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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M. Y., Val'kov V. V., Mitskan V. A., Korovushkin M. M.
Заглавие : The Kohn-Luttinger effect and anomalous pairing in new superconducting systems and graphene
Коллективы : Physics Department of the Russian Academy of Sciences [P.3.1]; Russian Foundation for Basic Research [14-02-00058, 14-02-31237]; Russian Federation [MK-526.2013.2]; Dynasty Foundation
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 118, Is. 6. - P.995-1011. - ISSN 1063-7761, DOI 10.1134/S1063776114060132. - ISSN 1090-6509
Примечания : Cited References: 114. - This study was supported by the Program of the Physics Department of the Russian Academy of Sciences (project no. P.3.1) and the Russian Foundation for Basic Research (project nos. 14-02-00058 and 14-02-31237). The work of two coauthors (M. M. K. and V.A.M) was supported financially by grant no. MK-526.2013.2 of the President of the Russian Federation and the Dynasty Foundation.
Предметные рубрики: P-WAVE SUPERCONDUCTIVITY
EXTENDED HUBBARD-MODEL
NARROW ENERGY-BANDS
2D KONDO-LATTICE
FERMI GAS
REPULSIVE INTERACTIONS
ELECTRON CORRELATIONS
COOPER INSTABILITY
PHASE-DIAGRAM
SPECTRUM
Аннотация: We present a review of theoretical investigations into the Kohn-Luttinger nonphonon superconductivity mechanism in various 3D and 2D repulsive electron systems described by the Fermi-gas, Hubbard, and Shubin-Vonsovsky models. Phase diagrams of the superconducting state are considered, including regions of anomalous s-, p-, and d-wave pairing. The possibility of a strong increase in the superconducting transition temperature T c even for a low electron density is demonstrated by analyzing the spin-polarized case or the two-band situation. The Kohn-Luttinger theory explains or predicts superconductivity in various materials such as heterostructures and semimetals, superlattices and dichalcogenides, high-T c superconductors and heavy-fermion systems, layered organic superconductors, and ultracold Fermi gases in magnetic traps. This theory also describes the anomalous electron transport and peculiar polaron effects in the normal state of these systems. The theory can be useful for explaining the origin of superconductivity and orbital currents (chiral anomaly) in systems with the Dirac spectrum of electrons, including superfluid 3He-A, doped graphene, and topological superconductors.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S., Vtyurin A. N., Shmygol' I. V., Goryainov S. V.
Заглавие : Phase transition in the layered perovskite CsScF4 induced by hydrostatic pressure
Место публикации : Phys. Solid State: American Institute of Physics, 1999. - Vol. 41, Is. 9. - P.1541-1543. - ISSN 1063-7834, DOI 10.1134/1.1131019
Примечания : Cited References: 9
Предметные рубрики: SPECTRUM
Аннотация: Using polarization microscopy and Raman scattering, we have discovered a new phase transition in the layered perovskite crystal CsScF4 under a hydrostatic pressure around 6 GPa. The proposed space group of the high-pressure phase is C-2h(2), Z=4. (C) 1999 American Institute of Physics. [S1063-7834(99)03109-3].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G.
Заглавие : Temperature dependence of the electronic structure of La2CuO4 in the multielectron LDA+GTB approach
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2015. - Vol. 121, Is. 3. - P.457-464. - ISSN 1063-7761, DOI 10.1134/S1063776115090174
Примечания : Cited References: 38. - The work was supported by the Russian Science Foundation (project no. 14-12-00061)
Предметные рубрики: Copper oxides
Model
Superconductivity
Excitations
Instability
Spectrum
States
Order
Аннотация: The band structure of La2CuO4 in antiferromagnetic and paramagnetic phases is calculated at finite temperatures by the multielectron LDA+GTB method. The temperature dependence of the band spectrum and the spectral weight of Hubbard fermions is caused by a change in the occupation numbers of local multielectron spin-split terms in the antiferromagnetic phase. A decrease in the magnetization of the sublattice with temperature gives rise to new bands near the bottom of the conduction band and the top of the valence band. It is shown that the band gap decreases with increasing temperature, but La2CuO4 remains an insulator in the paramagnetic phase as well. These results are consistent with measurements of the red shift of the absorption edge in La2CuO4 with increasing temperature. © 2015, Pleiades Publishing, Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorelik V. S., Pyatyshev A. Y., Krylov A. S.
