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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Popkov S. I., Shaikhutdinov K. A., Petrov M. I.
Заглавие : Mechanisms of dissipation in a Josephson medium based on a high-temperature superconductor in a magnetic field
Разночтения заглавия :авие SCOPUS: Mechanisms of dissipation in a josephson medium based on a high-temperature superconductor in a magnetic field
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 48, Is. 5. - P826-832. - ISSN 1063-7834, DOI 10.1134/S1063783406050039
Примечания : Cited References: 32
Предметные рубрики: RESISTIVE TRANSITION
PHASE-SLIP
TRANSPORT-PROPERTIES
MAGNETORESISTANCE
SYSTEM
MODEL
YBA2CU3O7-X
PENETRATION
COMPOSITES
HYSTERESIS
Аннотация: This paper reports on the results of an investigation into the influence of magnetic fields (0-60 kOe) on the temperature dependences of the electrical resistance R(T) of the Y3/4Lu1/4Ba2Cu3O7 + CuO composites. The structure of these composites is considered to be a network of tunnel-type Josephson junctions in which a nonsuperconducting component (CuO) forms boundaries (barriers) between high-temperature superconducting crystallites. The temperature dependence R(T) of the composites has two steps characteristic of granular superconductors: (i) an abrupt change in the electrical resistance at the critical temperature of high-temperature superconducting crystallites and (ii) a smooth transition to the superconducting state under the influence of the boundaries between the crystallites. The experimental dependences R(T) are analyzed within the Ambegaokar-Halperin model of thermal fluctuations in Josephson junctions and the flux creep model. An increase in the magnetic field leads to a crossover from the Ambegaokar-Halperin mechanism to the flux creep mechanism. The temperature dependences R(T) in the range of weak magnetic fields (from 0 to 10(2) Oe) are adequately described by the relationship following from the Ambegaokar-Halperin model. In the range of strong magnetic fields (from 10(3) to 6 x 10(4) Oe), the dissipation obeys the Arrhenius law R similar to exp(-U(H)/T)], which is characteristic of the flux creep model with a temperature-independent pinning energy U(H). The effective Josephson coupling energies and the pinning energies corresponding to the Ambegaokar-Halperin and flux creep mechanisms are determined.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Popkov S. I., Shaihutdinov K. A., Petrov M. I.
Заглавие : The mechanisms responsible for broadening of the resistive transition under magnetic field in the Josephson junction network realized in bulk YBCO+CuO composites
Коллективы : International Workshop on Weak Superconductivity
Разночтения заглавия :авие SCOPUS: The mechanisms responsible for broadening of the resistive transition under magnetic field in the Josephson junction network realized in bulk YBCO + CuO composites
Место публикации : Physica C. - 2006. - Vol. 435, Is. 1-2. - P.12-15. - ISSN 0921-4534, DOI 10.1016/j.physc.2006.01.008
Примечания : Cited References: 15
Предметные рубрики: SUPERCONDUCTORS
MODEL
Ключевые слова (''Своб.индексиров.''): josephson network--ybco plus cuo composites--dissipation--magnetic field--dissipation--josephson network--magnetic field--ybco + cuo composites--composite materials--copper compounds--mathematical models--phase transitions--semiconductor junctions--yttrium compounds--creep model--josephson network--ybco + cuo composites--magnetic field effects
Аннотация: The experimental results of the effect of the magnetic field (up to 60 kOe) on the broadening of the resistive transition of bulk composites Y3/4Lu1/4Ba2CU3O7 (YBCO) + CuO are presented. These composites represent the network of the tunnel-type Josephson junctions where the copper oxide acts as a material forming barriers between YBCO crystallites. The mechanisms responsible for broadening of the resistive transition under magnetic field are discussed. The analysis of experimental R(7) dependences have shown that in the low field range 0-10(2) Oe, the R(7) dependences are described well by the Ambegaokar-Halperin (AH) model. In the range 10(3)-6 x 10(4) Oe, the dissipation follows Arrhenius law R similar to exp(-U(H)/k(B)T) characteristic for thermally activated flux creep model. In the range H similar to 10(2)-10(3), the crossover from AH to flux creep dissipation mechanisms occurs. (c) 2006 Elsevier B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G., Yakimov L. E.
