy, we viewed mineral structures in ion-milled sections of cortical human bone cut parallel to the collagen fibrils. Within the mineral structures we observe single crystals of apatite averaging 5.8±2.7nm in width and 28±19nm in length, their long axes oriented parallel to the fibril axis. Some appear to be composite, co-aligned crystals as thin as 2nm. From their similarity to TEM images of crystals liberated from deproteinated bone we infer that we are viewing sections through platy crystals of apatite that are assembled together to form the mineral structures.

  15. Analyses of crystal field and exchange interaction of Dy3Ga5O12 under extreme conditions

    Institute of Scientific and Technical Information of China (English)

    Wang Wei; Qi Xin; Yue Yuan

    2011-01-01

    This paper theoretically investigates the effects of crystal field and exchange interaction field on magnetic properties in dysprosium gallium garnet under extreme conditions (low temperatures and high magnetic fields) based on quantum theory. Here, five sets of crystal field parameters are discussed and compared. It demonstrates that, only considering the crystal field effect, the experiments can not be successfully explained. Thus, referring to the molecular field theory,an effective exchange field associated with the Dy-Dy exchange interaction is further taken into account. Under special consideration of crystal field and the exchange interaction field, it obtains an excellent agreement between the theoretical results and experiments, and further confirms that the exchange interaction field between rare-earth ions has great importance to magnetic properties in paramagnetic rare-earth gallium garnets.

  16. Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals

    Science.gov (United States)

    Śliwa, I.; JeŻewski, W.; Kuczyński, W.

    2016-01-01

    Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples.

  17. Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals.

    Science.gov (United States)

    Śliwa, I; Jeżewski, W; Kuczyński, W

    2016-01-01

    Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples.

  18. Optical spectroscopy and crystal field studies of the Mn{sup 4+} ion (3d{sup 3}) in the double perovskite NaLaMgTeO{sub 6}

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Alok M.; Camardello, Samuel J.; Comanzo, Holly A.; Garcia-Santamaria, Florencio [GE Global Research, Niskayuna, NY (United States); Brik, Mikhail G. [Tartu Univ. (Estonia). Inst. of Physics

    2014-02-15

    The spectroscopic properties of the Mn{sup 4+} ion (3d{sup 3}) in the double perovskite NaLaMgTeO{sub 6} are reported in this work. Evidence is presented for the occupation by the Mn{sup 4+} ion of both the six coordinated Mg{sup 2+} and Te{sup 6+} sites in the host structure. The Mn{sup 4+} energy levels are calculated using the exchange charge model of crystal field theory for both occupied sites. The results of our calculations yield the crystal field splitting and Racah parameters of Dq =2008 cm{sup -1}, B =790 cm{sup -1}, C =2881 cm{sup -1}, with C/B = 3.65 (Mg{sup 2+} site) and Dq =2008 cm{sup -1}, B =790 cm{sup -1}, C =2949 cm{sup -1}, with C/B = 3.73 (Te{sup 6+} site). A cross-cutting comparative study of the variations in the crystal field splitting and the Racah parameters of the six-coordinated Mn{sup 4+} ion in a series of materials with the perovskite structure are presented. (orig.)

  19. Deformations of charge-density wave crystals under electric field

    Energy Technology Data Exchange (ETDEWEB)

    Pokrovskii, V.Ya. [Kotel' nikov Institute of Radioengineering and Electronics of RAS, Mokhovaya 11, 125009 Moscow (Russian Federation)], E-mail: pok@cplire.ru; Zybtsev, S.G.; Loginov, V.B. [Kotel' nikov Institute of Radioengineering and Electronics of RAS, Mokhovaya 11, 125009 Moscow (Russian Federation); Timofeev, V.N. [Baikov Institute of Metallurgy of RAS, Leninsky prosp. 49, 119991 Moscow (Russian Federation); Kolesov, D.V.; Yaminsky, I.V. [Advanced Technologies Center, Department of Physics, Moscow State University, Leninskie Gori, 119991 Moscow (Russian Federation); Gorlova, I.G. [Kotel' nikov Institute of Radioengineering and Electronics of RAS, Mokhovaya 11, 125009 Moscow (Russian Federation)

    2009-03-01

    We report the effects of electric field induced deformations of quasi one-dimensional conductors with charge-density wave (CDW). The most pronounced sort of deformation is torsional strain (TS). The TS is found to comprise two contributions. The features of the 1st-the larger one-are threshold hysteretic dependence on electric field and high relaxation time {tau}: For o-TaS{sub 3}{tau}{approx}10{sup -2} s at T=80 K and falls as exp(900 K/T) with increasing T. The 2nd contribution is linear in electric field and does not drop with frequency increase. The amplitude of this contribution falls abruptly with T approaching the Peierls transition temperature T{sub P} from below. Similar features of TS are demonstrated for other CDW compounds: (TaSe{sub 4}){sub 2}I, K{sub 0.3}MoO{sub 3} and NbS{sub 3} type II, for which T{sub P}{approx}360 K. We attribute the 1st and the 2nd contributions to large (hysteretic) and small (near-equilibrium) CDW deformations, respectively, likely-shear at the surface. The TS is observed also above T{sub P}: For TaS{sub 3} and (TaSe{sub 4}){sub 2}I typical torsional amplitude is 10{sup -1} deg./V in the resonance regimes, corresponding to the piezomodulus {approx}10{sup -9} m/V. A separate study of TS was performed at room temperature with AFM technique. Apart from this ('intrinsic') effect, we observe electrostatic contribution to the TS. In contrast to the intrinsic response, the electrostatic one is proportional to the potential either over the sample, or over an additional electrode ('gate') placed nearby, but not to the difference of potentials between the sample ends. It is typically 2 orders of magnitude less. The intrinsic TS reveals a new electromechanical effect at room temperature, presumably associated with the excitations of the pinned mode of the CDW fluctuations. Its observation opens prospects for application of quasi one-dimensional conductors as micro- and nano-actuators. Basing on the electrostatic

  20. Dependence of image flicker on dielectric anisotropy of liquid crystal in a fringe field switching liquid crystal cell

    Science.gov (United States)

    Oh, Seung-Won; Baek, Jong-Min; Kim, Jung-Wook; Yoon, Tae-Hoon

    2016-09-01

    Two types of image flicker, which are caused by the flexoelectric effect of liquid crystals (LCs), are observed when a fringe-field switching (FFS) LC cell is driven by a low frequency electric field. Static image flicker, observed because of the transmittance difference between neighboring frames, has been reported previously. On the other hand, research on dynamic image flicker has been minimal until now. Dynamic image flicker is noticeable because of the brief transmittance drop when the sign of the applied voltage is reversed. We investigated the dependence of the image flicker in an FFS LC cell on dielectric anisotropy of the LCs in terms of both the static and dynamic flicker. Experimental results show that small dielectric anisotropy of the LC can help suppress not only the static but also dynamic flicker for positive LCs. We found that both the static and dynamic flicker in negative LCs is less evident than in positive LCs.

  1. Electric Field-Controlled Crystallizing CaCO3 Nanostructures from Solution.

    Science.gov (United States)

    Qi, Jian Quan; Guo, Rui; Wang, Yu; Liu, Xuan Wen; Chan, Helen Lai Wah

    2016-12-01

    The role of electric field is investigated in determining the structure, morphology, and crystallographic characteristics of CaCO3 nanostructures crystallized from solution. It is found that the lattice structure and crystalline morphology of CaCO3 can be tailed by the electric field applied to the solution during its crystallization. The calcite structure with cubic-like morphology can be obtained generally without electric field, and the vaterite structure with the morphology of nanorod is formed under the high electric field. The vaterite nanorods can be piled up to the petaliform layers. Both the nanorod and the petaliform layer can have mesocrystal structures which are piled up by much fine units of the rods with the size of several nanometers. Beautiful rose-like nanoflowers can be self-arranged by the petaliform layers. These structures can have potential application as carrier for medicine to involve into metabolism of living cell.

  2. Fine splits of photon emission spectrum of hydrogen atom caused by transitions between different dressed states in intense high frequency laser field

    Institute of Scientific and Technical Information of China (English)

    Zhou Zhao-Yan; Yuan Jian-Min

    2008-01-01

    The photon emission spectrum of the hydrogen atoms in an intense high-frequency laser pulse is simulated by using one-dimensional soft Coulomb potential. Regular fine structures appear on the two sides of both the odd and even multiples of photon energy of the laser field besides the ordinary odd harmonic peaks. It is proved that the splits of the fine structures are responsible for hyper-Raman lines and the energy spacing between the odd harmonic lines is equal to the difference in energy between the eigenstates with the same parity of the time averaged Krameters-Henneberger (KH) potential. By analysing the features of the fine structures, we also verify that the so-called even order harmonics under the stabilization condition are indeed hyper-Raman lines caused by the transitions between the dressed atomic states with different values of parity.

  3. Design of Gd(III)-based magnetic resonance imaging contrast agents: static and transient zero-field splitting contributions to the electronic relaxation and their impact on relaxivity.

    Science.gov (United States)

    Benmelouka, Meriem; Borel, Alain; Moriggi, Loick; Helm, Lothar; Merbach, André E

    2007-02-01

    A multiple-frequency (9.4-325 GHz) and variable-temperature (276-320 K) electron paramagnetic resonance (EPR) study on low molecular weight gadolinium(III) complexes for potential use as magnetic resonance imaging (MRI) contrast agents has been performed. Peak-to-peak linewidths Delta Hpp and central magnetic fields have been analyzed within the Redfield approximation taking into account the static zero-field splitting (ZFS) up to the sixth order and the transient ZFS up to the second order. Longitudinal electronic relaxation is dominated by the static ZFS contribution at low magnetic fields (B 1.5 T). Whereas the static ZFS clearly depends on the nature of the chelating ligand, the transient ZFS does not. For the relatively fast rotating molecules studied water proton relaxivity is mainly limited by the fast rotation and electronic relaxation has only a marked influence at frequencies below 30 MHz. From our EPR results we can conclude that electronic relaxation will have no influence on the efficiency of Gd(III)-based MRI contrast agents designed for studies at very high magnetic fields (B > 3T).

  4. Crystal fields of dilute Tb, Dy, or Er in Sc obtained by magnetization measurements

    DEFF Research Database (Denmark)

    Høg, J.; Touborg, P.

    1976-01-01

    Crystal-field parameters for dilute Sc-Tb, Sc-Dy, and Sc-Er alloys have been obtained by fitting theoretical expressions to the experimentally measured paramagnetic susceptibility. The initial susceptibility was measured and corrected for the effects of ordering at the lowest temperatures in the ...

  5. Tuning the Colloidal Crystal Structure of Magnetic Particles by External Field

    NARCIS (Netherlands)

    Pal, Antara; Malik, Vikash; He, Le; Erne, Ben H.; Yin, Yadong; Kegel, Willem K.; Petukhov, A. V.

    2015-01-01

    Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-a

  6. Ambipolar Cu- and Fe-phthalocyanine single-crystal field-effect transistors

    NARCIS (Netherlands)

    De Boer, R.W.I.; Stassen, A.F.; Craciun, M.F.; Mulder, C.L.; Molinari, A.; Rogge, S.; Morpurgo, A.F.

    2005-01-01

    We report the observation of ambipolar transport in field-effect transistors fabricated on single crystals of copper- and iron-phthalocyanine, using gold as a high work-function metal for the fabrication of source and drain electrodes. In these devices, the room-temperature mobility of holes reaches

  7. Reproducible low contact resistance in rubrene single-crystal field-effect transistors with nickel electrodes

    NARCIS (Netherlands)

    Hulea, I.N.; Russo, S.; Molinari, A.; Morpurgo, A.F.

    2006-01-01

    We have investigated the contact resistance of rubrene single-crystal field-effect transistors (FETs) with nickel electrodes by performing scaling experiments on devices with channel length ranging from 200 nm up to 300 μm. We find that the contact resistance can be as low as 100 Ω cm with narrowly

  8. Bias-dependent contact resistance in rubrene single-crystal field-effect transistors

    NARCIS (Netherlands)

    Molinari, A.; Gutiérrez, I.; Hulea, I.N.; Russo, S.; Morpurgo, A.F.

    2007-01-01

    The authors report a systematic study of the bias-dependent contact resistance in rubrene single-crystal field-effect transistors with Ni, Co, Cu, Au, and Pt electrodes. They show that the reproducibility in the values of contact resistance strongly depends on the metal, ranging from a factor of 2 f

  9. Ambipolar Cu- and Fe-phthalocyanine single-crystal field-effect transistors

    NARCIS (Netherlands)

    De Boer, R.W.I.; Stassen, A.F.; Craciun, M.F.; Mulder, C.L.; Molinari, A.; Rogge, S.; Morpurgo, A.F.

    2005-01-01

    We report the observation of ambipolar transport in field-effect transistors fabricated on single crystals of copper- and iron-phthalocyanine, using gold as a high work-function metal for the fabrication of source and drain electrodes. In these devices, the room-temperature mobility of holes reaches

  10. Effect of electrical field on crystallization and ferroelectric properties of Ge:Sb:Te films

    Energy Technology Data Exchange (ETDEWEB)

    Gervacio Arciniega, J.J.; Prokhorov, E.; Espinoza Beltran, F.J.; Trapaga Martinez, L.G. [CINVESTAV, Unidad Queretaro (Mexico); Gonzalez-Hernandez, J. [Centro de Investigacion en Materiales Avanzados, S.C. and Laboratorio Nacional de Nanotecnologia, Chihuahua (Mexico)

    2011-11-15

    In this work impedance spectroscopy has been used to investigate of the NaCl type-hexagonal transition in stoichiometric Ge{sub 2}Sb{sub 2}Te{sub 5} and in non-stoichiometric (Ge{sub 24}Sb{sub 15}Te{sub 61}) films. The temperature dependence of capacitance in all films shows an abrupt change (about 4-6 times) at the temperature corresponding to the end of the NaCl type-hexagonal transition. Additional, impedance measurements were carried out in films which have been crystallized with an external DC electric field. Comparing the results in the films crystallized with and without the external electric field, it is observed that in films crystallized with an external electric field, the capacitance increases during the NaCl type-hexagonal transition for about 9-15 times and that the piezoresponse force microscopy measurements have shown ferroelectric domains in the NaCl type phase. External electrical field changes significantly the onset of amorphous-NaCl type crystallization temperature which could be related with an increase in atomic diffusion, promoting the growth of the crystalline phase. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Scaling of crystal field parameters between Pd 2REIn and Pd 2RESn

    Science.gov (United States)

    Babateen, M.; Neumann, K.-U.; Ziebeck, K. R. A.

    1995-02-01

    Experimentally it is found that crystal field (CF) parameters between the same rare earth compounds in the alloy series Pd 2REIn and Pd 2RESn (RE = rare earth element) exhibit scaling properties. A phenomenological model is put forward to explain this observation.

  12. Near-field imaging of out-of-plane light scattering in photonic crystal slabs

    DEFF Research Database (Denmark)

    Volkov, Valentyn; Bozhevolnyi, Sergey; Taillaert, Dirk

    2003-01-01

    A collection scanning near-field optical microscope (SNOM) is used to image the propagating of light at telecommunication wavelengths (1520-1570 nm) along photonic crystal (PC) slabs, which combine slab waveguides with in-plane PCs consisting of one- and two-dimensional gratings. The efficient out...

  13. Spin splitting generated in a Y-shaped semiconductor nanostructure with a quantum point contact

    Energy Technology Data Exchange (ETDEWEB)

    Wójcik, P., E-mail: pawel.wojcik@fis.agh.edu.pl; Adamowski, J., E-mail: janusz.adamowski@fis.agh.edu.pl; Wołoszyn, M.; Spisak, B. J. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, Kraków (Poland)

    2015-07-07

    We have studied the spin splitting of the current in the Y-shaped semiconductor nanostructure with a quantum point contact (QPC) in a perpendicular magnetic field. Our calculations show that the appropriate tuning of the QPC potential and the external magnetic field leads to an almost perfect separation of the spin-polarized currents: electrons with opposite spins flow out through different output branches. The spin splitting results from the joint effect of the QPC, the spin Zeeman splitting, and the electron transport through the edge states formed in the nanowire at the sufficiently high magnetic field. The Y-shaped nanostructure can be used to split the unpolarized current into two spin currents with opposite spins as well as to detect the flow of the spin current. We have found that the separation of the spin currents is only slightly affected by the Rashba spin-orbit coupling. The spin-splitter device is an analogue of the optical device—the birefractive crystal that splits the unpolarized light into two beams with perpendicular polarizations. In the magnetic-field range, in which the current is carried through the edges states, the spin splitting is robust against the spin-independent scattering. This feature opens up a possibility of the application of the Y-shaped nanostructure as a non-ballistic spin-splitter device in spintronics.

  14. Magnetic-Field-Induced Weak Order in Nematic Liquid Crystals Formed by Biaxial Molecules

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhi-Dong; ZHANG De-Xian; SUN Yu-Bao

    2000-01-01

    Nematic liquid crystal system of interacting biaxial particles via dispersion forces is studied. The molecular orienting potential form in a magnetic field is given for the first time. Weakly ordered isotropic phase is treated in the two-particle cluster approximation. Taking account of the molecular biaxiality, it is found that the ratio of the lowest supercooling temperature T* to the nematic-isotropic phase transition temperature TC approaches the observed value, and the validity of the mean field theory is clarified.

