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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Effect of intramolecular interaction on time growth of second moment of multiple quantum NMR in solids
Место публикации : INTERNATIONAL CONFERENCE ON RESONANCES IN CONDENSED MATTER: ALTSHULER100. Ser. Journal of Physics Conference Series: IOP PUBLISHING LTD, 2011. - Vol. 324: International Conference on Resonances in Condensed Matter (JUN 21-25, 2011, Kazan, RUSSIA). - Ст.12010. - ISBN 1742-6588, DOI 10.1088/1742-6596/324/1/012010
Примечания : Cited References: 12
Предметные рубрики: COHERENCES
DYNAMICS
Ключевые слова (''Своб.индексиров.''): dipole dipole interactions--double-quantum--intramolecular interactions--multiple quantum nmr--nuclear spin system--quantum spectrum--rate increase--second moments--solids containing methyl groups--time dependence--functional groups--quantum optics--solids--spin dynamics--hamiltonians
Аннотация: The time dependence of the NMR multiple quantum spectrum in solids containing methyl groups is investigated. We studied both of types of the nuclear spin systems: namely linking by secular part of the mutual dipole-dipole interaction and linking by effective double quantum Hamiltonian. It is revealed for the first type of systems the rate with the time of the growing up of the second moment when intramolecular interaction is present becomes less in compare with situation when a strong intramolecular interaction is absent. On the contrary for the second type of Hamiltonian the above rate increases.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Polukhin D. S.
Заглавие : Effects of cross correlations between inhomogeneities of the parameters of an isotropic medium on the spectrum and damping of elastic waves
Коллективы :
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 110, Is. 2. - P345-359. - ISSN 1063-7761, DOI 10.1134/S1063776110020184
Примечания : Cited References: 17. - This study was supported in part by the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools (grant no. 3818.2008.3) and the Presidium of the Russian Academy of Sciences (program no. 27.1) and performed within the framework of the Federal Target Program (State Contract no. 02.740.11.0220).
Ключевые слова (''Своб.индексиров.''): cross correlations--dispersion law--elastic force--inhomogeneities--isotropic medium--negative cross-correlation--physical nature--two parameter--wave spectra--damping--dispersions--elastic waves--hamiltonians--dispersion (waves)
Аннотация: The dispersion and damping laws have been investigated for elastic waves in an isotropic medium with one- and three-dimensional inhomogeneities of the density p(x) of the material and the elastic force constants mu(x) and lambda(x) with allowance for the cross correlations between these inhomogeneities. It has been demonstrated that the positive cross correlations between mu(x) and lambda(x), as well as the negative cross correlations between p(x) and mu(x) or p(x) and lambda(x), lead to an enhancement of the modification of the dispersion law and an increase in the damping of waves. The positive cross correlations between p(x) and mu(x) or p(x) and lambda(x), as well as the negative cross correlations between mu(x) and lambda(x), result in the opposite effects: a weakening of the modification of the dispersion law and a decrease in the damping. An analysis of the results obtained in this paper and in our recent work [15] has made it possible to formulate the general regularity of the effects of cross correlations, irrespective of the physical nature of the waves: the effects of cross correlations between inhomogeneities of any two parameters of the material on the wave spectrum depend on whether both parameters related by the cross correlations belong to the same part of the Hamiltonian (i.e., if they both belong to either the kinetic part or the potential part of the Hamiltonian) or they belong to different parts of the Hamiltonian. The positive cross correlations lead to a greater modification of the dispersion law and to an increase in the damping of waves in the former case and to a decrease in these characteristics in the latter case. Correspondingly, the negative cross correlations in each of these cases result in the opposite effects. This regularity has been explained qualitatively.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Zamkova N. G.