Заглавие : The role of orbital ordering in the formation of electron structure in undoped LaMnO3 manganites in the regime of strong electron correlations
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 6. - P972-985. - ISSN 1063-7761, DOI 10.1134/S1063776106060112
Примечания : Cited References: 25
Предметные рубрики: COLOSSAL MAGNETORESISTIVE OXIDES
DOUBLE EXCHANGE
BAND
MODEL
Ключевые слова (''Своб.индексиров.''): computational methods--correlation methods--doping (additives)--electrons--ferromagnetic materials--lanthanum compounds--paramagnetic materials--intraatomic electron correlations--mott hubbard correlation gap--orbital ordering--paramagnetic phases--electronic structure
Аннотация: The electron structure of undoped LaMnO3 and slightly doped La1-xSrxMnO3 manganites has been calculated within the framework of a generalized tight binding method with explicit allowance for strong intra-atomic electron correlations. According to the results of these calculations, the ground state in orbitally disordered undoped LaMnO3 ferromagnets would be metallic despite the Mott-Hubbard correlation gap in the spectrum of quasiparticles. Owing to the orbital ordering, the insulating state is stabilized in both antiferromagnetic and paramagnetic phases. In-gap states of a polaron nature with a spectral weight proportional to the dopant concentration have been found near the top of the valence band in La1-xSrxMnO3. As the doping level increases, a metal state appears in the ferromagnetic phase, which has a metallic character for one spin subband and an insulating character for the other subband (representing the so-called half-metallic state).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Second moment of multiple-quantum NMR and a time-dependent growth of the number of multispin correlations in solids
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 103, Is. 6. - P904-916. - ISSN 1063-7761, DOI 10.1134/S1063776106120089
Примечания : Cited References: 39
Предметные рубрики: NUCLEAR-MAGNETIC-RESONANCE
LINE-SHAPE
SPIN SYSTEMS
DYNAMICS
SPECTRA
COHERENCES
STATE
BEHAVIOR
CRYSTAL
MODEL
Ключевые слова (''Своб.индексиров.''): correlation methods--mathematical models--nuclear magnetic resonance spectroscopy--spectrum analysis--time series analysis--four-spin time correlation--multispin correlations--second moment--time power series--quantum theory
Аннотация: The time evolution of multispin correlations (the growth of the number of correlated spins as a function of time) can be observed directly using the multiple-quantum nuclear magnetic resonance spectroscopy of solids. A quantity related to this number, namely, the second moment n(2)(t) of the intensity distribution of coherences of different orders in the multiple-quantum spectrum can be calculated using the theory proposed in this work. An approach to the calculation of the four-spin time correlation function through which this moment is expressed is developed. The main sequences of contributions in the expansion of this function into a time power series are summed using the approximation of a large number of neighbors both for systems with a secular dipole-dipole interaction and for systems with a nonsecular effective interaction. An exponential dependence of n(2)(t) is obtained. The value of n(2)(t) is additionally calculated using an expansion in terms of orthogonal operators for three model examples corresponding to different limiting realizations of spin systems. It is shown that the results of the microscopic theory at least qualitatively agree with both the results obtained for model examples and experimental results obtained recently for adamantane.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Felk V. A.
Заглавие : Effects of long-wave inhomogeneities of the exchange and elastic force constants in the framework of the coherent potential approximation
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2006. - Vol. 74, Is. 17. - Ст.174415. - ISSN 1098-0121, DOI 10.1103/PhysRevB.74.174415
Примечания : Cited References: 14
Предметные рубрики: CRYSTALS
MODEL
Аннотация: The formalism of averaged Green's functions in the continuum is developed for spin waves in ferromagnets with inhomogeneities of the exchange constant and elastic waves in media with inhomogeneities of the force constant. The integral self-consisted equation in the coherent potential approximation is developed for taking into account effects of inhomogeneities of these nonlocal characteristics of the material on the wave spectrum in it. The obtained general results are applied to the study of effects of one-dimensional inhomogeneities of the exchange constant on the wave spectrum in a ferromagnet.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Density of hole-doped states in strongly correlated electron-systems of copper oxides
Разночтения заглавия :авие SCOPUS: Density of hole-doped states in strongly correlated electron systems of copper oxides
Место публикации : Phys. Rev. B. - 1994. - Vol. 49, Is. 14. - P.9891-9897. - ISSN 0163-1829, DOI 10.1103/PhysRevB.49.9891
Примечания : Cited References: 34
Предметные рубрики: DYNAMIC PROPERTIES
SUPERCONDUCTIVITY
GAP
LA2CUO4
BI2SR2CACU2O8
PHOTOEMISSION
SPECTROSCOPY
SPECTRA
MODEL
BAND
Аннотация: A generalized tight-binding method to calculate quasiparticle band structure and density of states in strongly correlated systems is presented. The band structures of undoped and weakly hole-doped CuO2 layer are calculated. The insulator gap has a charge transfer nature with a minor contribution from a Cu-O Coulomb interaction. Doping results in the appearance of an in-gap state with a simultaneous decrease of the density of states at the band edges in agreement with small cluster results and experimental data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Deich L. I.