  15. Bridging the terahertz near-field and far-field observations of liquid crystal based metamaterial absorbers

    Science.gov (United States)

    Wang, Lei; Ge, Shijun; Chen, Zhaoxian; Hu, Wei; Lu, Yanqing

    2016-09-01

    Metamaterial-based absorbers play a significant role in applications ranging from energy harvesting and thermal emitters to sensors and imaging devices. The middle dielectric layer of conventional metamaterial absorbers has always been solid. Researchers could not detect the near field distribution in this layer or utilize it effectively. Here, we use anisotropic liquid crystal as the dielectric layer to realize electrically fast tunable terahertz metamaterial absorbers. We demonstrate strong, position-dependent terahertz near-field enhancement with sub-wavelength resolution inside the metamaterial absorber. We measure the terahertz far-field absorption as the driving voltage increases. By combining experimental results with liquid crystal simulations, we verify the near-field distribution in the middle layer indirectly and bridge the near-field and far-field observations. Our work opens new opportunities for creating high-performance, fast, tunable, terahertz metamaterial devices that can be applied in biological imaging and sensing. Project supported by the National Basic Research Program of China (Grant No. 2012CB921803), the National Natural Science Foundation of China (Grants Nos. 61225026, 61490714, 11304151, and 61435008), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20150845 and 15KJB140004), the Open Foundation Project of National Laboratory of Solid State Microstructures, China (Grant No. M28003), and the Research Center of Optical Communications Engineering & Technology, Jiangsu Province, China.

  16. Split Q-balls

    Science.gov (United States)

    Bazeia, D.; Losano, L.; Marques, M. A.; Menezes, R.

    2017-02-01

    We investigate the presence of non-topological solutions of the Q-ball type in (1 , 1) spacetime dimensions. The model engenders the global U (1) symmetry and is of the k-field type, since it contains a new term, of the fourth-order power in the derivative of the complex scalar field. It supports analytical solution of the Q-ball type which is stable quantum mechanically. The new solution engenders an interesting behavior, with the charge and energy densities unveiling a splitting profile.

  17. Effect of non-uniform magnetic field on crystal growth by floating-Zone method in microgravity

    Institute of Scientific and Technical Information of China (English)

    LI; Kai(

    2001-01-01

    [1]Markov, E. V., Antropov, V. Yu, Biryukov, V. M. et al., Space materials for microelectronics, in Proceedings of the Joint Xth European and VIth Russian Symposium on Physical Sciences in Microgravity, St. Petersburg, Russia (eds. Av-duyevsky, V. S., Polezhaev, V. I.), Moscow: RAS, 1997, Vol. 2, 11-20.[2]Croll, A., Dold, P., Benz, K. W., Segregation in Si floating-zone crystals grown under microgravity and in a magnetic field, J. Crystal Growth, 1994, 137: 95-101.[3]Leon de, N., Guldberg, J., Sailing, J. , Growth of homogeneous high resistivity FZ silicon crystals under magnetic field bias, J. Crystal Growth, 1981, 55: 406-408.[4]Robertson, D. G., O' connor Jr., D. J., Magnetic field effects on float-zone Si crystal growth: strong axial fields, J. Crystal Growth, 1986, 76: 111-122.[5]Series, R. W., Hurle, D. T. J., The use of magnetic field in semiconductor crystal growth, J. Crystal Growth, 1991, 113:305-328.[6]Lan, C. W. , Effect of axisymmetric magnetic fields on radial dopant segregation of floating-zone silicon growth in a mirror fur-nace, J. Crystal Growth, 1996, 169: 269-278.[7]Li, K., Hu, W. R. , Numerical simulation of magnetic field design for damping thermocapillary convection in a floating half zone, J. Crystal Growth, 2001, 222: 677-684.[8]Li. K., Hu, W. R., Magnetic design for crystal growth, 3rd International Workshop on Modeling in Crystal Growth, New York, USA, 2000, to be published in J. Crystal Growth.[9]Patankar, S. V., Advanced Computational Heat Transfer and Fluid Flow, Graduate Student Course 8352 of Mechanical Engi-neering Department at Univ. of Minnesota, USA.

  18. Electrical properties and electrical field in depletion layer for CZT crystals

    Institute of Scientific and Technical Information of China (English)

    LI Qiang; JIE Wan-qi; FU Li; YANG Ge; ZHA Gang-qiang; WANG Tao; BAI Xu-xu

    2006-01-01

    Current—voltage (I—V) and capacitance-voltage (C—V) characteristics of Au/p-CZT contacts with different surface treatments on cadmium zinc telluride (CZT) wafer's surface were measured with Agilent 4339B high resistance meter and Agilent 4294A precision impedance analyzer,respectively. The Schottky barrier height was 0.85±0.05,0.96±0.05 eV for non-passivated and passivated CZT crystals by I—V measurement. By C—V measurement,the Schottky barrier height was 1.39±0.05,1.51±0.05 eV for non-passivated and passivated CZT crystals. The results show that the passivation treatment can increase the barrier height of the Au/p-CZT contact and decrease the leakage current. The main reason is that the higher barrier height of Au/p-CZT contacts can decrease the possibility for electrons to pass through the native TeO2 film. Most of the applied voltage appears on the depleted layer and there is only a negligible voltage drops across the nearly undepleted region. Furthermore,the electric field in the depleted layer is not uniform and can be calculated by the depletion approximation. The maximum electric field of CZT crystals is Em1=133 V/cm at x=0 for non-passivated CZT crystal and Em2=55 V/cm for passivated CZT crystal,respectively.

  19. Patterning technology for solution-processed organic crystal field-effect transistors

    Science.gov (United States)

    Li, Yun; Sun, Huabin; Shi, Yi; Tsukagoshi, Kazuhito

    2014-04-01

    Organic field-effect transistors (OFETs) are fundamental building blocks for various state-of-the-art electronic devices. Solution-processed organic crystals are appreciable materials for these applications because they facilitate large-scale, low-cost fabrication of devices with high performance. Patterning organic crystal transistors into well-defined geometric features is necessary to develop these crystals into practical semiconductors. This review provides an update on recent development in patterning technology for solution-processed organic crystals and their applications in field-effect transistors. Typical demonstrations are discussed and examined. In particular, our latest research progress on the spin-coating technique from mixture solutions is presented as a promising method to efficiently produce large organic semiconducting crystals on various substrates for high-performance OFETs. This solution-based process also has other excellent advantages, such as phase separation for self-assembled interfaces via one-step spin-coating, self-flattening of rough interfaces, and in situ purification that eliminates the impurity influences. Furthermore, recommendations for future perspectives are presented, and key issues for further development are discussed.

  20. Patterning technology for solution-processed organic crystal field-effect transistors

    Directory of Open Access Journals (Sweden)

    Yun Li

    2014-04-01

    Full Text Available Organic field-effect transistors (OFETs are fundamental building blocks for various state-of-the-art electronic devices. Solution-processed organic crystals are appreciable materials for these applications because they facilitate large-scale, low-cost fabrication of devices with high performance. Patterning organic crystal transistors into well-defined geometric features is necessary to develop these crystals into practical semiconductors. This review provides an update on recent development in patterning technology for solution-processed organic crystals and their applications in field-effect transistors. Typical demonstrations are discussed and examined. In particular, our latest research progress on the spin-coating technique from mixture solutions is presented as a promising method to efficiently produce large organic semiconducting crystals on various substrates for high-performance OFETs. This solution-based process also has other excellent advantages, such as phase separation for self-assembled interfaces via one-step spin-coating, self-flattening of rough interfaces, and in situ purification that eliminates the impurity influences. Furthermore, recommendations for future perspectives are presented, and key issues for further development are discussed.

  1. Ionization of Atoms and the Thomas-Fermi Model for the Electric Field in Crystal Planar Channels

    Institute of Scientific and Technical Information of China (English)

    LIU Ying-Tai; ZHANG Qi-Ren; GAO Chun-Yuan

    2002-01-01

    The electric field in the crystal planar channels is studied by the Thomas Fermi method. The Thomas-Fermi equation and the corresponding boundary conditions are derived for the crystal planar channels. The numericalsolution for the electric field in the channels between (110) planes of the single crystal silicon and the critical angles ofchannelling protons in them are shown. Reasonable agreements with the experimental data are obtained. The resultsshow that the Thomas-Fermi method for the crystal works well in this study, and a microscopic research of the channelelectric field with the contribution of all atoms and the atomic ionization being taken into account is practical.

  2. Electro-optical switching by liquid-crystal controlled metasurfaces

    CERN Document Server

    Decker, Manuel; Minovich, Alexander; Staude, Isabelle; Miroshnichenko, Andrey E; Chigrin, Dmitry; Neshev, Dragomir N; Jagadish, Chennupati; Kivshar, Yuri S

    2013-01-01

    We study the optical response of a metamaterial surface created by a lattice of split-ring resonators covered with a nematic liquid crystal and demonstrate millisecond timescale switching between electric and magnetic resonances of the metasurface. This is achieved due to a high sensitivity of liquid-crystal molecular reorientation to the symmetry of the metasurface as well as to the presence of a bias electric field. Our experiments are complemented by numerical simulations of the liquid-crystal reorientation.

  3. Crystal-field spectra of 3d super n impurities in II-VI and III-V compound semiconductors.

    Science.gov (United States)

    Allen, J. W.; Baranowski, J. M.; Pearson, G. L.

    1967-01-01

    Impurity crystal-field spectra in II-VI and III- V compound semiconductors used to predict unexplored systems spectra impurity crystal-field spectra in II-VI and III-V compound semiconductors used to predict unexplored systems spectra

  4. The mechanism of paramagnetic NMR relaxation produced by Mn(II): role of orthorhombic and fourth-order zero field splitting terms.

    Science.gov (United States)

    Sharp, Robert

    2008-10-14

    Mn(II) is a spin-5/2 paramagnetic ion that mediates a characteristically large NMR paramagnetic relaxation enhancement (NMR-PRE) of nuclear spins in solution. In the range of high magnetic field strengths (above about 0.3 T), where the electronic Zeeman interaction provides the largest term of the electron spin Hamiltonian, NMR relaxation mechanism is well understood. In the lower field range, the physical picture is more complex because of the presence in the spin Hamiltonian of zero field splitting (ZFS) terms that are comparable to or greater than the Zeeman term. This work describes a systematic study of the relaxation mechanism in the low field range, particularly aspects involving the dependence of NMR-PRE on the orthorhombic (E) and fourth-order (a(q)(4), q=0,2,4) ZFS tensor components. It is shown that the fourfold (a(4)(4)) and twofold (a(2)(4)) fourth-order components exert large orientation-dependent influences on the NMR-PRE. Thus, fourth-order terms with magnitudes equal to only a few percent of the quadratic ZFS terms (D,E) produce large changes in the shape of the magnetic field profile of the PRE. Effects arising from the orthorhombic quadratic ZFS term (E) are much smaller than those of the fourth-order terms and can in most cases be neglected. However, effects due to a(4)(4) and a(2)(4) need to be included in simulations of low field data.

  5. Wide-field-of-view narrow-band spectral filters based on photonic crystal nanocavities.

    Science.gov (United States)

    Nakagawa, Wataru; Sun, Pang-Chen; Chen, Chyong-Hua; Fainman, Yeshaiahu

    2002-02-01

    We describe a novel approach to implementing wide-field-of-view narrow-band spectral filters, using an array of resonant nanocavities consisting of periodic defects in a two-dimensional three-material photonic-crystal nanostructure. We analyze the transmissivity of this type of filter for a range of wavelengths and in-plane incidence angles as a function of the defect's refractive index, the number of layers in the photonic-crystal reflectors, and the period of the defects and find that this structure diminishes the angular sensitivity of the resonance condition relative to that of a standard multilayer filter.

  6. Optical study of the molecular alignment in a nematic liquid crystal in an oblique magnetic field

    OpenAIRE

    Oldano, C.; Miraldi, E.; Strigazzi, A.; Taverna Valabrega, P.; Trossi, L.

    1984-01-01

    The light intensity I transmitted through a homeotropically oriented nematic liquid crystal slab held between crossed polarizers, as a function of the angle θH of an applied magnetic field, is calculated for oblique light incidence. The presence of singular points in the I vs. θ H curve which are related to the elastic constants of the liquid crystal is demonstrated One of these points, found here for the first time, for small angles of incidence depends only on the ratio K33/Χ a, and allows ...

  7. Creating physically-based three-dimensional microstructures: Bridging phase-field and crystal plasticity models.

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Hojun [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Owen, Steven J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Abdeljawad, Fadi F. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Hanks, Byron [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Battaile, Corbett Chandler [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    In order to better incorporate microstructures in continuum scale models, we use a novel finite element (FE) meshing technique to generate three-dimensional polycrystalline aggregates from a phase field grain growth model of grain microstructures. The proposed meshing technique creates hexahedral FE meshes that capture smooth interfaces between adjacent grains. Three dimensional realizations of grain microstructures from the phase field model are used in crystal plasticity-finite element (CP-FE) simulations of polycrystalline a -iron. We show that the interface conformal meshes significantly reduce artificial stress localizations in voxelated meshes that exhibit the so-called "wedding cake" interfaces. This framework provides a direct link between two mesoscale models - phase field and crystal plasticity - and for the first time allows mechanics simulations of polycrystalline materials using three-dimensional hexahedral finite element meshes with realistic topological features.

  8. Neutron investigations of magnetic properties of crystal substances with use of a pulsed magnetic field

    CERN Document Server

    Nitts, V V

    2001-01-01

    Bases for neutron researches of magnetic properties of crystal substances with use of a pulsed magnetic field and analysis of possible application of various neutron sources in this area are submitted. The review of the most interesting physical results is presented. Main investigations on pulsed reactors of JINR are researches on kinetics of the first order reorientational phase transitions induced in single crystals, and also measurements of antiferromagnetic ordering induced by an external magnetic field. Magnetic phase transitions, induced by a field up to 160 kOe in several magnetic ordering substances, were studied in KEK (Japan). Experiment on observation of spin-flop transition in MnF sub 2 was carried out on TRIGA-reactor in a mode of single flashes of power

  9. Rectangular split-ring resonators with single-split and two-splits under different excitations at microwave frequencies

    Directory of Open Access Journals (Sweden)

    S. Zahertar

    2015-11-01

    Full Text Available In this work, transmission characteristics of rectangular split-ring resonators with single-split and two-splits are analyzed at microwave frequencies. The resonators are coupled with monopole antennas for excitation. The scattering parameters of the devices are investigated under different polarizations of E and H fields. The magnetic resonances induced by E and H fields are identified and the differences in the behavior of the resonators due to orientations of the fields are explained based on simulation and experimental results. The addition of the second split of the device is investigated considering different configurations of the excitation vectors. It is demonstrated that the single-split and the two-splits resonators exhibit identical transmission characteristics for a certain excitation configuration as verified with simulations and experiments. The presented resonators can effectively function as frequency selective media for varying excitation conditions.

  10. Resistive memory effects in BiFeO3 single crystals controlled by transverse electric fields

    Science.gov (United States)

    Kawachi, S.; Kuroe, H.; Ito, T.; Miyake, A.; Tokunaga, M.

    2016-04-01

    The effects of electric fields perpendicular to the c-axis of the trigonal cell in single crystals of BiFeO3 are investigated through magnetization and resistance measurements. Magnetization and resistance exhibit hysteretic changes under applied electric fields, which can be ascribed to the reorientation of the magnetoelectric domains. Samples are repetitively switched between high- and low-resistance states by changing the polarity of the applied electric fields over 20 000 cycles at room temperature. These results demonstrate the potential of BiFeO3 for use in non-volatile memory devices.

  11. Molecular Field Calculation of Magnetization on NdRh2Ge2 Single Crystal

    Directory of Open Access Journals (Sweden)

    A. Himori

    2008-01-01

    Full Text Available Calculation of magnetization of the ternary single crystal compound NdRh2Ge2 has been carried out by using the wave-like molecular field model to explain the complex magnetic behavior. The field-induced magnetic structures having the propagation vectors, 2=(0,0,39/40, 3=(0,0,35/40, 4=(0,0,31/40, and 5=(0,0,0/40 (= the field-induced ferromagnetic phase were proposed. Calculation on the basis of these structures and the antiferromagnetic phase with 1=(0,0,1 well reproduces the experimental magnetization processes and - magnetic phase diagram.

  12. Optical near-field microscopy of light focusing through a photonic crystal flat lens.

    Science.gov (United States)

    Fabre, Nathalie; Lalouat, Loïc; Cluzel, Benoit; Mélique, Xavier; Lippens, Didier; de Fornel, Frédérique; Vanbésien, Olivier

    2008-08-15

    We report here the direct observation by using a scanning near-field microscopy technique of the light focusing through a photonic crystal flat lens designed and fabricated to operate at optical frequencies. The lens is fabricated using a III-V semiconductor slab, and we directly visualize the propagation of the electromagnetic waves by using a scanning near-field optical microscope. We directly evidence spatially, as well as spectrally, the focusing operating regime of the lens. At last, in light of the experimental scanning near-field optical microscope pictures, we discuss the lens ability to focus light at a subwavelength scale.

  13. Enhancement of local electromagnetic fields in plasmonic crystals of coaxial metallic nanostructures

    Science.gov (United States)

    Iwanaga, Masanobu; Ikeda, Naoki; Sugimoto, Yoshimasa

    2012-01-01

    We have experimentally and numerically examined resonant modes in plasmonic crystals (PlCs) of coaxial metallic nanostructures. Resonance enhancements of local electromagnetic (EM) fields were evaluated quantitatively. We clarified that a local mode induced in the coaxial metallic structure shows the most significant field enhancement. The enhancement factors are comprehensively discussed by comparison with other PlCs, indicating that the coaxial PlC provides a locally intense electric field and EM power flux in the annular slit of 50-nm metallic gaps.