Заглавие : Ab initio calculation of the ferroelectric phase transition in disordered and ordered PbSc0.5Ta0.5O3 and PbSc0.5Nd0.5O3 solid solutions with the use of a model Hamiltonian
Разночтения заглавия :авие SCOPUS: Ab initio calculation of the ferroelectric phase transition in disordered and ordered PbSc0.5Ta0.5O3 and PbSc 0.5Nd0.5O3 solid solutions with the use of a model Hamiltonian
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 106, Is. 3. - P542-549. - ISSN 1063-7761, DOI 10.1134/S1063776108030138
Примечания : Cited References: 17
Предметные рубрики: RELAXOR FERROELECTRICS
PEROVSKITES
BATIO3
PBTIO3
Ключевые слова (''Своб.индексиров.''): approximation theory--ferroelectric materials--hamiltonians--mathematical models--monte carlo methods--phase transitions--ferroelectric phase transition--gordon-kim model--local-mode approximation--solid solutions
Аннотация: To describe the ferroelectric phase transition in ordered and disordered PbSc0.5Ta0.5O3 (PST) and PbSc0.5Nd0.5O3 (PSN) solid solutions, a model Hamiltonian is written in the local-mode approximation, in which long-range dipole-dipole and short-range interactions of local modes are taken into account. The Hamiltonian parameters are determined from the set of energies of a series of distorted structures, calculated within the nonempirical generalized Gordon-Kim model. The statistical mechanics of the systems with a model Hamiltonian is investigated by the Monte Carlo method. It is revealed that PSN solid solutions undergo a transition to the ferroelectric rhombohedral phase through an intermediate phase, existing in a narrow temperature range. PST solid solutions undergo a ferroelectric phase transition directly from the paraelectric cubic to the ferroelectric rhombohedral phase.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Orlov Yu. S.
Заглавие : Covalence-induced stabilization of an intermediate-spin state and the magnetic susceptibility of LaCoO3
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 104, Is. 3. - P436-444. - ISSN 1063-7761, DOI 10.1134/S1063776107030090
Примечания : Cited References: 24. - This work was supported by the program of the Division of Physical Sciences of the Russian Academy of Sciences “Strong Electronic Correlations,” the integration project SORAN-URORAN (grant no. 74), and the Krasnoyarsk krai Science Foundation
Предметные рубрики: TRANSITION
Ключевые слова (''Своб.индексиров.''): band structure--electron transitions--ground state--hamiltonians--magnetic susceptibility--magnetic variables measurement--spin dynamics--covalence induced stabilization--diagnoalization--orbital degeneracy--spin states--lanthanum compounds
Аннотация: The energies of terms with spins S = 0, 1, 2 have been found using exact diagonalization of the multielectron Hamlitonian of a multiband pd model for the CoO6 cluster. Co (e(g) orbital)-O hops, which form the covalent sigma bond, are shown to decrease the energy of the state (IS) with an intermediate spin (S = 1) as compared to the energy of the state (LS) with a low spin (S = 0). An analogue of the Tanabe-Sugano diagram that takes into account the covalence of the CoO6 cluster is constructed. The state with S = 1 is shown to be a ground state at certain model parameters. An increase in temperature is established to decrease the crystal field and, thus, favors the transition of the ground state from LS to IS at T = 100 K and the transition of the IS ground state to a state (HS) with a high spin (S = 2) at T = 550 K. The magnetic susceptibility of LaCoO3 is calculated with allowance for the LS, IS, and HS states and for the fact that the HS state exhibits threefold orbital degeneracy of the t(2g) shell, which results in an effective orbital moment L = 1 and the importance of spin-orbit interaction. The behavior of this magnetic susceptibility agrees well with the experimental chi(T) dependence of LaCoO3.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G., Sherman A. V.
Заглавие : Effective Hamiltonian and the properties of normal and superconductive phases of n-type cuprates
Место публикации : Physica B: ELSEVIER SCIENCE BV, 2005. - Vol. 359: International Conference on Strongly Correlated Electron Systems (SCES 04) (JUL 26-30, 2004, Karlsruhe, GERMANY). - P521-523. - ISSN 0921-4526, DOI 10.1016/j.physb.2005.01.134
Примечания : Cited References: 13
Предметные рубрики: MODEL
SYMMETRY
Ключевые слова (''Своб.индексиров.''): strong electron correlations--superconductivity--multiband p-d model--n-type cuprates--multiband p-d model--n-type cuprates--strong electron correlations--superconductivity--antiferromagnetism--correlation theory--fermi surface--hamiltonians--mathematical models--microscopic examination--oxide superconductors--phase diagrams--semiconductor doping--generalized tight-binding (gtb)--multiband p-d models--n-type cuprates--single electron correlations--superconductivity
Аннотация: In the framework of the effective low-energy model for high-T-c, cuprates with account for three-center interaction terms and spin fluctuations the properties of normal and superconducting phases of n-type cuprates are investigated. Microscopic model parameters were obtained from ARPES data in undoped compounds. Obtained evolution of the chemical potential with doping, Fermi surface at optimal doping, and T-c(x) phase diagram are in remarkably good agreement with the experiment. (c) 2005 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Rotter I., Sadreev A. F.