Заглавие : Far-infrared attenuation in glasses
Разночтения заглавия :авие SCOPUS: Far-infrared attenuation in glasses
Место публикации : Phys. Rev. B. - 1994. - Vol. 49, Is. 1. - P.109-113. - ISSN 0163-1829, DOI 10.1103/PhysRevB.49.109
Примечания : Cited References: 29
Предметные рубрики: VITREOUS SILICA
TEMPERATURE
MODEL
LOCALIZATION
ABSORPTION
SOLIDS
STATES
Аннотация: The influence of quasilocal vibrations on the far-infrared spectra of glasses is investigated under the supposition that the quasilocal vibrations are directly inactive in the attenuation. It is shown that taking into account phonon-quasilocal-vibration coupling and both medium- and short-range structure of the inhomogeneities of a photon-phonon coupling parameter can give rise to an attenuation curve similar to one observed for a-SiO2 and related materials.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : SANDALOV I. S., HJORTSTAM O., JOHANSSON B., ERIKSSON O.
Заглавие : ORBITAL POLARIZATION IN METALLIC F-ELECTRON SYSTEMS
Разночтения заглавия :авие SCOPUS: Orbital polarization in metallic f-electron systems
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 1995. - Vol. 51, Is. 20. - P13987-14000. - ISSN 0163-1829, DOI 10.1103/PhysRevB.51.13987
Примечания : Cited References: 28
Предметные рубрики: MOTT INSULATORS
VOLUME COLLAPSE
CERIUM
LOCALIZATION
TRANSITION
PHASES
MODEL
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Mitskan V. A., Petrakovskii G. A.
Заглавие : The magnetoelastic mechanism of singlet phase formation in a two-dimensional quantum antiferromagnet
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 2. - P234-247. - ISSN 1063-7761, DOI 10.1134/S106377610602004X
Примечания : Cited References: 18
Предметные рубрики: GROUND-STATE
SPIN
TRANSITION
CUGEO3
MODEL
Ключевые слова (''Своб.индексиров.''): crystal lattices--elasticity--mathematical models--oscillations--phase diagrams--phase transitions--quantum theory--two dimensional--atomic representation--magnetoelastic mechanism--quantum antiferromagnets--singlet phase formation--antiferromagnetic materials
Аннотация: A model describing the second-order phase transition with respect to the magnetoelastic coupling parameter from the anti ferromagnetic (AFM) to the singlet state in a two-dimensional quantum magnet on a square lattice is proposed. The spectrum of elementary excitations in the singlet and AFM phases is calculated using an atomic representation, and the evolution of transverse and longitudinal branches of this spectrum is studied in the vicinity of the transition point. It is established that the AFM to singlet phase transition is related to softening of the longitudinal branch of oscillations. In the singlet phase, the gap plays the role of a parameter characterizing the distance to the phase transition point. It is shown that the spectrum of transverse oscillations in the AFM phase corresponds to the Goldstone boson. Based on an analysis of the stability of the spectrum of elementary excitations, a phase diagram is constructed that determines the regions of the existence of phases with plaquette-deformed lattices.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : OVCHINNIKOV S.G.
Заглавие : THE INFLUENCE OF THE ANTIFERROMAGNETISM ON THE ELECTRONIC-STRUCTURE OF LA2CUO4
Разночтения заглавия :авие SCOPUS: The influence of the antiferromagnetism on the electronic structure of La2CuO4
Место публикации : J. Supercond.: PLENUM PUBL CORP, 1995. - Vol. 8: University-of-Miami Workshop on High-Temperature Superconductivity - Physical Properties and Mechanisms (JAN 05-11, 1995, CORAL GABLES, FL), Is. 5. - P675-676. - ISSN 0896-1107, DOI 10.1007/BF00727473
Примечания : Cited References: 15
Предметные рубрики: OXIDES
MODEL
Ключевые слова (''Своб.индексиров.''): electron correlations--electron structure--spin fluctuations--electron correlations--electron structure--spin fluctuations--antiferromagnetism--band structure--calculations--correlation theory--electrons--lanthanum compounds--paramagnetism--perturbation techniques--antiferromagnetic phase--electron correlations--intercluster interactions--spin fluctuations--electronic structure
Аннотация: The quasiparticle approach for electronic structure calculations considering strong electron correlations is given. The exact diagonalization of a multiband Hubbard Hamiltonian for a small cluster is combined with perturbation theory for intercluster hopping. The band structure of paramagnetic and antiferromagnetic La2CuO4 are discussed.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Erkaev N. V., Biernat H. K., Farrugia C. J.