  14. A study of dark resonance splitting for the D 1 line of 87Rb in strong magnetic fields

    Science.gov (United States)

    Sargsyan, A.; Mirzoyan, R.; Sarkisyan, D.

    2012-11-01

    The process of electromagnetically induced transparency (EIT) is studied using an extremely thin cell with thickness of a vapor column of rubidium atoms L = 794 nm. Wavelengths of resonant laser beams λ ≈ 794 nm. Results of the study of behavior of the EIT resonance (which is also called the "dark" resonance) formed in the Л system of the D 1 line of 87Rb atoms in strong magnetic fields up to 1700 G (0.17 T) are reported for the first time. Three dark resonances are recorded in magnetic fields with induction B 650 G, and only one dark resonance is retained at B > 1200 G. A method of the formation of a dark resonance at a given frequency is demonstrated that will allow, under the corresponding conditions, the formation of a dark resonance also at B > 0.2 T. The experimental results are well described by the known theoretical models. Practical applications of these results are indicated.

  15. Near-Field Optical Microscopy of Defects in Cholesteric Oligomeric Liquid Crystal Films

    Energy Technology Data Exchange (ETDEWEB)

    Lukishova, S.G.; Schmid, A.W.

    2006-08-18

    This paper describes formation of 2-D hexagonal structures with a periodicity ~0.5-0.8 um in the defects of thin films of cholesteric oligomeric liquid crystals prepared by the evaporation of the solvent from the oligomer solution on the substrate. These regular arrays were observed by scanning near-field optical and concurrent atomic force microscopy. The mechanisms considered are both Benard-Marangoni and buoyancy conventions induced by solvent evaporation and air-bubble creation around the condensed water droplets from the air during evaporative cooling. Hexagonal structures prepared by this method can be used in photonic devices for emission enhancement, for instance, in liquid crystal lasers and single photon sources with oligomeric liquid crystal hosts.

  16. Phase-field simulations of faceted Ge/Si-crystal arrays, merging into a suspended film

    Science.gov (United States)

    Salvalaglio, Marco; Bergamaschini, Roberto; Backofen, Rainer; Voigt, Axel; Montalenti, Francesco; Miglio, Leo

    2017-01-01

    We simulate the morphological evolution of Ge microcrystals, grown out-of-equilibrium on deeply patterned Si substrates, as resulting from surface diffusion driven by the tendency toward the minimization of the surface energy. In particular, we report three-dimensional phase-field simulations accounting for the realistic surface energy anisotropy of Ge/Si crystals. In Salvalaglio et al. (2015) [10] it has been shown both by experiments and simulations that annealing of closely spaced crystals leads to a coalescence process with the formation of a suspended film. However, this was explained only by considering an isotropic surface energy. Here, we extend such a study by showing first the morphological changes of faceted isolated crystals. Then, the evolution of dense arrays is considered, describing their coalescence along with the evolution of facets. Combined with the previous results without anisotropy in the surface energy, this work allows us to confirm and assess the key features of the coalescence process.

  17. Role of internal demagnetizing field for the dynamics of a surface-modulated magnonic crystal

    Science.gov (United States)

    Langer, M.; Röder, F.; Gallardo, R. A.; Schneider, T.; Stienen, S.; Gatel, C.; Hübner, R.; Bischoff, L.; Lenz, K.; Lindner, J.; Landeros, P.; Fassbender, J.

    2017-05-01

    This work aims to demonstrate and understand the key role of local demagnetizing fields in hybrid structures consisting of a continuous thin film with a stripe modulation on top. To understand the complex spin dynamics of these structures, the magnonic crystal was reconstructed in two different ways—performing micromagnetic simulations based on the structural shape as well as based on the internal demagnetizing field, which both are mapped on the nanoscale using electron holography. The simulations yield the frequency-field dependence as well as the angular dependence revealing the governing role of the internal field landscape around the backward-volume geometry. Simple rules for the propagation vector and the mode localization are formulated in order to explain the calculated mode profiles. Treating internal demagnetizing fields equivalent to anisotropies, the complex angle-dependent spin-wave behavior is described for an in-plane rotation of the external field.

  18. Pinning features of the magnetic flux trapped by YBCO single crystals in weak constant magnetic fields

    Science.gov (United States)

    Monarkha, V. Yu.; Paschenko, V. A.; Timofeev, V. P.

    2013-02-01

    The dynamics of Abrikosov vortices and their bundles was experimentally investigated in weak constant magnetic fields, in the range of Earth's magnetic field. Characteristics of the isothermal magnetization relaxation in YBCO single-crystal samples with strong pinning centers were studied for different sample-field orientation. The obtained values of normalized relaxation rate S allowed us to estimate the effective pinning potential U in the bulk of the YBCO sample and its temperature dependence, as well as the critical current density Jc. A comparison between the data obtained and the results of similar measurements in significantly higher magnetic fields was performed. To compare different techniques for evaluation of Jc, the magnetization loop measurements M(H), which relate the loop width to the critical current, were carried out. These measurements provided important parameters of the samples under study (penetration field Hp and first critical field Hc1), which involve the geometrical configuration of the samples.

  19. Thermally induced photon splitting

    CERN Document Server

    Elmfors, P; Elmfors, Per; Skagerstam, Bo-Sture

    1998-01-01

    We calculate thermal corrections to the non-linear QED effective action for low-energy photon interactions in a background electromagnetic field. The high-temperature expansion shows that at $T \\gg m$ the vacuum contribution is exactly cancelled to all orders in the external field except for a non-trivial two-point function contribution. The high-temperature expansion derived reveals a remarkable cancellation of infrared sensitive contributions. As a result photon-splitting in the presence of a magnetic field is suppressed in the presence of an electron-positron QED-plasma at very high temperatures. In a cold and dense plasma a similar suppression takes place. At the same time Compton scattering dominates for weak fields and the suppression is rarely important in physical situations.

  20. Effect of magnetic field on the wave dispersion relation in three-dimensional dusty plasma crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yang Xuefeng [School of Mathematical Sciences, Dalian University of Technology, Dalian 116024 (China); Wang Zhengxiong [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)

    2012-07-15

    Three-dimensional plasma crystals under microgravity condition are investigated by taking into account an external magnetic field. The wave dispersion relations of dust lattice modes in the body centered cubic (bcc) and the face centered cubic (fcc) plasma crystals are obtained explicitly when the magnetic field is perpendicular to the wave motion. The wave dispersion relations of dust lattice modes in the bcc and fcc plasma crystals are calculated numerically when the magnetic field is in an arbitrary direction. The numerical results show that one longitudinal mode and two transverse modes are coupled due to the Lorentz force in the magnetic field. Moreover, three wave modes, i.e., the high frequency phonon mode, the low frequency phonon mode, and the optical mode, are obtained. The optical mode and at least one phonon mode are hybrid modes. When the magnetic field is neither parallel nor perpendicular to the primitive wave motion, all the three wave modes are hybrid modes and do not have any intersection points. It is also found that with increasing the magnetic field strength, the frequency of the optical mode increases and has a cutoff at the cyclotron frequency of the dust particles in the limit of long wavelength, and the mode mixings for both the optical mode and the high frequency phonon mode increase. The acoustic velocity of the low frequency phonon mode is zero. In addition, the acoustic velocity of the high frequency phonon mode depends on the angle of the magnetic field and the wave motion but does not depend on the magnetic field strength.

  1. Influence of electromagnetic field intensity on the metastable zone width of CaCO3 crystallization in circulating water

    Science.gov (United States)

    Wang, Jianguo; Liang, Yandong; Chen, Si

    2016-09-01

    In this study, changes in the metastable zone width of CaCO3 crystallization was determined through conductivity titration by altering electromagnetic field parameters applied to the circulating water system. The critical conductivity value and metastable zone curves of CaCO3 crystallization were determined under different solution concentrations and electromagnetic field intensities. Experimental results indicate that the effect of the electromagnetic field intensity on the critical conductivity value intensifies with the increase of solution concentration. Moreover, the metastable zone width of CaCO3 crystallization increases with the increase of electromagnetic field intensity within 200 Gs, thereby prolonging the induction period of nucleation.

  2. Milestone in the History of Field-Effect Liquid Crystal Displays and Materials

    Science.gov (United States)

    Schadt, Martin

    2009-03-01

    The history of digital electronics would have been very different without the invention of field-effect liquid crystal displays (LCDs) in 1970 and their sophisticated development and implementation into numerous products. Transmissive and reflective LCDs have become a key interface between man and machine. After almost 40 years of interdisciplinary R+D and engineering, today's LCDs enable virtually all display applications, including high definition television. Field-effect LCDs are characterized by flat design, low weight, low driving voltage, design flexibility, compatibility with silicon-on-glass and very low power consumption, especially in reflection. Their polarization-sensitive layer concept is the basis for sandwiching and integration of optical and electronic thin-film functions. The liquid crystal technology has become a fast growing industry over the past 38 years, today surpassing 100 billion, with many spin-offs into new areas. Prerequisite for field-effect LCDs and their large diversification potential is the unique self-organization of liquid crystals. New applications beyond displays based on self-organisation, smart boundary alignment, dedicated liquid crystalline materials and the ability of LCs to respond to electromagnetic fields, including light, are being developed. Examples for new applications are LC polymer thin-film optics, or synergies between LCDs and solid state back-lighting, such as inorganic and organic light emitting diodes (LEDs/OLEDs).

  3. Neutron diffraction investigations of zero-field and field-induced magnetic structures of DyNiSn single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Murogaki, K. [Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)]. E-mail: murogaki@fiberbit.net; Kawano, S. [Research Reactor Institute, Kyoto University, Osaka 590-0494 (Japan); Andoh, Y. [Faculty of Regional Sciences, Tottori University, Tottori 680-8551 (Japan); Takahashi, M. [Institute of Materials Science, University of Tsukuba, Ibaraki 305-8573 (Japan); Kurisu, M. [Japan Advanced Institute of Science and Technology, Ishikawa 923-1292 (Japan); Nakamoto, G. [Japan Advanced Institute of Science and Technology, Ishikawa 923-1292 (Japan); Anh, D.T. Kim [Japan Advanced Institute of Science and Technology, Ishikawa 923-1292 (Japan); Tsutaoka, T. [Graduate School of Education, Hiroshima University, Hiroshima 739-8524 (Japan)

    2006-02-09

    Single crystal neutron diffraction studies have been performed on the rare-earth ternary compound, DyNiSn. This crystal exhibits an incommensurate magnetic structure expressed by the propagation vector, Q = (0.662 0.352 0) with its third harmonics at low temperatures. In an external magnetic field applied along the c-axis DyNiSn shows incommensurate modulation with Q = (1 0.315 0) at 1.6 K, while along the easy magnetization direction of the b-axis a commensurate modulation with Q = (2/3 0 0) develops at 2 K. The results along the b-axis are fully consistent with the magnetization curve.

  4. First principle simulation of the temperature dependent magnetic circular dichroism of a trinuclear copper complex in the presence of zero field splitting.

    Science.gov (United States)

    Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

    2011-09-22

    We present a test of a recently developed density functional theory (DFT) based methodology for the calculation of magnetic circular dichroism (MCD) spectra in the presence of zero-field splitting (ZFS). The absorption and MCD spectra of the trinuclear copper complex μ(3)O ([Cu(3)(L)(μ(3)-O)](4+)), which models the native intermediate produced in the catalytic cycle of the multicopper oxidases, have been simulated from first principle within the framework of adiabatic time dependent density functional theory. The effects of the ZFS of the quartet (4)A(2) ground state on the theoretical MCD spectrum of μ(3)O have been analyzed. The simulated spectra are consistent with the experimental ones. The theoretical assignments of the MCD spectra are based on direct simulation as well as a detailed analysis of the molecular orbitals in μ(3)O. Some of the assignments differ from those given in previous studies. The ZFS effects in the presence of a strong external magnetic field (7 T) prove negligible. The change of the sign of the ZFS changes systematically the intensity of the MCD bands of the z-polarized excitations. The effect of the ZFS on the x,y-polarized excitations is not uniform.

  5. Ab initio and coupled-perturbed density functional theory estimation of zero-field splittings in MnII transition metal complexes.

    Science.gov (United States)

    Zein, Samir; Neese, Frank

    2008-08-28

    The paper presents a method comparison for the prediction of zero-field splitting (ZFS) parameters in a series of Mn (II) coordination complexes. The test set consists of Mn (II) complexes that are experimentally well-characterized by X-ray diffraction and high-field electron paramagnetic resonance. Their ZFS parameters have been calculated using density functional theory (DFT) as well as complete active space self-consistent field (CASSCF) methods. It is shown that the recently introduced coupled-perturbed spin-orbit coupling (CP-SOC) approach [ Neese, F. J. Chem. Phys. 2007, 127, 164112 ] together with hybrid-DFT functionals leads to a slope of the correlation line (plot of experimental vs calculated D values) that is essentially unity provided that the direct spin-spin interaction is properly included in the treatment. This is different from our previous DFT study on the same series of complexes where a severe overestimation of the D parameter has been found [ Zein, S. ; Duboc, C. ; Lubitz, W. ; Neese, F. Inorg. Chem. 2008, 47, 134 ]. CASSCF methods have been used to evaluate the ZFS in an "ab initio ligand-field" type treatment. The study demonstrates that a substantial part of the relevant physics is lost in such a treatment since only excitations within the manganese d-manifold are accounted for. Thus, a severe underestimation of the D parameter has been found. Because the CASSCF calculations in combination with quasidegenerate perturbation theory treats the SOC to all orders, we have nevertheless verified that second-order perturbation theory is an adequate approximation in the case of the high-spin d (5) configuration.

  6. Self-consistent density functional calculations of the crystal field levels in lanthanide and actinide dioxides

    Science.gov (United States)

    Zhou, Fei; Ozoliņš, Vidvuds

    2012-02-01

    Using a recently developed method combining a nonspherical self-interaction corrected LDA + U scheme and an on-site multibody Hamiltonian [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.83.085106 83, 085106 (2011)], we calculate the crystal field parameters and crystal field (CF) excitation levels of f-element dioxides in the fluorite structure with fn electronic configurations, including n=1 (PaO2, PrO2), n=2 (UO2), n=3 (NpO2), and n=4 (PuO2). It is shown that good agreement with experimental data (within approximately 10-20 meV) can be obtained in all cases. The properties of the multielectron CF ground states are analyzed.

  7. Crystal-field investigations of rare-earth-doped wide band gap semiconductors

    CERN Multimedia

    Muller, S; Wahl, U

    Crystal field investigations play a central role in the studies of rare earth doped semiconductors. Optical stark level spectroscopy and lattice location studies of radioactive rare earth isotopes implanted at ISOLDE have provided important insight into these systems during the last years. It has been shown that despite a major site preference of the probe atoms in the lattice, several defect configurations do exist. These sites are visible in the optical spectra but their origin and nature aren't deducible from these spectra alone. Hyperfine measurements on the other hand should reveal these defect configurations and yield the parameters necessary for a description of the optical properties at the atomic scale. In order to study the crystal field with this alternative approach, we propose a new concept for perturbed $\\gamma\\gamma$-angular correlation (PAC) experiments at ISOLDE based on digital signal processing in contrast to earlier analog setups. The general functionality of the spectrometer is explained ...

  8. Phase Transition for a Mixed Spin-1/2 and Spin-sB System with a Transverse Crystal Field

    Institute of Scientific and Technical Information of China (English)

    JIANG Wei; XIAO Gui-Bin; WEI Guo-Zhu; DU An; ZHANG Qi

    2004-01-01

    The critical behaviors of a mixed spin-1/2 and spin-sB Ising system with a transverse crystal field are studied by use of the effective-field theory with correlations. The effect of the transverse crystal field on transition temperatures is investigated numerically for the honeycomb (z = 3) and square (z = 4) lattices. The results show that there is no tricritical point for the system.

  9. Tunable extended depth of field using a liquid crystal annular spatial filter.

    Science.gov (United States)

    Klapp, Iftach; Solodar, Asi; Abdulhalim, Ibrahim

    2014-03-15

    A tunable extended depth of field (EDOF) imaging is presented using temporal multiplexing and a low-cost eight-ring, annular liquid crystal spatial light modulator. By changing between different phase profiles in the pupil plane of a lens we perform several levels of EDOF. Using these levels as a "database" it is shown by temporal multiplexing how to decompose tunable levels of EDOF.

  10. Split supersymmetry in brane models

    Indian Academy of Sciences (India)

    Ignatios Antoniadis

    2006-11-01

    Type-I string theory in the presence of internal magnetic fields provides a concrete realization of split supersymmetry. To lowest order, gauginos are massless while squarks and sleptons are superheavy. For weak magnetic fields, the correct Standard Model spectrum guarantees gauge coupling unification with sin2 W = 3/8 at the com-pactification scale of GUT ≃ 2 × 1016 GeV. I discuss mechanisms for generating gaugino and higgsino masses at the TeV scale, as well as generalizations to models with split extended supersymmetry in the gauge sector.