Заглавие : Zeros in single-channel transmission through double quantum dots
Место публикации : Phys. Rev. E: AMERICAN PHYSICAL SOC, 2005. - Vol. 71, Is. 4. - Ст.46204. - ISSN 1063-651X, DOI 10.1103/PhysRevE.71.046204
Примечания : Cited References: 28
Предметные рубрики: PHASE EVOLUTION
RESONANCE
TRANSPORT
SYSTEMS
Ключевые слова (''Своб.индексиров.''): fano interference--fano resonances--overlapping resonances--transmission amplitude--channel capacity--eigenvalues and eigenfunctions--function evaluation--hamiltonians--mathematical models--mathematical operators--matrix algebra--resonance--signal interference--semiconductor quantum dots
Аннотация: By using a simple model we consider single-channel transmission through a double quantum dot that consists of two single dots coupled by a wire of finite length L. Each of the two single dots is characterized by a few energy levels only, and the wire is assumed to have only one level whose energy depends on the length L. The transmission is described by using S matrix theory and the effective non-Hermitian Hamilton operator H-eff of the system. The decay widths of the eigenstates of H-eff depend strongly on energy. The model explains the origin of the transmission zeros of the double dot that is considered by us. Mostly, they are caused by (destructive) interferences between neighboring levels and are of first order. When, however, both single dots are identical and their transmission zeros are of first order, those of the double dot are of second order. First-order transmission zeros cause phase jumps of the transmission amplitude by pi, while there are no phase jumps related to second-order transmission zeros. In this latter case, a phase jump occurs due to the fact that the width of one of the states vanishes when crossing the energy of the transmission zero. The parameter dependence of the widths of the resonance states is determined by the spectral properties of the two single dots.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Rotter I., Sadreev A. F.
Заглавие : Avoided level crossings, diabolic points, and branch points in the complex plane in an open double quantum dot
Место публикации : Phys. Rev. E: AMERICAN PHYSICAL SOC, 2005. - Vol. 71, Is. 3. - Ст.36227. - ISSN 1063-651X, DOI 10.1103/PhysRevE.71.036227
Примечания : Cited References: 49
Предметные рубрики: BERRY TOPOLOGICAL PHASE
EXCEPTIONAL POINTS
GEOMETRIC PHASES
NUCLEAR REACTIONS
RESONANCE STATES
UNIFIED THEORY
S-MATRIX
CONTINUUM
REPULSION
INTERFEROMETER
Ключевые слова (''Своб.индексиров.''): branch points in the complex plane (bpcp)--diabolic points (dp)--geometric phases--riemann sheets--eigenvalues and eigenfunctions--electron energy levels--functions--hamiltonians--quantum theory--resonance--topology--semiconductor quantum dots
Аннотация: We study the spectrum of an open double quantum dot as a function of different system parameters in order to receive information on the geometric phases of branch points in the complex plane (BPCP). We relate them to the geometrical phases of the diabolic points (DPs) of the corresponding closed system. The double dot consists of two single dots and a wire connecting them. The two dots and the wire are represented by only a single state each. The spectroscopic values follow from the eigenvalues and eigenfunctions of the Hamiltonian describing the double dot system. They are real when the system is closed, and complex when the system is opened by attaching leads to it. The discrete states as well as the narrow resonance states avoid crossing. The DPs are points within the avoided level crossing scenario of discrete states. At the BPCP, width bifurcation occurs. Here, different Riemann sheets evolve and the levels do not cross anymore. The BPCP are physically meaningful. The DPs are unfolded into two BPCP with different chirality when the system is opened. The geometric phase that arises by encircling the DP in the real plane, is different from the phase that appears by encircling the BPCP. This is found to be true even for a weakly opened system and the two BPCP into which the DP is unfolded.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Shneider E. I.