Заглавие : Ideal magnetohydrodynamic flow around a blunt body under anisotropic pressure
Место публикации : Phys. Plasmas: AMER INST PHYSICS, 2000. - Vol. 7, Is. 8. - P3413-3420. - ISSN 1070-664X, DOI 10.1063/1.874205
Примечания : Cited References: 23
Предметные рубрики: MHD FLOW
MAGNETOSHEATH
DEPLETION
CLOSURE
FLUID
MODEL
Аннотация: The plasma flow past a blunt obstacle in an ideal magnetohydrodynamic (MHD) model is studied, taking into account the tensorial nature of the plasma pressure. Three different closure relations are explored and compared with one another. The first one is the adiabatic model proposed by Chew, Goldberger, and Low. The second closure is based on the mirror instability criterion, while the third depends on an empirical closure equation obtained from observations of solar wind flow past the Earth's magnetosphere. The latter is related with the criterion of the anisotropic ion cyclotron instability. In the presented model, the total pressure, defined as the sum of magnetic pressure and perpendicular plasma pressure, is assumed to be a known function of Cartesian coordinates. The calculation is based on the Newtonian approximation for the total pressure along the obstacle and on a quadratic behavior with distance from the obstacle along the normal direction. Profiles of magnetic field strength and plasma parameters are presented along the stagnation stream line between the shock and obstacle of an ideal plasma flow with anisotropy in thermal pressure and temperature. (C) 2000 American Institute of Physics. [S1070- 664X(00)04407-4].
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Role of zinc and nickel impurities in high-temperature superconductors
Место публикации : Phys. Solid State: AMER INST PHYSICS, 1999. - Vol. 41, Is. 4. - P534-538. - ISSN 1063-7834, DOI 10.1134/1.1130819
Примечания : Cited References: 32
Предметные рубрики: PR2-XCEXCUO4+DELTA SINGLE-CRYSTALS
SR-CU-O
COPPER OXIDES
MAGNETIC-PROPERTIES
NI
MODEL
ZN
SUBSTITUTION
SCATTERING
SPECTRUM
Аннотация: The local changes produced in the electronic structure and their effect on the physical properties of the superconducting and normal phases when zinc and nickel are substituted for copper are examined on the basis of a multiband p-d model. It is shown that strong electronic correlations suppress the S = 1 configuration of Ni2+ and cause the superposition of the S = 1/2 and S = 0 states of nickel. The change in the density of states in p- and n-type systems is studied, and the peculiarity of Zn impurity for p- type systems and Ni impurity for n-type systems is shown. The universal dependence of the T-c on the residual resistance in lightly doped superconductors and deviations from it in optimally doped systems are discussed. (C) 1999 American Institute of Physics. [S1063-7834(99)00704-2].
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Borisov A. A., Ovchinnikov S. G.
Заглавие : Polarized ARPES spectra of undoped cuprates
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2001. - Vol. 43, Is. 10. - P1876-1884. - ISSN 1063-7834, DOI 10.1134/1.1410625
Примечания : Cited References: 15
Предметные рубрики: ELECTRONIC-STRUCTURE
COPPER OXIDES
PHOTOEMISSION
EVOLUTION
MODEL
HOLE
Аннотация: The spectral density (SD) in the ARPES spectra of anti ferromagnetic (AFM) dielectrics Sr2CuO2Cl2 and Ca2CuO2Cl2 along the principal symmetry directions of the Brillouin zone was studied by the generalized tight binding method. At the valence band top of these undoped cuprates in the AFM state, there is a pseudogap of magnetic nature with E-s(k) similar to 0-0.4 eV between a virtual level and the valence band proper. The observed similarity of dispersion along the Gamma -M and X-Y directions can be explained by the proximity of the B-3(1g) triplet and the Zhang-Rice singlet levels. The value of parity of the polarized ARPES spectra at the Gamma, M, and X points calculated for the AFM phase of undoped cuprates with an allowance for the partial contributions is even. The conditions favoring observation of the partial contributions in polarized ARPES spectra are indicated. Due to the spin fluctuations, the virtual level acquires dispersion and possesses a small spectral weight. Probably, this level cannot be resolved on the background of the main quasi-particle peak as a result of the damping effects. (C) 2001 MAIK "Nauka/Interperiodica".