  11. Split Supersymmetry in String Theory

    CERN Document Server

    Antoniadis, Ignatios

    2006-01-01

    Type I string theory in the presence of internal magnetic fields provides a concrete realization of split supersymmetry. To lowest order, gauginos are massless while squarks and sleptons are superheavy. For weak magnetic fields, the correct Standard Model spectrum guarantees gauge coupling unification with \\sin^2{\\theta_W}=3/8 at the compactification scale of M_{\\rm GUT}\\simeq 2 \\times 10^{16} GeV. I discuss mechanisms for generating gaugino and higgsino masses at the TeV scale, as well as generalizations to models with split extended supersymmetry in the gauge sector.

  12. Evaluation of the exchange interaction and crystal fields in a prototype Dy2 SMM

    Science.gov (United States)

    Zhang, Qing; Sarachik, Myriam; Baker, Michael; Chen, Yizhang; Kent, Andrew; Pineda, Eufemio; McInnes, Eric

    In order to gain an understanding of the INS and magnetization data obtained for Dy2, the simplest member of a newly synthesized family of dysprosium-based molecular magnets, we report on calculations of the magnetic behavior of a Dy2 cluster with the formula [hqH2][Dy2(hq)4(NO3)3].MeOH. The molecular complex contains one high symmetry Dy(III) ion and one low symmetry Dy(III) ion. Our calculations suggest that exchange coupling between the two ions controls the behavior of the magnetization at low temperature, while the crystal field of the low symmetry Dy(III) ion controls the behavior at higher temperature. A point charge electrostatic model, based on crystallographic coordinates, provides a starting point for the determination of the crystal field. Parameters in these calculations are adjusted to provide best fits to inelastic neutron scattering data (INS) and low temperature magnetometry: the INS measurements access crystal field energies and low temperature magnetization probes the Dy-Dy exchange interaction. Work supported by ARO W911NF-13-1-1025 (CCNY) and NSF-DMR-1309202 (NYU).

  13. Beta tricalcium phosphate ceramics with controlled crystal orientation fabricated by application of external magnetic field during the slip casting process.

    Science.gov (United States)

    Hagio, Takeshi; Yamauchi, Kazushige; Kohama, Takenori; Matsuzaki, Toshiya; Iwai, Kazuhiko

    2013-07-01

    Beta tricalcium phosphate (β-TCP) is a resorbable bioceramic that has hitherto been utilized in the medical field. Since it crystallizes in the anisotropic hexagonal system, properties such as chemical and physical ones are expected to depend on its crystal axis direction and/or on its crystal plane (anisotropy). Control of crystal orientation is thus important when used in polycrystalline form. Meanwhile, application of a strong magnetic field has been found to be a promising technique to control crystal orientation of anisotropic shape or structured crystals. In this work, we attempted to fabricate β-TCP ceramics with controlled crystal orientation by applying an external magnetic field during the slip casting process and subsequently sintering them at 1050°C, below the β-α transition temperature. Application of a vertical magnetic field increased intensities of planes perpendicular to c-plane on the top surface, while a horizontal one with simultaneous mechanical mold rotation decreased it. These results indicated that crystal orientation of β-TCP ceramics were successfully controlled by the external magnetic field and together that the magnetic susceptibility of β-TCP is χ(c[perpendicular])>χ(c//).

  14. Novel colloidal system: Magnetite-polymer particles/lyotropic liquid crystal under magnetic field

    Science.gov (United States)

    Mănăilă-Maximean, D.; Cîrtoaje, C.; Dănilă, O.; Donescu, D.

    2017-09-01

    We obtained a new highly ordered colloidal composite using specially manufactured magnetite-polymer nanoparticles and lyotropic liquid crystal. A good compatibility between the components was ensured by the functionalization of the particles during their synthesis. We studied the laser light transmission for the mixtures filled in sandwich-glass cells with homeotropic and planar treatment of the surfaces under external magnetic field. The Fréedericksz transition critical field was estimated, and its' behavior was compared to our new theoretical model based on the Brochard-de Gennes one.

  15. A photonic-crystal optical antenna for extremely large local-field enhancement.

    Science.gov (United States)

    Chang, Hyun-Joo; Kim, Se-Heon; Lee, Yong-Hee; Kartalov, Emil P; Scherer, Axel

    2010-11-08

    We propose a novel design of an all-dielectric optical antenna based on photonic-band-gap confinement. Specifically, we have engineered the photonic-crystal dipole mode to have broad spectral response (Q~70) and well-directed vertical-radiation by introducing a plane mirror below the cavity. Considerably large local electric-field intensity enhancement~4,500 is expected from the proposed design for a normally incident planewave. Furthermore, an analytic model developed based on coupled-mode theory predicts that the electric-field intensity enhancement can easily be over 100,000 by employing reasonably high-Q (~10,000) resonators.

  16. Magnetism of Rare-Earth Compounds with Non-Magnetic Crystal-Field Ground Levels

    Institute of Scientific and Technical Information of China (English)

    LIU Zhao-Sen

    2007-01-01

    @@ Among rare-earth compounds, there are many materials having non-magnetic crystal-field (CF) ground levels.To understand their magnetic behaviour at low temperatures, we study the effects of the CF levels and the Heisenberg-like coupling on the magnetic process of such a crystalline with mean-field and CF theory. It is found that the material can be magnetically ordered if the Heisenberg exchange is sufficiently strong. Additionally we obtain a condition for initial magnetic ordering, and derive a formula for estimating the Curie temperature if the ordering occurs.

  17. Magnetic susceptibility and ground-state zero-field splitting in high-spin mononuclear manganese(III) of inverted N-methylated porphyrin complexes: Mn(2-NCH3NCTPP)Br.

    Science.gov (United States)

    Hung, Sheng-Wei; Yang, Fuh-An; Chen, Jyh-Horung; Wang, Shin-Shin; Tung, Jo-Yu

    2008-08-18

    The crystal structures of diamagnetic dichloro(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N',N'')-tin(IV) methanol solvate [Sn(2-NCH 3NCTPP)Cl 2.2(0.2MeOH); 6.2(0.2MeOH)] and paramagnetic bromo(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N',N'')-manganese(III) [Mn(2-NCH 3NCTPP)Br; 5] were determined. The coordination sphere around Sn (4+) in 6.2(0.2MeOH) is described as six-coordinate octahedron ( OC-6) in which the apical site is occupied by two transoid Cl (-) ligands, whereas for the Mn (3+) ion in 5, it is a five-coordinate square pyramid ( SPY-5) in which the unidentate Br (-) ligand occupies the axial site. The g value of 9.19 (or 10.4) measured from the parallel polarization (or perpendicular polarization) of X-band EPR spectra at 4 K is consistent with a high spin mononuclear manganese(III) ( S = 2) in 5. The magnitude of axial ( D) and rhombic ( E) zero-field splitting (ZFS) for the mononuclear Mn(III) in 5 were determined approximately as -2.4 cm (-1) and -0.0013 cm (-1), respectively, by paramagnetic susceptibility measurements and conventional EPR spectroscopy. Owing to weak C(45)-H(45A)...Br(1) hydrogen bonds, the mononuclear Mn(III) neutral molecules of 5 are arranged in a one-dimensional network. A weak Mn(III)...Mn(III) ferromagnetic interaction ( J = 0.56 cm (-1)) operates via a [Mn(1)-C(2)-C(1)-N(4)-C(45)-H(45A)...Br(1)-Mn(1)] superexchange pathway in complex 5.

  18. Crystal fields of porphyrins and phthalocyanines from polarization-dependent 2p-to-3d multiplets

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Phillip S.; Boukahil, Idris; Himpsel, F. J., E-mail: fhimpsel@wisc.edu [Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States); García-Lastra, J. M. [Department of Energy Conversion and Storage, Technical University of Denmark, 4000 Roskilde (Denmark); Kennedy, Colton K.; Jersett, Nathan J.; Cook, Peter L. [Natural Sciences Department, University of Wisconsin-Superior, Belknap and Catlin, Superior, Wisconsin 54880 (United States)

    2014-03-21

    Polarization-dependent X-ray absorption spectroscopy is combined with density functional calculations and atomic multiplet calculations to determine the crystal field parameters 10Dq, Ds, and Dt of transition metal phthalocyanines and octaethylporphyrins (Mn, Fe, Co, Ni). The polarization dependence facilitates the assignment of the multiplets in terms of in-plane and out-of-plane orbitals and avoids ambiguities. Crystal field values from density functional calculations provide starting values close to the optimum fit of the data. The resulting systematics of the crystal field can be used for optimizing electron-hole separation in dye-sensitized solar cells.

  19. Crystal fields of porphyrins and phthalocyanines from polarization-dependent 2p-to-3d multiplets

    Science.gov (United States)

    Johnson, Phillip S.; García-Lastra, J. M.; Kennedy, Colton K.; Jersett, Nathan J.; Boukahil, Idris; Himpsel, F. J.; Cook, Peter L.

    2014-03-01

    Polarization-dependent X-ray absorption spectroscopy is combined with density functional calculations and atomic multiplet calculations to determine the crystal field parameters 10Dq, Ds, and Dt of transition metal phthalocyanines and octaethylporphyrins (Mn, Fe, Co, Ni). The polarization dependence facilitates the assignment of the multiplets in terms of in-plane and out-of-plane orbitals and avoids ambiguities. Crystal field values from density functional calculations provide starting values close to the optimum fit of the data. The resulting systematics of the crystal field can be used for optimizing electron-hole separation in dye-sensitized solar cells.

  20. Theory of crystal field states for heavy rare-earth impurities in MgB sub 2

    CERN Document Server

    Welsch, F; Faehnle, M

    2002-01-01

    For isolated rare-earth impurities substituting for Mg atoms in the superconductor MgB sub 2 the crystal field parameters are calculated by the ab initio density functional electron theory with constraints for the 4f charge and spin density. The crystal field parameter A sub 6 sup 6 is extremely small due to the structure and bonding properties of MgB sub 2 , and therefore the crystal field levels are nearly exclusively determined by one magnetic quantum number M. Implications for the pair-breaking mechanism of the superconductivity in MgB sub 2 are discussed.

  1. Magnetic field induced strain assisted by stress in Ni-Fe-GaCo single crystals

    Directory of Open Access Journals (Sweden)

    Chumlyakov Y.

    2010-06-01

    Full Text Available Ferromagnetic shape memory alloys (FSMA have the possibility to induced a strain by applying a magnetic field. The main advantage of the FSMA is that the strain cycling frequency is two orders of magnitude higher than coventional shape memory alloys. The best alloy showing this effect is the Ni-Mn-Ga system, with a high mobility of its martensite variants and high magnetocrystalline anisotropy constant. Nevertheless, due to the high brittleness of this alloy, other systems (Ni-Fe-Ga, Co-Ni-Al, Co-Ni-Ga, ... are being investigated as an alternative to Ni-Mn-Ga. In the current work, Ni-Fe-Ga-Co single crystals have been studied. In spite of the formation of L10 martensite (low mobility of the variants, the [001] crystals exhibited magnetic-field-induced strains (in tension larger than 2%, under an assisting tensile stress around 16 MPa and fields below 15 kOe. In martensitic samples previously compressed, application of a constant tensile stress along the same axis together with a perpendicular magnetic field produces the elongation of the sample by variant reorientation, as one of the variants rotates its c axis from the field direction to the stress-axis direction. An estimated magnetostress of ~0.8 MPa is in good agreement with the theoretical value given by the ratio of magnetocrystalline anisotropy constant and twinning shear.

  2. Anisotropic Spin Splitting in Step Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    HAO Ya-Fei; CHEN Yong-Hai; HAO Guo-Dong; WANG Zhan-Guo

    2009-01-01

    By the method of finite difference,the anisotropic spin splitting of the Alx Ga1-x As/GaAs/Aly Ga1-y As/Alx Ga1-x As step quantum wells (QWs) are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field.We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field.The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin.The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.

  3. Urban pattern: Layout design by hierarchical domain splitting

    KAUST Repository

    Yang, Yongliang

    2013-11-01

    We present a framework for generating street networks and parcel layouts. Our goal is the generation of high-quality layouts that can be used for urban planning and virtual environments. We propose a solution based on hierarchical domain splitting using two splitting types: streamline-based splitting, which splits a region along one or multiple streamlines of a cross field, and template-based splitting, which warps pre-designed templates to a region and uses the interior geometry of the template as the splitting lines. We combine these two splitting approaches into a hierarchical framework, providing automatic and interactive tools to explore the design space.

  4. Anisotropies of the lower and upper critical fields in MgB2 single crystals.

    Science.gov (United States)

    Lyard, L; Szabó, P; Klein, T; Marcus, J; Marcenat, C; Kim, K H; Kang, B W; Lee, H S; Lee, S I

    2004-02-01

    The temperature dependence of the upper (H(c2)) and lower (H(c1)) critical fields has been deduced from Hall probe magnetization measurements of high quality MgB2 single crystals along the two main crystallographic directions. We show that Gamma(H(c2))=H(c2 axially ab)/H(c2 axially c) and Gamma(H(c1))=H(c1 axially c)/H(c1 axially ab) differ significantly at low temperature (being approximately 5 and approximately 1, respectively) and have opposite temperature dependencies. We suggest that MgB2 can be described by a single field dependent anisotropy parameter gamma(H) (=lambda(c)/lambda(ab)=xi(ab)/xi(c)) that increases from Gamma(H(c1)) at low field to Gamma(H(c2)) at high field.

  5. Near-field lithography on the azobenzene polymer liquid crystal films

    Institute of Scientific and Technical Information of China (English)

    Douguo Zhang; Jian Liu; Zebo Zhang; Li Cao; Anlian Pan; Pei Wang; Yonghua Lu; Ming Bai; Jun Yang; Lin Tang; Jiangying Zhang; Hai Ming; Qijin Zhang

    2005-01-01

    @@ In this article, we reported near-field research on azobenzene polymer liquid crystal films using scanning near-field optical microscopy (SNOM). Optical writing and subsequently topographic reading of the patterns with subwavelength resolution were carried out in our experiments. Nanometer scale dots and lines were successfully fabricated on the films and the smallest dot diameter is about 120 nm. The width of the line fabricated is about 250 nm. This method is also a choice for nanolithography. The mechanism of the surface deformation on the polymer films was briefly analyzed from the viewpoint of gradient force in the optical near field. The intensity distribution of the electric field near the tip aperture was numerically simulated using finite-difference time-domain (FDTD) method and the numerical simulation results were consistent with the experimental results.

  6. Crystallization Behavior of Anatase Films in Applied Electric Field Heating Process

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this research the TiO2 thin films were prepared by sol-gel dip coating. The crystallization of the films in the applied electric field heating process was thoroughly studied by many technique, differential thermal analysis (DTA), Raman spectroscopy and atomic force microscope (AFM). Furthermore the phase formation, microstructure and photo-catalytic activity of TiO2 film were studied under the condition of an electric field heating-treatment. It is found that the existence of applied electric field promotes the phase transformation from anatase to rutile. Studies on photo-catalytic degradation show that the photo-catalytic activity of TiO2 thin films in an applied electric field is higher.

  7. Spin-orbit contributions in high-spin nitrenes/carbenes: a hybrid CASSCF/MRMP2 study of zero-field splitting tensors.

    Science.gov (United States)

    Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Kitagawa, Masahiro; Takui, Takeji

    2010-10-04

    Zero-field splitting (ZFS) tensors (D tensors) of organic high-spin oligonitrenes/oligocarbenes up to spin-septet are quantitatively determined on the basis of quantum chemical calculations. The spin-orbit contributions, D(SO) tensors are calculated in terms of a hybrid CASSCF/MRMP2 approach, which was recently proposed by us. The spin-spin counterparts, D(SS) tensors are computed based on McWeeny-Mizuno's equation in conjunction with the RODFT spin densities. The present calculations show that more than 10% of ZFS arises from spin-orbit interactions in the high-spin nitrenes under study. Contributions of spin-bearing site-site interactions are estimated with the aid of a semi-empirical model for the D tensors and found to be ca. 5% of the D(SO) tensor. The analysis of intermediate states reveal that the largest contributions to the calculated D(SO) tensors are attributed to intra-site spin flip excitations and delocalized π and π* orbitals play an important role in the inter-site spin-orbit interactions.

  8. A first-principles approach to the calculation of the on-site zero-field splitting in polynuclear transition metal complexes.

    Science.gov (United States)

    Retegan, Marius; Cox, Nicholas; Pantazis, Dimitrios A; Neese, Frank

    2014-11-03

    The interpretation of electron paramagnetic resonance spectra of polynuclear transition metal complexes in terms of individual contributions from each paramagnetic center can be greatly facilitated by the availability of theoretical methods that enable the reliable prediction of local spectroscopic parameters. In this work we report an approach that enables the application of multireference ab initio methods for the calculation of local zero field splitting tensors, one of the leading terms in the spin Hamiltonian for exchange-coupled systems of high nuclearity. The method referred to as local complete active space configuration interaction (L-CASCI) represents a multireference calculation with an active space composed of local orbitals of the center of interest. By successive permutation of the active space to include the localized orbitals corresponding to a particular center of the complex, all on-site parameters can be easily obtained at a high-level of theory with a corresponding low computational cost. Benchmark calculations on synthetic complexes confirm the validity of the approach. As an example of the applicability of the L-CASCI method to large systems, we determine the local anisotropy of the Mn(III) ion of the tetranuclear manganese cluster of photosystem II in both structural forms of its S2 state.

  9. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields.

    Energy Technology Data Exchange (ETDEWEB)

    Armas-Perez, Julio C.; Londono-Hurtado, Alejandro; Guzman, Orlando; Hernandez-Ortiz, Juan P.; de Pablo, Juan J.