Заглавие : Effective Hamiltonian for HTSC cuprates taking into account electron-phonon interaction in the strong-correlation regime
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 101, Is. 5. - P844-855. - ISSN 1063-7761, DOI 10.1134/1.2149064
Примечания : Cited References: 38. - This work was supported by the Russian Foundation for Basic Research (project no. 03-02-16124), the program “Quantum Macrophysics” of the Presidium of the Russian Academy of Sciences, the Foundation in Support for Russian Science, the Foundation of Noncommercial
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
D-WAVE SUPERCONDUCTIVITY
T-C
DISPERSION
SCATTERING
OXIDES
STATE
MODEL
Ключевые слова (''Своб.индексиров.''): electron beams--electronic structure--optimization--phonons--electron correlations--hubbard x operators--spin-photon interaction--hamiltonians
Аннотация: Electron-phonon interaction is sequentially derived from a realistic p-d multiband model for the cuprates under conditions of strong electron correlations. The electronic structure is described using the representation of the Hubbard X operators in a generalized tight-binding method. Dependences of the diagonal and off-diagonal (on lattice sites) matrix elements of electron-phonon interaction on the wavevectors are found for three phonon modes, namely, breathing, apical breathing, and bending modes. The interactions of the breathing and bending modes with electrons are shown to contribute to the formation of kinks in the (0; 0)-(pi; pi) and (0; 0)-(pi; 0) directions, respectively. A low-energy t-J* model with phonons is developed; apart from electron-phonon interaction, it also includes spin-phonon interaction. The elimination of phonons gives an effective electron-electron interaction that depends on the occupation number of a multielectron term and on the carrier concentration due to strong electron correlations. (c) 2005 Pleiades Publishing, Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : The electron energy spectrum and superconducting transition temperature of strongly correlated fermions with three-center interactions
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 100, Is. 3. - P608-616. - ISSN 1063-7761, DOI 10.1134/1.1901772
Примечания : Cited References: 29
Предметные рубрики: T-J MODEL
BAND HUBBARD-MODEL
VALENCE BOND STATE
RANGE-ORDER
SYSTEMS
WAVE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--approximation theory--fermions--ground state--hamiltonians--superconductivity--density of states--electron energy spectrum--strongly correlated fermions--superconducting phase--superconducting transition temperature
Аннотация: The renormalizations of the fermionic spectrum are considered within the framework of the t-J* model taking into account three-center interactions (H-(3)) and magnetic fluctuations. Self-consistent spin dynamics equations for strongly correlated fermions with three-center interactions were obtained to calculate quasi-spin correlators. A numerical self-consistent solution to a system of ten equations was obtained to show that, in the nearest-neighbor approximation, simultaneously including H-(3) and magnetic fluctuations at n n(1) (n(1) approximate to 0.72 for 2t/U = 0.25) caused qualitative changes in the structure of the energy spectrum. A new Van Hove singularity is then induced in the density of states, and an additional maximum appears in the T-c(n) concentration dependence of the temperature of the transition to the superconducting phase with order parameter symmetry of the d(x2-y2) type. (C) 2005 Pleiades Publishing, Inc.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bulgakov E. N., Sadreev A. F.
Заглавие : Statistics of wave functions and currents induced by spin-orbit interaction in chaotic billiards
Место публикации : Phys. Rev. E: AMER PHYSICAL SOC, 2004. - Vol. 70, Is. 5. - Ст.56211. - ISSN 1539-3755, DOI 10.1103/PhysRevE.70.056211
Примечания : Cited References: 33
Предметные рубрики: HELMHOLTZ-EQUATION
PERSISTENT CURRENTS
ELECTRON-GAS
RINGS
EIGENFUNCTIONS
SYSTEMS
PHASE
Ключевые слова (''Своб.индексиров.''): approximation theory--chaos theory--degrees of freedom (mechanics)--eigenvalues and eigenfunctions--electric field effects--electric potential--electron gas--hamiltonians--heterojunctions--microwaves--statistical methods--chaotic robnik billiards--current distributions--spin-orbit interaction (soi)--wave functions--quantum theory
Аннотация: We show that the wave function and current statistics in chaotic Robnik billiards crucially depend on the constant of the spin-orbit interaction (SOI). For small constant the current statistics is described by universal current distributions derived for slightly opened chaotic billiards [Saichev et al. J. Phys. A. 35, L87 (2002)] although one of the components of the spinor eigenfunctions is not universal. For strong SOI both components of the spinor eigenstate are complex random Gaussian fields. This observation allows us to derive the distributions of spin-orbit persistent cut-rents which well describe numerical statistics. For intermediate values of the statistics of the eigenstates and currents, both are deeply nonuniversal.
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