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : On the coordinate of a singular point of the time correlation function for a spin system on a simple hypercubic lattice at high temperatures
Место публикации : Theor. Math. Phys. - 2002. - Vol. 131, Is. 3. - P.862-872. - ISSN 0040-5779, DOI 10.1023/A:1015935809388
Примечания : Cited References: 19
Предметные рубрики: NUCLEAR-DOUBLE-RESONANCE
HEISENBERG MAGNET
DEPENDENCE
MODEL
Ключевые слова (''Своб.индексиров.''): spin dynamics--correlation functions--power series in time--frequency moments--singular points--generated functions--lattice trees--multidimensional expansion--correlation functions--frequency moments--generated functions--lattice trees--multidimensional expansion--power series in time--singular points--spin dynamics
Аннотация: Using the d(-1) expansion method (d is the space dimension), we estimate the coordinate of the time-dependent autocorrelation function singular point on the imaginary time axis for the spin 1/2 Heisenberg model on a simple hypercubic lattice at high temperatures. We represent the coefficients of the time expansion (the spectral moments) for the autocorrelation function as the sums of the weighted lattice figures in which the trees constructed from the double bonds give the leading contributions with respect to d(-1) and the same trees with the built-in squares from six bonds or diagrams with the fourfold bonds give the contribution of the next-to-leading order. We find the corrections to the coordinate of the autocorrelation function singular point that are due to the latter contributions.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Erkaev N. V., Semenov V. S., Alexeev I. V., Biernat H. K.
Заглавие : Rate of steady-state reconnection in an incompressible plasma
Место публикации : Phys. Plasmas: AMER INST PHYSICS, 2001. - Vol. 8, Is. 11. - P4800-4809. - ISSN 1070-664X, DOI 10.1063/1.1410112
Примечания : Cited References: 16
Предметные рубрики: MAGNETIC RECONNECTION
CURRENT SHEETS
MODEL
Аннотация: The reconnection rate is obtained for the simplest case of two-dimensional (2D) symmetric reconnection in an incompressible plasma. In the short note [Erkaev , Phys. Rev. Lett. 84, 1455 (2000)], the reconnection rate is found by matching the outer Petschek solution and the inner diffusion region solution. Here the details of the numerical simulation of the diffusion region are presented and the asymptotic procedure which is used for deriving the reconnection rate is described. The reconnection rate is obtained as a decreasing function of the diffusion region length. For a sufficiently large diffusion region scale, the reconnection rate becomes close to that obtained in the Sweet-Parker solution with the inverse square root dependence on the magnetic Reynolds number Re-m, determined for the global size of the current sheet. On the other hand, for a small diffusion region length scale, the reconnection rate turns out to be very similar to that obtained in the Petschek model with a logarithmic dependence on the magnetic Reynolds number Re-m. This means that the Petschek regime seems to be possible only in the case of a strongly localized conductivity corresponding to a small scale of the diffusion region. (C) 2001 American Institute of Physics.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : A study of anisotropic Heisenberg antiferromagnet with S=1/2 on a square lattice by Monte-Carlo method
Место публикации : Phys. Status Solidi B. - 1998. - Vol. 207, Is. 2. - P.491-498. - ISSN 0370-1972, DOI 10.1002/(SICI)1521-3951(199806)207:2491::AID-PSSB4913.0.CO;2-G
Примечания : Cited References: 24
Предметные рубрики: EU2CUO4
LA2CUO4
ORDER
MODEL
STATE
Аннотация: The two-dimensional (2D) Heisenberg model (J 0) with anisotropic exchange Delta = 1-J(X)/J(Z) greater than or equal to 0 and with S = 1/2 is studied by the quantum Monte-Carlo method. Energy, susceptibility, specific heat, spin-spin correlation functions, and correlation radius are calculated. The dependence of the Neel temperature T(N)/J = 2/ln(11/Delta) on the exchange anisotropy is determined. The static magnetic factor is very slowly decreased for T/J 0.4. It is assumed to realize topological excitations in the range of these temperatures. The correlation radius of the isotropic Heisenberg model is fitted by the dependence 1/xi = 2.05T(1.0(6))/exp (1.0(4)/T).The temperature behavior of the static structural magnetic factor in La(2)CuO(4) and Er(2)CuO(4) for T T(N) is in agreement with the MC calculations.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : On the radius of convergence of series in powers of time for spin correlation functions of the Heisenberg magnet at high temperature