    2015-07-27

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

  10. Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

    Energy Technology Data Exchange (ETDEWEB)

    Armas-Pérez, Julio C.; Londono-Hurtado, Alejandro [Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Guzmán, Orlando [Departamento de Física, Universidad Autónoma Metropolitana, Iztapalapa, DF 09340, México (Mexico); Hernández-Ortiz, Juan P. [Departamento de Materiales y Minerales, Universidad Nacional de Colombia, Sede Medellín, Medellín (Colombia); Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Pablo, Juan J. de, E-mail: depablo@uchicago.edu [Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637 (United States); Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2015-07-28

    A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

  11. High magnetic-field scales and critical currents in SmFeAs(O, F) crystals

    Science.gov (United States)

    Moll, Philip J. W.; Puzniak, Roman; Balakirev, Fedor; Rogacki, Krzysztof; Karpinski, Janusz; Zhigadlo, Nikolai D.; Batlogg, Bertram

    2010-08-01

    With the discovery of new superconducting materials, such as the iron pnictides, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates. Although many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed and estimates point to a very high upper critical field, their application potential is less clear. Thus, we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65T. Our detailed study of the transport properties of SmFeAsO0.7F0.25 single crystals reveals a promising combination of high (>2×106Acm-2) and nearly isotropic critical current densities along all crystal directions. This favourable intragrain current transport in SmFeAs(O, F), which shows the highest Tc of 54K at ambient pressure, is a crucial requirement for possible applications. Essential in these experiments are four-probe measurements on focused-ion-beam-cut single crystals with a sub-square-micrometre cross-section, with current along and perpendicular to the crystallographic c axis.

  12. Direct current electric field assembly of colloidal crystals displaying reversible structural color.

    Science.gov (United States)

    Shah, Aayush A; Ganesan, Mahesh; Jocz, Jennifer; Solomon, Michael J

    2014-08-26

    We report the application of low-voltage direct current (dc) electric fields to self-assemble close-packed colloidal crystals in nonaqueous solvents from colloidal spheres that vary in size from as large as 1.2 μm to as small as 0.1 μm. The assemblies are created rapidly (∼2 min) from an initially low volume fraction colloidal particle suspension using a simple capacitor-like electric field device that applies a steady dc electric voltage. Confocal microscopy is used to observe the ordering that is produced by the assembly method. This spatial evidence for ordering is consistent with the 6-fold diffraction patterns identified by light scattering. Red, green, and blue structural color is observed for the ordered assemblies of colloids with diameters of 0.50, 0.40, and 0.29 μm, respectively, consistent with spectroscopic measurements of reflectance. The diffraction and spectrophotometry results were found to be consistent with the theoretical Bragg's scattering expected for closed-packed crystals. By switching the dc electric field from on to off, we demonstrate reversibility of the structural color response on times scales ∼60 s. The dc electric field assembly method therefore represents a simple method to produce reversible structural color in colloidal soft matter.

  13. Imaging the oblique propagation of electrons in germanium crystals at low temperature and low electric field

    Energy Technology Data Exchange (ETDEWEB)

    Moffatt, R. A., E-mail: rmoffatt@stanford.edu; Cabrera, B.; Corcoran, B. M.; Kreikebaum, J. M.; Redl, P.; Shank, B.; Yen, J. J. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Young, B. A. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Department of Physics, Santa Clara University, Santa Clara, California 95053 (United States); Brink, P. L.; Cherry, M.; Tomada, A. [SLAC National Accelerator Facility, Menlo Park, California 94025 (United States); Phipps, A.; Sadoulet, B.; Sundqvist, K. M. [Department of Physics, University of California, Berkeley, California 94720 (United States)

    2016-01-11

    Excited electrons in the conduction band of germanium collect into four energy minima, or valleys, in momentum space. These local minima have highly anisotropic mass tensors which cause the electrons to travel in directions which are oblique to an applied electric field at sub-Kelvin temperatures and low electric fields, in contrast to the more isotropic behavior of the holes. This experiment produces a full two-dimensional image of the oblique electron and hole propagation and the quantum transitions of electrons between valleys for electric fields oriented along the [0,0,1] direction. Charge carriers are excited with a focused laser pulse on one face of a germanium crystal and then drifted through the crystal by a uniform electric field of strength between 0.5 and 6 V/cm. The pattern of charge density arriving on the opposite face is used to reconstruct the trajectories of the carriers. Measurements of the two-dimensional pattern of charge density are compared in detail with Monte Carlo simulations developed for the Cryogenic Dark Matter Search (SuperCDMS) to model the transport of charge carriers in high-purity germanium detectors.

  14. Magnetostrictive behaviors of Fe-Al(001 single-crystal films under rotating magnetic fields

    Directory of Open Access Journals (Sweden)

    Tetsuroh Kawai

    2016-05-01

    Full Text Available Magnetostrictive behaviors of Fe100−x − Alx(x = 0 − 30 at.%(001 single-crystal films under rotating magnetic fields are investigated along the two different crystallographic orientations, [100] and [110]. The behaviors of Fe and Fe90Al10 films show bath-tub like waveform along [100], easy magnetization axis, and triangular waveform along [110], hard magnetization axis, with respect to their four-fold magnetic anisotropy. On the other hand, the behaviors of Fe80Al20 film are different from those of Fe or Fe90Al10 film. The output of the film along [100] shows a strong magnetic field dependence. The Fe70Al30 film shows similar magnetostrictive behaviors along both [100] and [110] reflecting its magnetic properties, which are almost same for the both directions. The growth of ordered phase (B2 in Fe80Al20 and Fe70Al30 films is considered to have affected their magnetostrictive behaviors. The Al content dependence on λ100 and λ111 values shows similar tendency to that reported for the bulk samples but the values are slightly different. The Fe90Al10(001 single-crystal film shows a large magnetostriction along [100] under a very small magnetic field of 0.02 kOe, which is comparable to the saturated one, and changes the value abruptly in relation to the angle of applied magnetic field.

  15. Trapped field properties of a Y–Ba–Cu–O bulk by pulsed field magnetization using a split coil inserted by iron yokes with various geometries and electromagnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, K., E-mail: t2216017@iwate-u.ac.jp [Department of Physical Science and Materials Engineering, Faculty of Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551 (Japan); Ainslie, M.D. [Bulk Superconductivity Group, Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ (United Kingdom); Fujishiro, H.; Naito, T. [Department of Physical Science and Materials Engineering, Faculty of Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551 (Japan); Shi, Y-H.; Cardwell, D.A. [Bulk Superconductivity Group, Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ (United Kingdom)

    2017-05-15

    Highlights: • The trapped field characteristics of a standard Y–Ba–Cu–O bulk magnetized by PFM was investigated using a split coil with three kinds of iron yokes inserted in the bores of coil,both experimentally and numerically. • Numerical results encourage better understanding of the role of yoke, including the typical behavior of the magnetic flux, such as a flux jump during PFM. • A higher saturation magnetic flux density of the yoke material was effective to reduce flux flow in the descending stage of the pulsed field. • A conductivity of the yoke material also acts to reduce the velocity of the flux intruding the bulk because of eddy currents that flow in the yoke that oppose the magnetization, which reduces the temperature rise in the bulk. - Abstract: We have investigated, both experimentally and numerically, the trapped field characteristics of a standard Y–Ba–Cu–O bulk of 30 mm in diameter and 14 mm in thickness magnetized by pulsed field magnetization (PFM) using a split coil, in which three kinds of iron yoke are inserted in the bore of the coil: soft iron with a flat surface, soft iron with a taper, and permendur (50Fe + 50Co alloy) with a flat surface. The highest trapped field, B{sub Tmax}, of 2.93 T was achieved at 40 K in the case of the permendur yoke, which was slightly higher than that obtained for the flat soft iron or the tapered soft iron yokes, and was much higher than 2.20 T in the case without the yoke. The insertion effect of the yoke on the trapped field characteristics was also investigated using numerical simulations. The results suggest that the saturation magnetic flux density, B{sub sat}, of the yoke acts to reduce the flux flow due to its hysteretic magnetization curve and the higher electrical conductivity, σ, of the yoke material also acts to suppress the flux increase rate. A flux jump (or flux leap) can be reproduced in the ascending stage of PFM using numerical simulation, using an assumption of relatively

  16. Orientation of growing crystals of Co- or Gd-containing L-threonine dehydrogenase by magnetic fields

    Science.gov (United States)

    Maki, Syou; Ishikawa, Kazuhiko; Ataka, Mitsuo

    2009-12-01

    L-Threonine dehydrogenase from Pyrococcus horikoshii (TDH) is a water-soluble metalloenzyme, the molecular structure of which has been unknown until recently. The Zn 2+ ion in the native TDH, prepared as a recombinant protein, is replaced artificially with Co 2+, Ni 2+ or Gd 3+. These samples are crystallized in homogeneous magnetic fields of 2-10 T. Half of the Co- or Gd-substituted crystals show magnetic orientation in a field of 2 T at 278 K whereas the crystals of the native TDH require a 4 T magnetic field for half orientation. The sensitivity to magnetic orientation can thus be increased by metal substitution. On the other hand, we cannot assign clear changes in the size, number, and quality of the native and metal-substituted crystals with and without the presence of the magnetic field.

  17. Anisotropy and Magnetostriction in Cobalt-Modified Magnetite: A Crystal Field Approach

    Science.gov (United States)

    Nlebedim, Cajetan; Jiles, David

    2013-03-01

    The anisotropy and magnetostrictive properties of magnetite are altered by the introduction of cobalt ions into the spinel crystal lattice. 4% of Co2+ substituted for Fe2+ changes both the sign and magnitude of magnetocrystalline anisotropy coefficient. Such strong dependence can be useful for tailoring the properties of cobalt-iron oxides for applications. This is especially important, considering that cobalt ferrite materials prepared for magnetostrictive, multiferroic and other related applications often deviate from targeted or stoichiometric compositions. In this study, magnetite has been systematically modified by substitution of cobalt. The changes in anisotropy and magnetostriction have been studied and can be explained using the single ion model. The agreement between the trend observed in this experimental investigation and previous theoretical studies is noteworthy. The variation in anisotropy and magnetostriction will be presented on the basis of two competing factors; the unquenched orbital angular momentum of Co2+ and changes in the crystal field due to Co2+ substitution.

  18. Deflecting Easy-axis of Fe304 Single Crystal Nanowires by Magnetic-field-induced Method

    Institute of Scientific and Technical Information of China (English)

    W. Wang; S. Y. Wang

    2012-01-01

    In order to control the orientation of easy-axis of magnetic nanowires, FesO4 single crystal nanowires with easy-axis perpendicular to wire-axis were prepared successfully by means of a magnetic-field-induced method. Analysis of X-ray diffraction and electron diffraction pattern showed that there was a wide-angle deflection of easy-axis in the prepared Fe304 nanowires. A high saturation magnetization (82 emu/g) of the FesO4 nanowires was achieved at room temperature. The benefits and mechanism of the deflection of easy-axis from its wire-axis in FesO4 single crystal nanowires were discussed. The results are expected to broaden the magnetic properties of traditional ferrite nanowires.

  19. Development of specialized modelling tools for crystal growth processes with magnetic fields

    Science.gov (United States)

    Rudevics, A.; Muiznieks, A.; Nacke, B.

    2007-06-01

    The present paper is devoted to some aspects of the development of specialized software for the modelling of crystal growth processes with magnetic fields. Due to the complexity of the mathematical models for such processes, the modern technology of software design and implementation has to be used. Our experience in numerical modelling of crystal growth processes has shown that such approach facilitates the development of complex software systems. It involves the so-called object-oriented design and programming as well as the use of powerful software libraries in order to benefit from its functionality. To illustrate the programs created by our group, some examples are briefly described in this paper. Figs 7, Refs 13.

  20. On the binding of small polarons in a mean-field quantum crystal

    CERN Document Server

    Lewin, Mathieu

    2012-01-01

    We consider a small multi-polaron model obtained by coupling the many-body Schr\\"odinger equation for N interacting electrons with the energy functional of a mean- field crystal with a localized defect, obtaining a highly non linear many-body problem. The physical picture is that the electrons constitue a charge defect in an otherwise perfect periodic crystal. A remarkable feature of such a system is the possibility to form a bound state of electrons via their interaction with the polarizable background. We first prove that a single polaron always binds, i.e. the energy functional has a minimizer for N = 1. Then we discuss the case of multi-polarons containing two electrons or more. We show that their existence is guaranteed when certain quantized binding inequalities of HVZ type are satisfied.

  1. Crystal field-phonon coupling in the Kondo lattice CeCu2

    Science.gov (United States)

    Witte, U.; Kramp, S.; Braden, M.; Svoboda, P.; Loewenhaupt, M.

    CeCu2 is a Kondo lattice and shows antiferromagnetic order below 3.5K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons.

  2. Crystal field-phonon coupling in the Kondo lattice CeCu{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Witte, U. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany); HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Kramp, S. [HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Braden, M. [LLB Saclay, 91191 Gif-Sur-Yvette Cedex (France); Svoboda, P. [Charles University, 12116 Praha (Czech Republic); Loewenhaupt, M. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany)

    2002-07-01

    CeCu{sub 2} is a Kondo lattice and shows antiferromagnetic order below 3.5 K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150 K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons. (orig.)

  3. Zero-field splitting in pseudotetrahedral Co(II) complexes: a magnetic, high-frequency and -field EPR, and computational study.

    Science.gov (United States)

    Idešicová, Monika; Titiš, Ján; Krzystek, J; Boča, Roman

    2013-08-19

    Six pseudotetrahedral cobalt(II) complexes of the type [CoL2Cl2], with L = heterocyclic N-donor ligand, have been studied in parallel by magnetometry, and high-frequency and -field electron paramagnetic resonance (HFEPR). HFEPR powder spectra were recorded in a 50 GHz < ν < 700 GHz range in a 17 T superconducting and 25 T resistive magnet, which allowed constructing of resonance field vs frequency diagrams from which the fitting procedure yielded the S = 3/2 spin ground state Hamiltonian parameters. The sign of the axial anisotropy parameter D was determined unambiguously; the values range between -8 and +11 cm(-1) for the given series of complexes. These data agree well with magnetometric analysis. Finally, quantum chemical ab initio calculations were performed on the whole series of complexes to probe the relationship between the magnetic anisotropy, electronic, and geometric structure.

  4. Crystal fields of porphyrins and phthalocyanines from polarization-dependent 2p-to-3d multiplets

    OpenAIRE

    Johnson, Phillip S.; García Lastra, Juan Maria; Kennedy, Colton K.; Jersett, Nathan J.; Boukahil, Idris; Himpsel, F. J.; Cook, Peter L.

    2014-01-01

    Polarization-dependent X-ray absorption spectroscopy is combined with density functional calculations and atomic multiplet calculations to determine the crystal field parameters 10Dq, Ds, and Dt of transition metal phthalocyanines and octaethylporphyrins (Mn, Fe, Co, Ni). The polarization dependence facilitates the assignment of the multiplets in terms of in-plane and out-of-plane orbitals and avoids ambiguities. Crystal field values from density functional calculations provide starting value...

  5. Melt Motion Due to Peltier Marking During Bridgman Crystal Growth with an Axial Magnetic Field

    Science.gov (United States)

    Sellers, C. C.; Walker, John S.; Szofran, Frank R.; Motakef, Shariar

    2000-01-01

    This paper treats a liquid-metal flow inside an electrically insulating cylinder with electrically conducting solids above and below the liquid region. There is a uniform axial magnetic field, and there is an electric current through the liquid and both solids. Since the lower liquid-solid interface is concave into the solid and since the liquid is a better electrical conductor than the adjacent solid, the electric current is locally concentrated near the centerline. The return to a uniform current distribution involves a radial electric current which interacts with the axial magnetic field to drive an azimuthal flow. The axial variation of the centrifugal force due to the azimuthal velocity drives a meridional circulation with radial and axial velocities. This problem models the effects of Peltier marking during the vertical Bridgman growth of semiconductor crystals with an externally applied magnetic field, where the meridional circulation due to the Peltier Current may produce important mixing in the molten semiconductor.

  6. Enhanced electrocaloric cooling in ferroelectric single crystals by electric field reversal

    Science.gov (United States)

    Ma, Yang-Bin; Novak, Nikola; Koruza, Jurij; Yang, Tongqing; Albe, Karsten; Xu, Bai-Xiang

    2016-09-01

    An improved thermodynamic cycle is validated in ferroelectric single crystals, where the cooling effect of an electrocaloric refrigerant is enhanced by applying a reversed electric field. In contrast to the conventional adiabatic heating or cooling by on-off cycles of the external electric field, applying a reversed field is significantly improving the cooling efficiency, since the variation in configurational entropy is increased. By comparing results from computer simulations using Monte Carlo algorithms and experiments using direct electrocaloric measurements, we show that the electrocaloric cooling efficiency can be enhanced by more than 20% in standard ferroelectrics and also relaxor ferroelectrics, like Pb (Mg1 /3 /Nb2 /3)0.71Ti0.29O3 .

  7. Bifurcation properties of nematic liquid crystals exposed to an electric field: Switchability, bistability, and multistability

    KAUST Repository

    Cummings, L. J.