Место публикации : Theor. Math. Phys.: PLENUM PUBL CORP, 1997. - Vol. 112, Is. 3. - P1182-1191. - ISSN 0040-5779, DOI 10.1007/BF02583049
Примечания : Cited References: 22
Предметные рубрики: AUTO-CORRELATION FUNCTION
INFINITE-TEMPERATURE
PARAMAGNET
DYNAMICS
MODEL
Аннотация: The convergence of series in powers of time for spin autocorrelation functions of the Heisenberg magnet are investigated at infinite temperatures on lattices of different dimensions d. The calculation data available at the present time for the coefficients of these series are used to estimate the corresponding radii of convergence, whose growth with decreasing d is revealed and explained in a self-consistent approximation. To this end, a simplified nonlinear equation corresponding to this approximation is suggested and solved for the autocorrelation function of a system with an arbitrary number Z of nearest neighbors. The coefficients of the expansion in powers of time for the solution are represented in the form of trees on the Bethe lattice with the coordination number Z. A computer simulation method is applied to calculate the expansion coefficients for trees embedded in square, triangular, and simple cubic lattices under the condition that the intersection of tree branches is forbidden. It is found that the excluded volume effect that manifests itself in a decrease in these coefficients and in an increase in the coordinate and exponent of the singularity of the autocorrelation function on the imaginary time axis is intensified with decreasing lattice dimensions.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Bondarenko I. N.
Заглавие : Magnetic ordering and phase transitions in planar antiferromagnetic systems with a Kagome lattice
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 1998. - Vol. 86, Is. 6. - P1209-1215. - ISSN 1063-7761, DOI 10.1134/1.558592
Примечания : Cited References: 23
Предметные рубрики: TRIANGULAR LATTICE
2 DIMENSIONS
SPIN
MODEL
Аннотация: We study the process of magnetic ordering in planar antiferromagnetic systems with a Kagome lattice. It is found that if the interaction between next-nearest-neighbor spins is taken into account, the heat capacity of such systems has a singularity at a finite temperature T. On the basis of a scaling analysis of finite-size systems we study the behavior of thermodynamic quantities in the neighborhood of a phase transition. We find that the phase transition at the critical point is due to discrete- and continuous-symmetry breaking, in which the long-range chiral order and the power-law translational spin order emerge simultaneously. Finally, we calculate the temperatures of the transition to different (with three and nine spins per unit cell) ordered states. (C) 1998 American Institute of Physics.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo analysis of the 2D Heisenberg antiferromagnet with S=1/2: the influence of exchange anisotropy
Разночтения заглавия :авие SCOPUS: Quantum Monte Carlo analysis of the 2D Heisenberg antiferromagnet with S = 1/2: The influence of exchange anisotropy
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 1998. - Vol. 10, Is. 44. - P10061-10065. - ISSN 0953-8984, DOI 10.1088/0953-8984/10/44/012
Примечания : Cited References: 21
Предметные рубрики: SQUARE LATTICE
SYSTEMS
MODEL
Аннотация: The two-dimensional (2D) Heisenberg model with exchange anisotropy Delta = 1 - J(x)/J(z) (J 0) and S
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sukhinin Y. V.
Заглавие : Phase transitions in self-assembled monolayers of alkanethiols containing the polar group
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 1998. - Vol. 87, Is. 1. - P115-122. - ISSN 1063-7761, DOI 10.1134/1.558645
Примечания : Cited References: 38
Предметные рубрики: ORGANIZED MOLECULAR ASSEMBLIES
ALKYL THIOL MONOLAYERS
STRUCTURAL CHARACTERIZATION
DYNAMICS SIMULATION
LANGMUIR MONOLAYER
SURFACES
GOLD
FILMS
AU(111)
MODEL
Аннотация: Equilibrium states of the system of self-assembled monolayers (SAMs) of n-alkanethiol molecules HS(CH2)(n-1)(X) with polar group X chemiabsorbed on the Au(111) crystal surface are considered. The couplings between the atoms (C, H) of the n-alkanethiols are approximated by the Lennard-Jones potential. The couplings between the n-alkanethiols and the crystal surface are approximated by the 12-3 potential. The interactions of polar groups and the self-images with the metal substrate are taken into consideration. The phase-transition temperatures, the structural order and equilibrium tilt, and the twist and azimuthal angles of the macromolecules, which depend on the dipole moments, are found. (C) 1998 American Institute of Physics.
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