    2013-07-01

    Bistable liquid crystal displays (LCDs) offer the potential for considerable power savings compared with conventional (monostable) LCDs. The existence of two (or more) stable field-free states that are optically distinct means that contrast can be maintained in a display without an externally applied electric field. An applied field is required only to switch the device from one state to the other, as needed. In this paper we examine the basic physical principles involved in generating multiple stable states and the switching between these states. We consider a two-dimensional geometry in which variable surface anchoring conditions are used to control the steady-state solutions and explore how different anchoring conditions can influence the number and type of solutions and whether or not switching is possible between the states. We find a wide range of possible behaviors, including bistability, tristability, and tetrastability, and investigate how the solution landscape changes as the boundary conditions are tuned. © 2013 American Physical Society.

  8. Field analysis of TE and TM modes in photonic crystal Bragg fibers by transmission matrix method

    Directory of Open Access Journals (Sweden)

    M Hosseini Farzad

    2010-03-01

    Full Text Available In this article, we considered the field analysis in photonic crystal Bragg fibers. We apply the method of transmission matrix to calculater the dispersion curves, the longitudinal wave number over wave number versus incident wavelength, and the field distributions of TE and TM modes in the Bragg fiber. Our analysis shows that the field of guided modes is confined in the core and can exist only in particular wavelength bands corresponding to the band-gap of the periodic structure of the clad. From another point of view, light confinement is due to Bragg reflection from high-and low-refractive index layers of the clad. Also, the diagram of average angular frequency with respect to average longitudinal wave number is plotted so that the band gap regions of the clad are clearly observed.

  9. Near-field characterization of low-loss photonic crystal waveguides

    DEFF Research Database (Denmark)

    Volkov, V. S.; Bozhevolnyi, S. I.; Borel, Peter Ingo

    2005-01-01

    A scanning near-field optical microscope is used to directly map the propagation of light in the wavelength range of 1500-1630 nm along straight photonic crystal waveguides (PCWs) fabricated on silicon-on-insulator wafers. The PVWs were formed by removing a single row of holes in the triangular 428......-nm-period lattices with different filling factors (0.76 and 0.82) and connected to access ridge waveguides. Using the near-field optical images we investigate the light propagation along PCWs for TM and TE polarization (the electric field is perpendicular/parallel to the sample surface). Efficient...... guiding (for both samples) of the TM-polarized radiation is observed in the whole range of laser tunability. For TE polarization, the efficient guiding is limited to the wavelengths shorter than 1552 or 1570 nm for the PCW with the filling factor of 0.76 or 0.82, respectively. For longer wavelengths, we...

  10. 3D global analysis of CZ-Si growth in a transverse magnetic field with rotating crucible and crystal

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Lijun; Kakimoto, Koichi [Research Institute for Applied Mechanics, Kyushu University, 6-1, Kasuga-Koen, Kasuga 816-8580 (Japan)

    2005-04-01

    Three-dimensional global simulations were carried out for a small Czochralski furnace for silicon crystal growth with a recently developed global model. The furnace is placed in a transverse magnetic field with rotating crucible and crystal. The convective, conductive and radiative heat transfers in the entire furnace were solved in a three-dimensionally conjugated way. Three-dimensional distributions of temperature and velocity were analyzed. The melt-crystal interface was found to have nearly rotational symmetry, and the azimuthal non-uniformity of temperature is much weaker on the crystal and crucible sidewalls in the case of high rotation rates of crucible and crystal than in the case of non-rotating crucible and crystal. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Standard Model Particles from Split Octonions

    Directory of Open Access Journals (Sweden)

    Gogberashvili M.

    2016-01-01

    Full Text Available We model physical signals using elements of the algebra of split octonions over the field of real numbers. Elementary particles are corresponded to the special elements of the algebra that nullify octonionic norms (zero divisors. It is shown that the standard model particle spectrum naturally follows from the classification of the independent primitive zero divisors of split octonions.

  12. Standard Model Particles from Split Octonions

    CERN Document Server

    Gogberashvili, Merab

    2016-01-01

    We model physical signals using elements of the algebra of split octonions over the field of real numbers. Elementary particles are corresponded to the special elements of the algebra that nullify octonionic norms (zero divisors). It is shown that the standard model particle spectrum naturally follows from the classification of the independent primitive zero divisors of split octonions.

  13. 2-Photon tandem device for water splitting

    DEFF Research Database (Denmark)

    Seger, Brian; Castelli, Ivano Eligio; Vesborg, Peter Christian Kjærgaard;

    2014-01-01

    Within the field Of photocatalytic water splitting there are several strategies to achieve the goal of efficient and cheap photocatalytic water splitting. This work examines one particular strategy by focusing on monolithically stacked, two-photon photoelectrochemical cells. The overall aim of th...

  14. Optical electric-field sensor based on angular optical bias using single β-BaB2O4 crystal.

    Science.gov (United States)

    Li, Changsheng; Shen, Xiaoli; Zeng, Rong

    2013-11-01

    A novel optical electric-field sensor is proposed and demonstrated in experiment by use of a single beta barium borate (β-BaB2O4, BBO) crystal. The optical sensing unit is only composed of one BBO crystal and two polarizers. An optical phase bias of 0.5π is provided by using natural birefringence in the BBO crystal itself. A small angle (e.g., 0.6°) between the sensing light beam and principal axis of the crystal is required in order to produce the above optical bias. Thus the BBO crystal is used as the electric-field-sensing element and quarter waveplate. The ac electric field in the range of (1.4-703.2) kV/m has been measured with measurement sensitivity of 1.39 mV/(kV/m) and nonlinear error of 0.6%. Compared with lithium niobate crystal used as an electric-field sensor, main advantages of the BBO crystal include higher measurement sensitivity, compact configuration, and no ferroelectric ringing effect.

  15. Large field-induced-strain at high temperature in ternary ferroelectric crystals

    Science.gov (United States)

    Wang, Yaojin; Chen, Lijun; Yuan, Guoliang; Luo, Haosu; Li, Jiefang; Viehland, D.

    2016-10-01

    The new generation of ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ferroelectric single crystals have potential applications in high power devices due to their surperior operational stability relative to the binary system. In this work, a reversible, large electric field induced strain of over 0.9% at room temperature, and in particular over 0.6% above 380 K was obtained. The polarization rotation path and the phase transition sequence of different compositions in these ternary systems have been determined with increasing electric field applied along [001] direction based on x-ray diffraction data. Thereafter, composition dependence of field-temperature phase diagrams were constructed, which provide compositional and thermal prospectus for the electromechanical properties. It was found the structural origin of the large stain, especially at higher temperature is the lattice parameters modulated by dual independent variables in composition of these ternary solid solution crystals.

  16. Calculation of crystal-field parameters for rare-earth noble metal alloys

    Energy Technology Data Exchange (ETDEWEB)

    Steinbeck, L. [MPG Research Group `Electron Systems`, Department of Physics, University of Technology, Mommsenstr. 13, D-01062, Dresden (Germany); Richter, M. [MPG Research Group `Electron Systems`, Department of Physics, University of Technology, Mommsenstr. 13, D-01062, Dresden (Germany); Eschrig, H. [MPG Research Group `Electron Systems`, Department of Physics, University of Technology, Mommsenstr. 13, D-01062, Dresden (Germany); Nitzsche, U. [MPG Research Group `Electron Systems`, Department of Physics, University of Technology, Mommsenstr. 13, D-01062, Dresden (Germany)

    1995-02-09

    The crystal-field (CF) parameters for 4f electrons of a series of rare-earth impurities in Ag and Au have been evaluated from first-principles density functional calculations of the charge distribution which are based on an optimized LCAO scheme. The localized 4f states are treated as `open core shell`. By including the self-interaction correction for the 4f states, artificial constraints on the 4f charge density employed in earlier density functional CF calculations are avoided. The calculated parameters are compared with recent neutron scattering data. ((orig.)).

  17. Calculation of crystal-field parameters for rare-earth noble metal alloys

    Science.gov (United States)

    Steinbeck, L.; Richter, M.; Eschrig, H.; Nitzsche, U.

    1995-02-01

    The crystal-field (CF) parameters for 4f electrons of a series of rare earth impurities in Ag and Au have been evaluated from first-principles density functional calculations of the charge distribution which are based on an optimized LCAO scheme. The localized 4f states are treated as 'open core shell'. By including the self-interaction correction for the 4f states, artificial constraints on the 4f charge density employed in earlier density functional CF calculations are avoided. The calculated parameters are compared with recent neutron scattering data.

  18. Linearly first- and second-order, unconditionally energy stable schemes for the phase field crystal model

    Science.gov (United States)

    Yang, Xiaofeng; Han, Daozhi

    2017-02-01

    In this paper, we develop a series of linear, unconditionally energy stable numerical schemes for solving the classical phase field crystal model. The temporal discretizations are based on the first order Euler method, the second order backward differentiation formulas (BDF2) and the second order Crank-Nicolson method, respectively. The schemes lead to linear elliptic equations to be solved at each time step, and the induced linear systems are symmetric positive definite. We prove that all three schemes are unconditionally energy stable rigorously. Various classical numerical experiments in 2D and 3D are performed to validate the accuracy and efficiency of the proposed schemes.

  19. Light quasiparticles dominate electronic transport in molecular crystal field-effect transistors

    Energy Technology Data Exchange (ETDEWEB)

    Li, Z. Q.; Podzorov, V.; Sai, N.; Martin, Michael C.; Gershenson, M. E.; Di Ventra, M.; Basov, D. N.

    2007-03-01

    We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m[small star, filled]comparable to free electron mass. Furthermore, the m[small star, filled]values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.

  20. Electrical Impact of SiC Structural Crystal Defects on High Electric Field Devices (Invited)

    Science.gov (United States)

    Neudeck, Philip G.

    1999-01-01

    As illustrated by the invited paper at this conference and other works, SiC wafers and epilayers contain a variety of crystallographic imperfections, including micropipes, closed-core screw dislocations, grain boundaries, basal plane dislocations, heteropolytypic inclusions, and surfaces that are often damaged and contain atomically rough features like step bunching and growth pits or hillocks. Present understanding of the operational impact of various crystal imperfections on SiC electrical devices is reviewed, with an emphasis placed on high-field SiC power devices and circuits.

  1. Ambipolar Cu- and Fe-Phthalocyanine single-crystal field-effect transistors

    OpenAIRE

    de Boer, R. W. I.; Stassen, A. F.; Craciun, M. F.; Mulder, C. L.; Molinari, A; Rogge, S.; Morpurgo, A. F.

    2005-01-01

    We report the observation of ambipolar transport in field-effect transistors fabricated on single crystals of Copper- and Iron-Phthalocyanine, using gold as a high work-function metal for the fabrication of source and drain electrodes. In these devices, the room-temperature mobility of holes reaches 0.3 cm$^2$/Vs in both materials. The highest mobility for electrons is observed for Iron-Phthalocyanines and is approximately one order of magnitude lower. Our measurements indicate that these val...

  2. Electric field induced domain formation in surface stabilized ferroelectric liquid crystal cells

    OpenAIRE

    Dierking, Ingo; Gießelmann, Frank; Schacht, Jochen; Zugenmaier, Peter

    1994-01-01

    Two types of domains have been observed for S sub(C) ferroelectric liquid crystals in surface stabilized cells (SSFLC) by application of a high electric field with the smectic layers tilted by the amount of the chevron angle with respect to the normal of the rubbing direction in the substrate plane. The layer structure resembles that of a chevron configuration in the plane of the substrate similar to the recently reported stripe-shaped SSFLC structure. The two domain types 'appear' to switch ...

  3. Field induced microwave absorption in single crystal Bi (2212): Evidence for a superconductive glass state

    Energy Technology Data Exchange (ETDEWEB)

    Tyagi, S.; Gould, A.; Bhagat, S.M. (Centre for Research on Superconductivity, Dept. of Physics, Univ. of Maryland, College Park (USA)); Manheimer, M.A. (Lab. for Physical Sciences, College Park, MD (USA))

    1989-12-01

    The field induced microwave absorption P(H) at 35 GHz in Bi 2212 micaceous single crystals exhibits remarkable variations as temperature is increased from 1.3 K to Tc. For T< or approx.16 K, the hysteresis loops are highly reminiscent of those observed in spin glasses. At 30< or approx.T< or approx.50 K, they resemble those of a Type II superconductor. As suggested by the magnetization data, the micaceous nature causes a large enhancement in P(H) for 50

  4. Tunable far-field acoustic imaging by two-dimensional sonic crystal with concave incident surface

    Science.gov (United States)

    Shen, Feng-Fu; Lu, Dan-Feng; Zhu, Hong-Wei; Ji, Chang-Ying; Shi, Qing-Fan

    2017-01-01

    An additional concave incident surface comprised of two-dimensional (2D) sonic crystals (SCs) is employed to tune the acoustic image in the far-field region. The tunability is realized through changing the curvature of the concave surface. To explain the tuning mechanism, a simple ray-trace analysis is demonstrated based on the wave-beam negative refractive law. Then, a numerical confirmation is carried out. Results show that both the position and the intensity of the image can be tuned by the introduced concave surface.

  5. Quasi-Restricted Orbital Treatment for the Density Functional Theory Calculations of the Spin-Orbit Term of Zero-Field Splitting Tensors.

    Science.gov (United States)

    Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji

    2016-12-15

    A quasi-restricted orbital (QRO) approach for the calculation of the spin-orbit term of zero-field splitting tensors (D(SO) tensors) by means of density functional theory (DFT) importantly features in the fact that it is free from spin contamination problems because it uses spin eigenfunctions for the zeroth order wave functions. In 2011, however, Schmitt and co-workers pointed out that in the originally proposed QRO working equation some possible excitations were not included in their sum-over-states procedure, which causes spurious D(SO) contributions from closed-shell subsystems located far from the magnetic molecule under study. We have revisited the derivation of the QRO working equation and modified it, making it include all possible types of excitations in the sum-over-states procedure. We have found that the spurious D(SO) contribution can be eliminated by taking into account contributions from all possible types of singly excited configuration state functions. We have also found that only the SOMO(α) → SOMO(β) excited configurations have nonzero contributions to the D(SO) tensors as long as α and β spin orbitals have the same spatial distributions and orbital energies. For the D(SO) tensor calculations, by using a ground state wave function free from spin contamination, we propose a natural orbital-based Pederson-Khanna (NOB-PK) method, which utilizes the single determinant wave function consisting of natural orbitals in conjunction with the Pederson-Khanna (PK) type perturbation treatment. Some relevant calculations revealed that the NOB-PK method can afford more accurate D(SO) tensors than the conventional PK method as well as the QRO approach in Mn(II) complexes and Re(IV)-based single molecule magnets.

  6. W-band EPR studies of high-spin nitrenes with large spin-orbit contribution to zero-field splitting

    Science.gov (United States)

    Akimov, Alexander; Masitov, Artem; Korchagin, Denis; Chapyshev, Sergei; Misochko, Eugenii; Savitsky, Anton

    2015-08-01

    First W-band 94 GHz EPR spectra of randomly oriented triplet, quintet, and septet nitrenes formed during the photolysis of 1,3,5-triazido-2,4,6-tribromobenzene in cryogenic matrices are reported. In comparison with conventional X-band 9 GHz electron paramagnetic resonance (EPR) spectroscopy, W-band EPR spectroscopy allows the detection and complete spectroscopic characterization of all paramagnetic species formed at different stages of the photolysis of aromatic polyazides. This type of spectroscopy is of paramount importance for experimental determination of the sign of the zero-field splitting (ZFS) parameters of high-spin molecules with large spin-orbit contribution to the ZFS, caused by the effect of heavy atoms. The study shows that triplet 1,3-diazido-2,4,6-tribromo-5-nitrenobenzene (T1) has DT = 1.369 cm-1, ET = 0.093 cm-1, and g = 2.0033, quintet 1-azido-2,4,6-tribromo-3,5-dinitrenobenzene (Q1) shows DQ = - 0.306 cm-1, EQ = 0.0137 cm-1, and g = 2.0070, and septet 2,4,6-tribromo-1,3,5-trinitrenobenzene (S1) has DS = - 0.203 cm-1, ES = 0, and g = 2.0073. The experimental ZFS parameters agree well with the results of density functional theory calculations at the PBE/Ahlrichs-DZ level of theory, showing that such calculations adequately describe the magnetic properties of bromine-containing high-spin nitrenes. Both experimental and theoretical data indicate that, in contrast to all known to date quintet dinitrenes, dinitrene Q1 has the negative sign of magnetic anisotropy due to the "heavy atom effect." This dinitrene along with septet trinitrene S1 possess the largest negative value of D among all known quintet and septet organic polyradicals.

  7. Rigorous analysis of an electric-field-driven liquid crystal lens for 3D displays

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Bong-Sik; Lee, Seung-Chul; Park, Woo-Sang [Inha University, Incheon (Korea, Republic of)

    2014-08-15

    We numerically analyzed the optical performance of an electric field driven liquid crystal (ELC) lens adopted for 3-dimensional liquid crystal displays (3D-LCDs) through rigorous ray tracing. For the calculation, we first obtain the director distribution profile of the liquid crystals by using the Erickson-Leslie motional equation; then, we calculate the transmission of light through the ELC lens by using the extended Jones matrix method. The simulation was carried out for a 9 view 3D-LCD with a diagonal of 17.1 inches, where the ELC lens was slanted to achieve natural stereoscopic images. The results show that each view exists separately according to the viewing position at an optimum viewing distance of 80 cm. In addition, our simulation results provide a quantitative explanation for the ghost or blurred images between views observed from a 3D-LCD with an ELC lens. The numerical simulations are also shown to be in good agreement with the experimental results. The present simulation method is expected to provide optimum design conditions for obtaining natural 3D images by rigorously analyzing the optical functionalities of an ELC lens.

  8. Numerical analysis of near and far field patterns of second-harmonic generation with tiling nonlinear optical crystals

    Energy Technology Data Exchange (ETDEWEB)

    Harimoto, T [Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11 Kofu, Yamanashi 400-8511 (Japan); Shiraga, H [Institute of Laser Engineering, Osaka University, Suita, Osaka (Japan)], E-mail: harimoto@yamanashi.ac.jp

    2008-05-01

    We report numerical analysis of near- and far-field patterns of the second-harmonic wave in a large-scale high-power laser used in the laser fusion with type I KDP crystals arranged in a tiling style. The thickness and phase-matching angle of the tiling crystals are designed based on the near-field pattern of the second-harmonic wave. The tilting angle error and thickness difference of the tiling crystals are evaluated by the energy distribution included in the Airy spot of the far-field pattern at the focal point. The parallelism and flatness of the tiling crystals can also be estimated with the same method.

  9. Ionization of Atoms and the Thomas-Fermi Model for the Electric Field in Crystal Planar Channels

    Institute of Scientific and Technical Information of China (English)

    LIUYing-Tai; ZHANGQi-Ren; 等

    2002-01-01

    The electric field in the crystal planar channels is studied by the Thomas-Fermi method.The ThomasFermi equation and the corresponding boundary conditions are derived for the crystal palanar channels,The numerical solution for the elctric field in the channels between(110) Planes of the single crystal silicaon and the critical angles of channelling protons in them are shown.Reasonable agreements with the experimental data are obtained.The results show that the Thomas-Fermi method for the crystal works well in this study,and a microscopic research of the channel electric field with the contribution of all atoms and the atomic ionization being taken into account is practical.

  10. Crystal field analysis of Nd{sup 3+} energy levels in monoclinic NdAl{sub 3}(BO{sub 3}){sub 4} laser

    Energy Technology Data Exchange (ETDEWEB)

    Cascales, C.; Zaldo, C. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Cantoblanco, Madrid (Spain); Caldino, U. [Departamento de Fisica, Universidad Autonoma Metropolitana, Iztapalapa, Mexico DF (Mexico); Garcia Sole, J. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Cantoblanco, Madrid (Spain); Luo, Z.D. [Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian (China)

    2001-09-03

    The energies of 135 Kramers doublets extending up to the {sup 2}H1{sub 11/2} multiplet for Nd{sup 3+} in a monoclinic C2/c space group (No 15) NdAl{sub 3}(BO{sub 3}){sub 4} (NAB) single crystal laser have been determined from polarized optical absorption and photoluminescence measurements at 7 K. The strongly polarized character of the Nd spectra has been discussed under the assumption of a local D{sub 3} symmetry, higher than the C{sub 2} symmetry of NAB, and the observed energy levels have been labelled with the adequate crystal quantum numbers and irreducible representations. A detailed Hamiltonian of 21 parameters has been used in the simulation of the energy levels and associated wavefunctions of the 4f{sup 3} configuration of Nd{sup 3+}. The diagonalized complete energy matrix combines simultaneously the free-ion and single-particle crystal field interactions. Starting B{sup k}{sub q} CF parameters were calculated from the semi-empirical simple overlap model SOM. A comparative simulation considering the C{sub 2} symmetry of NAB is provided. Moreover, two-electron CF interactions as well as an empirical correction have been tested in calculating the anomalous splitting of the {sup 2}H2{sub 11/2} levels. A final fit in D{sub 3} symmetry produces a very good adjustment with a low rms deviation {sigma}=15.3 cm{sup -1} between observed and calculated energy levels. (author)

  11. How Do Heavier Halide Ligands Affect the Signs and Magnitudes of the Zero-Field Splittings in Halogenonickel(II) Scorpionate Complexes? A Theoretical Investigation Coupled to Ligand-Field Analysis.

    Science.gov (United States)

    Ye, Shengfa; Neese, Frank

    2012-07-10

    This work presents a detailed analysis of the physical origin of the zero-field splittings (ZFSs) in a series of high-spin (S = 1) nickel(II) scorpionate complexes Tp*NiX (Tp* = hydrotris(3,5-dimethylpyrazole)borate, X = Cl, Br, I) using quantum chemical approaches. High-frequency and -field electron paramagnetic resonance studies have shown that the complexes with heavier halide ligands (Br, I) have greater magnitudes but opposite signs of the ZFSs compared with the chloro congener (Desrochers, P. J.; Telser, J.; Zvyagin, S. A.; Ozarowski, A.; Krzystek, J.; Vicic, D. A. Inorg. Chem.2006, 45, 8930-8941). To rationalize the experimental findings, quantum chemical calculations of the ZFSs in this Ni(II) halide series have been conducted. The computed ZFS using wave-function-based ab initio methods (state-averaged CASSCF, NEVPT2, and SORCI) are in good agreement with the experiment. For comparison, density functional theory was only marginally successful. The ligand-field analysis demonstrates that the signs and magnitudes of the ZFSs are subtly determined by the trade-off between the negative contributions from the (1,3)A1(1e→2e) transitions relative to the positive contributions from the remaining d-d excited states. The term from (1,3)A1(1e→2e) stems from the structural feature that the metal center displaces out of the equatorial plane, and gains the importance when heavier halide ligand is involved.

  12. A Phase Field Technique for Modeling and Predicting Flow Induced Crystallization Morphology of Semi-Crystalline Polymers

    Directory of Open Access Journals (Sweden)

    Xiaodong Wang

    2016-06-01

    Full Text Available Flow induced crystallization of semi-crystalline polymers is an important issue in polymer science and engineering because the changes in morphology strongly affect the properties of polymer materials. In this study, a phase field technique considering polymer characteristics was established for modeling and predicting the resulting morphologies. The considered crystallization process can be divided into two stages, which are nucleation upon the flow induced structures and subsequent crystal growth after the cessation of flow. Accordingly, the proposed technique consists of two parts which are a flow induced nucleation model based on the calculated information of molecular orientation and stretch, and a phase field crystal growth model upon the oriented nuclei. Two-dimensional simulations are carried out to predict the crystallization morphology of isotactic polystyrene under an injection molding process. The results of these simulations demonstrate that flow affects crystallization morphology mainly by producing oriented nuclei. Specifically, the typical skin-core structures along the thickness direction can be successfully predicted. More importantly, the results reveal that flow plays a dominant part in generating oriented crystal morphologies compared to other parameters, such as anisotropy strength, crystallization temperature, and physical noise.

  13. Preparation of AgCl Nano-Crystal Embedded Tellurite Nonlinear Optical Glasses under Electric Field Accompanied Heat Treatment

    Institute of Scientific and Technical Information of China (English)

    Jian LIN; Wenhai HUANG; Bofang LI; Chong JIN; Changcheng LIU; Shuhua LEI; Zhenrong SUN

    2008-01-01

    The quantum effect of nano-crystals is an important factor to improve nonlinear optical performance of nano-crystal embedded glasses,while controlling the size distribution and content of nano-crystals in the glass accurately is a key to obtain good quality.The auxiliary direct current electric field,accompanied with heat treatment,was applied on AgCl containing niobic tellurite glass sheet.The nucleation and crystallization of the glass were well controlled under auxiliary electric field.It was found that the average size of AgCl nano-crystal particles in the glass is smaller than that under single heat treatment,and the content of nano-crystals is higher.Therefore the third-order nonlinear optical performance of the glass was increased a lot.The local-area distributed AgCl nano-crystal particles can also be embedded into a glass sheet by using locally applied electric field.

  14. Spin-polarized spin-orbit-split quantum-well states in a metal film

    Energy Technology Data Exchange (ETDEWEB)

    Varykhalov, Andrei; Sanchez-Barriga, Jaime; Gudat, Wolfgang; Eberhardt, Wolfgang; Rader, Oliver [BESSY Berlin (Germany); Shikin, Alexander M. [St. Petersburg State University (Russian Federation)

    2008-07-01

    Elements with high atomic number Z lead to a large spin-orbit coupling. Such materials can be used to create spin-polarized electronic states without the presence of a ferromagnet or an external magnetic field if the solid exhibits an inversion asymmetry. We create large spin-orbit splittings using a tungsten crystal as substrate and break the structural inversion symmetry through deposition of a gold quantum film. Using spin- and angle-resolved photoelectron spectroscopy, it is demonstrated that quantum-well states forming in the gold film are spin-orbit split and spin polarized up to a thickness of at least 10 atomic layers. This is a considerable progress as compared to the current literature which reports spin-orbit split states at metal surfaces which are either pure or covered by at most a monoatomic layer of adsorbates.

  15. Electrostimulation of the magnetoplastic effect in LiF crystals by an "internal" electric field induced during indentation

    Science.gov (United States)

    Galustashvili, M. V.; Driaev, D. G.; Akopov, F. Kh.; Tsakadze, S. D.

    2013-08-01

    Indented LiF crystals demonstrate a change in the length of the dislocation rosette rays during their exposure to jointly acting dc magnetic and electric fields. It is shown that magnetic field with induction B = 1 T causes the electrostimulation or electrosuppression depending on the magnitude and direction of the external electric field with respect to the "internal" electric field induced by the charge transfer due to dislocations moving during the indentation.

  16. YbNi{sub 4}P{sub 2}. Single crystal growth by the Czochralski method and high-field magnetization measurements

    Energy Technology Data Exchange (ETDEWEB)

    Kliemt, Kristin; Krellner, Cornelius [Goethe-University, Frankfurt (Germany); Foerster, Tobias [HLD, Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Brando, Manuel [MPI for Chemical Physics of Solids, Dresden (Germany)

    2016-07-01

    We have investigated a new generation of YbNi{sub 4}P{sub 2} single crystals that were grown from a levitating melt by the Czochralski method. With T{sub C}= 0.17 K, this ferromagnetic material has the lowest Curie temperature ever observed among stoichiometric compounds. A quantum critical point occurs in the substitution series YbNi{sub 4}(P{sub 1-x}As{sub x}){sub 2} at x ∼ 0.1. The hybridization between localized f-electrons and the conduction electrons leads to a Fermi-liquid ground state with narrow bands and strongly enhanced effective electronic masses (heavy fermion system, Kondo temperature 8 K). An external magnetic field can split the bands, deform the Fermi surface and simultaneously suppress the Kondo interaction. If such a deformation changes the topology, it is called a Lifshitz transition. Previous thermodynamic and electrical transport studies have found indications for Lifshitz transitions in this Kondo lattice system. We report on results of high-field magnetization measurements at low temperature to further investigate the putative Lifshitz transitions in YbNi{sub 4}P{sub 2}.

  17. Ho{sup 3+} crystal-field levels, magnetic ordering, and magnetoelastic coupling in the chain nickelate Ho{sub 2}BaNiO{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Klimin, S.A., E-mail: klimin@isan.troitsk.ru [Institute of Spectroscopy RAS, 142190 Moscow, Troitsk (Russian Federation); Galkin, A.S. [Institute of Spectroscopy RAS, 142190 Moscow, Troitsk (Russian Federation); Technological Institute for Superhard and Novel Carbon Materials, 142190 Moscow, Troitsk (Russian Federation); Popova, M.N. [Institute of Spectroscopy RAS, 142190 Moscow, Troitsk (Russian Federation)

    2015-03-15

    Highlights: • First optical spectroscopic study of Ho{sub 2}BaNiO{sub 5} was done. • Quasi-doublet ground state of Ho{sup 3+} ion was found. • Magnetostriction driven change of the crystal field energies was observed. • Ho contribution into the heat capacity and magnetic susceptibility was calculated. - Abstract: Transmission spectroscopy data in wide spectral and temperature ranges are presented for Ho{sub 2}BaNiO{sub 5}. A quasi-doublet ground state of the non-Kramers Ho{sup 3+} ion, previously predicted theoretically, is confirmed experimentally for the first time. Its temperature-dependent splitting manifesting magnetic ordering at the Neél temperature T{sub N} = 49 K is discussed in the frame of the perturbation and mean-field approaches. Holmium contribution into the magnetic susceptibility χ(T) and specific heat C(T) is calculated using the spectroscopic data. The calculated contribution describes well experimental data available in literature. Analysis of shifts of the Ho{sup 3+} energy levels reveals magnetoelastic interactions in the antiferromagnetic state of Ho{sub 2}BaNiO{sub 5}.

  18. High-mobility field-effect transistors from large-area solution-grown aligned C60 single crystals.

    Science.gov (United States)

    Li, Hanying; Tee, Benjamin C-K; Cha, Judy J; Cui, Yi; Chung, Jong Won; Lee, Sang Yoon; Bao, Zhenan

    2012-02-08

    Field-effect transistors based on single crystals of organic semiconductors have the highest reported charge carrier mobility among organic materials, demonstrating great potential of organic semiconductors for electronic applications. However, single-crystal devices are difficult to fabricate. One of the biggest challenges is to prepare dense arrays of single crystals over large-area substrates with controlled alignment. Here, we describe a solution processing method to grow large arrays of aligned C(60) single crystals. Our well-aligned C(60) single-crystal needles and ribbons show electron mobility as high as 11 cm(2)V(-1)s(-1) (average mobility: 5.2 ± 2.1 cm(2)V(-1)s(-1) from needles; 3.0 ± 0.87 cm(2)V(-1)s(-1) from ribbons). This observed mobility is ~8-fold higher than the maximum reported mobility for solution-grown n-channel organic materials (1.5 cm(2)V(-1)s(-1)) and is ~2-fold higher than the highest mobility of any n-channel organic material (~6 cm(2)V(-1)s(-1)). Furthermore, our deposition method is scalable to a 100 mm wafer substrate, with around 50% of the wafer surface covered by aligned crystals. Hence, our method facilitates the fabrication of large amounts of high-quality semiconductor crystals for fundamental studies, and with substantial improvement on the surface coverage of crystals, this method might be suitable for large-area applications based on single crystals of organic semiconductors.

  19. Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

    Science.gov (United States)

    Lucovsky, Gerry; Wu, Kun; Pappas, Brian; Whitten, Jerry

    2013-04-01

    Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9>=n>3, and (TiO2)x(HfO2)1-x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii} local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding

  20. Near-field imaging of light propagation in photonic crystal waveguides: Explicit role of Bloch harmonics

    DEFF Research Database (Denmark)

    Bozhevolnyi, Sergey I.; Volkov, V.S.; Søndergaard, Thomas;

    2002-01-01

    We employ a collection scanning near-field optical microscope (SNOM) to image the propagation of light at telecommunication wavelengths along straight and bent regions of silicon-on-insulator photonic crystal waveguides (PCWs) formed by removing a single row of holes in the triangular 410-nm......-period lattice along the GammaM direction of the irreducible Brillouin zone. We obtain high quality SNOM images of PCWs excited in the wavelength range of 1520-1570 nm, which indicate good PCW mode confinement and low propagation loss. Using averaged cross sections of the intensity distributions before and after...... the interference between a quasihomogeneous background field and Bloch harmonics of the PCW mode, we account for spatial frequency spectra of the intensity variations and determine the propagation constant of the PCW mode at 1520 nm. The possibilities and limitations of SNOM imaging for the characterization...

  1. Extensional flow of nematic liquid crystal with an applied electric field

    KAUST Repository

    CUMMINGS, L. J.

    2013-10-17

    Systematic asymptotic methods are used to formulate a model for the extensional flow of a thin sheet of nematic liquid crystal. With no external body forces applied, the model is found to be equivalent to the so-called Trouton model for Newtonian sheets (and fibres), albeit with a modified \\'Trouton ratio\\'. However, with a symmetry-breaking electric field gradient applied, behaviour deviates from the Newtonian case, and the sheet can undergo finite-time breakup if a suitable destabilizing field is applied. Some simple exact solutions are presented to illustrate the results in certain idealized limits, as well as sample numerical results to the full model equations. Copyright © Cambridge University Press 2013.

  2. Nonlinear response and dynamical transitions in a phase-field crystal model for adsorbed overlayers

    Energy Technology Data Exchange (ETDEWEB)

    Ramos, J A P [Departamento de Ciencias Exatas, Universidade Estadual do Sudoeste da Bahia, 45000-000 Vitoria da Conquista, BA (Brazil); Granato, E [Laboratorio Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, 12245-970 Sao Jose dos Campos, SP (Brazil); Ying, S C; Ala-Nissila, T [Department of Physics, PO Box 1843, Brown University, Providence, RI 02912-1843 (United States); Achim, C V [Department of Applied Physics, Aalto University School of Science and Technology, PO Box 11000, FI-00076 Aalto, Espoo (Finland); Elder, K R, E-mail: Jorge@las.inpe.b [Department of Physics, Oakland University, Rochester, Michigan 48309-4487 (United States)

    2010-09-01

    The nonlinear response and sliding friction behavior of a phase-field crystal model for driven adsorbed atomic layers is determined numerically. The model describes the layer as a continuous density field coupled to the pinning potential of the substrate and under an external driving force. Dynamical equations which take into account both thermal fluctuations and inertial effects are used for numerical simulations of commensurate and incommensurate layers. At low temperatures, the velocity response of an initially commensurate layer shows hysteresis with dynamical melting and freezing transitions at different critical forces. The main features of the sliding friction behavior are similar to the results obtained previously from molecular dynamics simulations of particle models. However, the dynamical transitions correspond to nucleations of stripes rather than closed domains.

  3. Long-wavelength properties of phase-field-crystal models with second-order dynamics

    Science.gov (United States)

    Heinonen, V.; Achim, C. V.; Ala-Nissila, T.

    2016-05-01

    The phase-field-crystal (PFC) approach extends the notion of phase-field models by describing the topology of the microscopic structure of a crystalline material. One of the consequences is that local variation of the interatomic distance creates an elastic excitation. The dynamics of these excitations poses a challenge: pure diffusive dynamics cannot describe relaxation of elastic stresses that happen through phonon emission. To this end, several different models with fast dynamics have been proposed. In this article we use the amplitude expansion of the PFC model to compare the recently proposed hydrodynamic PFC amplitude model with two simpler models with fast dynamics. We compare these different models analytically and numerically. The results suggest that in order to have proper relaxation of elastic excitations, the full hydrodynamical description of the PFC amplitudes is required.

  4. Mean-Field Limit and Phase Transitions for Nematic Liquid Crystals in the Continuum

    Science.gov (United States)

    Bachmann, Sven; Genoud, François

    2017-08-01

    We discuss thermotropic nematic liquid crystals in the mean-field regime. In the first part of this article, we rigorously carry out the mean-field limit of a system of N rod-like particles as N→ ∞, which yields an effective `one-body' free energy functional. In the second part, we focus on spatially homogeneous systems, for which we study the associated Euler-Lagrange equation, with a focus on phase transitions for general axisymmetric potentials. We prove that the system is isotropic at high temperature, while anisotropic distributions appear through a transcritical bifurcation as the temperature is lowered. Finally, as the temperature goes to zero we also prove, in the concrete case of the Maier-Saupe potential, that the system converges to perfect nematic order.

  5. Nanoscale mechanical actuation and near-field read-out of photonic crystal molecules

    Science.gov (United States)

    Petruzzella, M.; La China, F.; Intonti, F.; Caselli, N.; De Pas, M.; van Otten, F. W. M.; Gurioli, M.; Fiore, A.

    2016-09-01

    We employed the contact forces induced by a near-field tip to tune and probe the optical resonances of a mechanically compliant photonic crystal molecule. Here, the pressure induced by the near-field tip is exploited to control the spectral proprieties of the coupled cavities in an ultrawide spectral range, demonstrating a reversible mode shift of 37.5 nm . Besides, by monitoring the coupling strength variation due to the vertical nanodeformation of the dielectric structure, distinct tip-sample interaction regimes have been unambiguously reconstructed with a nano-Newton sensitivity. These results demonstrate an optical method for mapping mechanical forces at the nanoscale with a lateral spatial resolution below 100 nm.

  6. Bicritical universality of the anisotropic Heisenberg model in a crystal field.

    Science.gov (United States)

    Freire, R T S; Plascak, J A

    2015-03-01

    The bicritical properties of the three-dimensional classical anisotropic Heisenberg model in a crystal field are investigated through extensive Monte Carlo simulations on a simple cubic lattice, using Metropolis and Wolff algorithms. Field-mixing and multidimensional histogram techniques were employed in order to compute the probability distribution function of the extensive conjugate variables of interest and, using finite-size scaling analysis, the first-order transition line of the model was precisely located. The fourth-order cumulant of the order parameter was then calculated along this line and the bicritical point located with good precision from the cumulant crossings. The bicritical properties of this point were further investigated through the measurement of the universal probability distribution function of the order parameter. The results lead us to conclude that the studied bicritical point belongs in fact to the three-dimensional Heisenberg universality class.

  7. Sternheimer Factors and Electric-Field-Gradient Hyperpolarisabilities for Ions in Crystals

    Science.gov (United States)

    Fowler, P. W.; Kelly, H. M.

    1994-02-01

    Analytic coupled Hartree-Fock calculations of the electric field gradient response properties y (the Sternheimer shielding factor) and e (the dipole-dipole-electric field gradient hyperpolarisability) have been carried out on anions in clusters that simulate that crystal environment. The systems studied are F- in LiF and NaF, Cl- in LiCl and NaCl, O2-in MgO, S2- in MgS, and H- in LiH. Both properties show large reductions from free-ion values and significant variation with lattice parameter, and the results indicate that damped values of anion Sternheimer factors will be necessary in accurate simulation of N Q R data or modelling of properties of ion-pairs.

  8. Nonlinear behavior analysis of split-winding dry-type transformer using a new star model and a coupled field-circuit approach

    Directory of Open Access Journals (Sweden)

    Azizian Davood

    2016-12-01

    Full Text Available Regarding the importance of short circuit and inrush current simulations in the split-winding transformer, a novel nonlinear equivalent circuit is introduced in this paper for nonlinear simulation of this transformer. The equivalent circuit is extended using the nonlinear inductances. Employing a numerical method, leakage and magnetizing inductances in the split-winding transformer are extracted and the nonlinear model inductances are estimated using these inductances. The introduced model is validated and using this nonlinear model, inrush and short-circuit currents are calculated. It has been seen that the introduced model is valid and suitable for simulations of the split-winding transformer due to various loading conditions. Finally, the effects of nonlinearity of the model inductances are discussed in the following.

  9. Large piezoelectricity in electric-field modified single crystals of SrTiO3

    Science.gov (United States)

    Khanbabaee, B.; Mehner, E.; Richter, C.; Hanzig, J.; Zschornak, M.; Pietsch, U.; Stöcker, H.; Leisegang, T.; Meyer, D. C.; Gorfman, S.

    2016-11-01

    Defect engineering is an effective and powerful tool to control the existing material properties and produce completely new ones, which are symmetry-forbidden in a defect-free crystal. For example, the application of a static electric field to a single crystal of SrTiO3 forms a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. While it was previously shown that this near-surface phase holds pyroelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO3, this paper reports that the same phase is strongly piezoelectric. We demonstrate the piezoelectricity of this phase through stroboscopic time-resolved X-ray diffraction under alternating electric field and show that the effective piezoelectric coefficient d33 ranges between 60 and 100 pC/N. The possible atomistic origins of the piezoelectric activity are discussed as a coupling between the electrostrictive effect and spontaneous polarization of this near-surface phase.

  10. Precise Patterning of Organic Single Crystals via Capillary-Assisted Alternating-Electric Field.

    Science.gov (United States)

    Zhang, Yedong; Jie, Jiansheng; Sun, Yuning; Jeon, Seok-Gy; Zhang, Xiujuan; Dai, Gaole; Lee, Cheol Jin; Zhang, Xiaohong

    2017-07-01

    Owing to the extraordinary properties, organic micro/nanocrystals are important building blocks for future low-cost and high-performance organic electronic devices. However, integrated device application of the organic micro/nanocrystals is hampered by the difficulty in high-throughput, high-precision patterning of the micro/nanocrystals. In this study, the authors demonstrate, for the first time, a facile capillary-assisted alternating-electric field method for the large-scale assembling and patterning of both 0D and 1D organic crystals. These crystals can be precisely patterned at the photolithography defined holes/channels at the substrate with the yield up to 95% in 1 mm(2) . The mechanism of assembly kinetics is systematically studied by the electric field distribution simulation and experimental investigations. By using the strategy, various organic micro/nanocrystal patterns are obtained by simply altering the geometries of the photoresist patterns on substrates. Moreover, ultraviolet photodetectors based on the patterned Alq3 micro/nanocrystals exhibit visible-blind photoresponse with high sensitivity as well as excellent stability and reproducibility. This work paves the way toward high-integration, high-performance organic electronic, and optoelectronic devices from the organic micro/nanocrystals. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Fluctuations in the Microwave Conductivity of YBCO Single Crystals in Zero DC Magnetic Field

    Science.gov (United States)

    Anlage, Steven; Mao, Jian; Booth, James; Wu, Dong-Ho; Peng, J. L.

    1996-03-01

    We present a quantitative analysis of finite frequency fluctuation conductivity above and below Tc in cuprate superconductors in zero dc magnetic field.(S. M. Anlage, J. Mao, J. C. Booth, D. H. Wu, and J. L. Peng, Phys. Rev. B 53), Feb. 1, 1996. In a YBa_2Cu_3O_7-δ crystal showing a linear in temperature increase of the magnetic penetration depth at low temperatures, we find that two-dimensional finite-frequency Gaussian conductivity fluctuations above Tc cross over into a slower divergence of the conductivity as Tc is approached from above. We find that the critical regime above Tc is less than about 0.6 K wide, although inhomogeneities in the crystal may also dominate the conductivity in this temperature range. At and below T_c, 3D fluctuations dominate the conductivity, with evidence of 3D XY critical scaling of the imaginary part of the conductivity down to 5 K below T_c. Supported by the NSF NYI program (DMR-9258183), and NSF grant DMR-9123198.

  12. Exchange and crystal field in Sm-based magnets. II. Phenomenological analysis and density functional calculations

    Science.gov (United States)

    Kuz'Min, Michael D.; Steinbeck, Lutz; Richter, Manuel

    2002-02-01

    A technique of determining the exchange field Bex on the 4f shell of Sm atoms in Sm-based magnets is proposed. It makes use of the 4f intermultiplet transition in Sm, observed in inelastic neutron scattering (INS) experiments. The method is used to analyze previously published data for a number of Sm-Fe and Sm-Co intermetallics, for all of which Bex is determined. Additional information on intramultiplet transitions in SmCo5 and Sm2Co17 makes it possible to obtain more accurate Bex values as well as to estimate the leading crystal field parameter (CFP) A02 for these compounds. For the same systems an independent determination of A02 is carried out using published magnetization curves and the Bex values found from the INS spectra. The two ``experimental'' values of A02 (INS and magnetization) agree well. For comparison, theoretical Sm-Co exchange fields and CFP for SmCo5 and Sm2Co17 are obtained from full-potential density-functional calculations. The theoretical A02 are shifted toward more negative values with respect to their experimental counterparts by a few millielectronvolts. The calculated Sm-Co exchange fields are in fair agreement with the experimentally determined values of the total exchange field on Sm, Bex, the weak Sm-Sm exchange interaction being accountable for the remaining small discrepancies.

  13. Synchrotron radiation topographic observation of KTiOPO4 crystals under an electric field

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    In situ white-beam synchrotron radiation topographic observations under an electric field have been made on the KTiOPO4(KTP) family of crystals.The investigation shows a strong enhancement of diffracted intensity for hkl reflections(l≠0) and topographic contrast in the form of fine striations when the external electric field is parallel to the polar axis.Severalk kinds of doped and undoped samples with various grown-in defects,such as domain boundaries.growth striations,growth-sector boundaries.dislocations.etc.,have been studied in detail.The results suggest that these defects have very little effect on the field-induced striations,It is believed that the movement of K+ ions driven by the electric field leads to a local accumulation of charges and a lattice distortion.The stronly anisotropic conductivity is a governing factor in the explanation of the field-related phenomena in this kind of quasi-one-dimensional conductor.

  14. Application of magnetically-perturbed time-dependent density functional theory to magnetic circular dichroism. IV. The influence of zero-field splitting on the spectra of S > 1/2 molecules

    Energy Technology Data Exchange (ETDEWEB)

    Seth, Michael, E-mail: mseth@ucalgary.ca [Department of Chemistry, University of Calgary, University Drive 2500, Calgary, AB T2N-1N4 (Canada); Ziegler, Tom, E-mail: ziegler@ucalgary.ca [Department of Chemistry, University of Calgary, University Drive 2500, Calgary, AB T2N-1N4 (Canada)

    2012-02-20

    The theory of calculating magnetic circular dichroism in the presence of zero-field splitting is presented and illustrated with applications to small and medium-sized systems. Highlights: Black-Right-Pointing-Pointer ZFS and MCD calculated with DFT are combined. Black-Right-Pointing-Pointer Influence of ZFS on the MCD spectra of group 15 hydrides analyzed. Black-Right-Pointing-Pointer Absorption and MCD spectra of Fe-EDTA-peroxide complex calculated. Black-Right-Pointing-Pointer ZFS does not appear to influence MCD spectra qualitatively. Black-Right-Pointing-Pointer Quantitative effects are present and difficult to model. - Abstract: An implementation into the ADF program of a method for calculating zero-field splitting (ZFS) of molecules with spin degenerate ground states and S > 1/2 is reported. ZFS can influence temperature-dependent magnetic circular dichroism (MCD) intensity. Previously published equations for the calculation of MCD with time-dependent density functional theory are modified to take zero-field splitting into account. The MCD spectra of the group 15 hydrides and the complex formed from iron (III), ethylenediaminetetraacetate and peroxide, [Fe(III)(EDTA)O{sub 2}]{sup 3-} are simulated. These spectra are analyzed with particular reference to the influence of ZFS on the MCD intensity.

  15. High-resolution magnetic field imaging with a nitrogen-vacancy diamond sensor integrated with a photonic-crystal fiber.

    Science.gov (United States)

    Fedotov, I V; Blakley, S M; Serebryannikov, E E; Hemmer, P; Scully, M O; Zheltikov, A M

    2016-02-01

    We demonstrate high-resolution magnetic field imaging with a scanning fiber-optic probe which couples nitrogen-vacancy (NV) centers in diamond to a high-numerical-aperture photonic-crystal fiber integrated with a two-wire microwave transmission line. Magnetic resonance excitation of NV centers driven by the microwave field is read out through optical interrogation through the photonic-crystal fiber to enable high-speed, high-sensitivity magnetic field imaging with sub 30 μm spatial resolution.

  16. Influence of spin-orbit interactions on the cubic crystal-field states of the d4 system*

    OpenAIRE

    Radwanski, R. J.; Ropka, Z.

    2002-01-01

    It has been shown that for the highly-correlated d4 electronic system the spin-orbit interactions produce, even in case of the cubic crystal-field interactions, a singlet ground state. Its magnetic moment grows rapidly with the applied magnetic field approaching 4 uB for the Eg state, but only 3 uB for the T2g state. The applicability of the present results to the Mn3+ ion in LaMnO3 is discussed. Keywords: crystal-field, spin-orbit, orbital moment. PACS: 71.70.E, 75.10.D

  17. In-Situ Alignment of MnBi Crystals Induced by High Magnetic Field above Curie Temperature

    Institute of Scientific and Technical Information of China (English)

    LIU Yong-Sheng; ZHANG Jin-Cang; REN Zhong-Ming; CAO Shi-Xun

    2007-01-01

    @@ Above Curie temperature, MnBi crystals are aligned in situ along the c-axis in a Bi matrix by a high fabrication magnetic field Hf of 10 T. Magnetic testing shows a pronounced anisotropy in magnetization in directions normal and parallel to the fabrication field, resulting from the alignment. The successful alignment may result from the fact that the easy magnetization direction is along the c-axis of MnBi and the high fabrication field of 10 T is large enough to rotate the MnBi crystal to this direction even though the temperature is above the Curie temperature.

  18. A Photonic Crystal Magnetic Field Sensor Using a Shoulder-Coupled Resonant Cavity Infiltrated with Magnetic Fluid.

    Science.gov (United States)

    Su, Delong; Pu, Shengli; Mao, Lianmin; Wang, Zhaofang; Qian, Kai

    2016-12-16

    A kind of photonic crystal magnetic field sensor is proposed and investigated numerically. The shoulder-coupled resonant cavity is introduced in the photonic crystal, which is infiltrated with magnetic fluid. Through monitoring the shift of resonant wavelength, the magnetic field sensing is realized. According to the designed infiltration schemes, both the magnetic field sensitivity and full width at half maximum increase with the number of infiltrated air holes. The figure of merit of the structure is defined to evaluate the sensing performance comprehensively. The best structure corresponding to the optimal infiltration scheme with eight air holes infiltrated with magnetic fluid is obtained.

  19. Properties of the ground state in a spin-2 transverse Ising model with the presence of a crystal field

    Institute of Scientific and Technical Information of China (English)

    姜伟; 魏国柱; 杜安; 张起

    2002-01-01

    The properties of the ground state in the spin-2 transverse Ising model with the presence of a crystal field arestudied by using the effective-field theory with correlations. The longitudinal and transverse magnetizations, the phasediagram and the internal energy in the ground state are given numerically for a honeycomb lattice (z=3).

  20. Viewing angle switching of liquid crystal display using fringe-field switching to control off-axis phase retardation

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Young Jin; Kim, Jin Ho; Her, Jung Hwa; Lee, Seung Hee [Polymer BIN Fusion Research Center, Department of Polymer Nano-Science and Technology, Chonbuk National University, Chonju, Chonbuk 561-756 (Korea, Republic of); Park, Kyoung Ho; Lee, Joun Ho; Kim, Byeong Koo [Mobile Product Development Department, LG Display Company, Ltd, Gumi, Gyungbuk 730-350 (Korea, Republic of); Kang, Wan-Seok; Lee, Gi-Dong, E-mail: gdlee@dau.ac.k, E-mail: lsh1@chonbuk.ac.k [Department of Electronics Engineering, Dong-A University, Pusan 604-714 (Korea, Republic of)

    2010-03-03

    A viewing angle switchable liquid crystal display associated with fringe-field switching mode is proposed. In the device, one pixel is composed of a main pixel and a sub-pixel, in which both pixels are formed to generate a fringe electric field. However, the field directions are different from each other so that in the main pixel, the fringe field rotates the liquid crystal for displaying the main image, whereas it controls only the tilt angle of the liquid crystal without rotating in the sub-pixel region. In this way, phase retardation to cause leakage of light at the off-normal axis can be generated in the sub-pixel, and by utilizing the light, the main displayed image in the normal direction can be blocked in the oblique viewing direction.