Заглавие : Raman scattering in sodium nitrite crystals near the phase transition
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2016. - Vol. 58, Is. 1. - P.170-176. - ISSN 10637834 (ISSN), DOI 10.1134/S1063783416010133
Примечания : Cited References: 39. - This study was supported by the Russian Foundation for Basic Research (project nos. 12-02-00491, 13-02-00449, 13-02-90420, and 14-02-00190).
Предметные рубрики: NaNO2
SPECTROSCOPY
DEPENDENCE
SPECTRUM
SEARCH
MODES
Аннотация: Optical Raman spectra of a ferroelectric sodium nitrite crystal have been detected in a wide spectrum range at various temperatures, including the region of the ferroelectric phase transition. A manifestation of a transverse soft polar mode of the A1(z) type responsible for the ferroelectric phase transition has been discovered in the spectrum at room temperature. This mode has been found to become overdamped even far from the ferroelectric phase transition temperature. This mode also appears as a central peak under heating. It has been found that the pseudoscalar mode of the A2 type has the highest intensity in the Raman spectrum of sodium nitrite. The frequency corresponding to the maximum intensity of this mode in the Raman spectrum varies from 130 cm–1 at 123 K to 106 cm–1 at T = 513 K. A fair agreement of the experimental data for the A1(z) mode with the Lyddane–Sachs–Teller relation has been established. The polariton curves for the A1(z) polar mode and the dispersion curves for axinons has been plotted. © 2016, Pleiades Publishing, Ltd.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Iskhakov R. S., Stolyar S. V., Chizhik M. V., Chekanova L. A.
Заглавие : Spin-Wave Resonance in Multilayer Films (One-Dimensional Magnon Crystals). Identification Rules
Место публикации : JETP Letters. - 2011. - Vol. 94, Is. 4. - P.301-305. - ISSN 0021-3640, DOI 10.1134/S0021364011160077
Примечания : Cited References: 17. - This work was supported by the Ministry of Education and Science of the Russian Federation, project no. RNP 2.1.1/3498, program "Development of Scientific Potential of Higher Schools" for 2009 and 2010 and the program "Scientific and Pedagogical Personnel of Innovative Russia" for 2009-2013. We are grateful to Prof. V. A. Ignatchenko for stimulating discussions.
Предметные рубрики: SPECTRUM
ALLOYS
Аннотация: The characteristic modification of the spectrum of the exchange spin waves has been revealed in ferromagnet/ferromagnet multilayer films with a thickness of N(d(1) + d(2)) by the spin-wave resonance method. This modification is due to the first bandgap at the wavenumber k(b) = pi/(d(1) + d(2)) of a magnon crystal, which is formed by one-dimensional modulation of the magnetization. It has been shown that the transformation of the multilayer film with thermal annealing to the film of a single-phase alloy is accompanied by the disappearance of this modification of the spectrum. DOI: 10.1134/S0021364011160077
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pisarev R. V., Kalashnikova A. M., Schops O., Bezmaternykh L. N.
Заглавие : Electronic transitions and genuine crystal-field parameters in copper metaborate CuB2O4
Разночтения заглавия :авие SCOPUS: Electronic transitions and genuine crystal-field parameters in copper metaborate CuB 2O 4
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2011. - Vol. 84, Is. 7. - Ст.75160. - ISSN 1098-0121, DOI 10.1103/PhysRevB.84.075160
Примечания : Cited References: 65. - Useful discussions with W. Weber on crystal-field splitting of 3d states in cuprates are appreciated. We thank H.-J. Weber for the help in using Cary 2300 spectrophotometer. This work is supported by the Russian Foundation for Basic Research (project No. 09-02-00070) and Federal Agency for Science and Innovations (Grant No. 02.740.11.0384). A. M. K. acknowledges the financial support from the Committee for Science and Higher Education of the Government of Saint Petersburg.
Предметные рубрики: OPTICAL-ABSORPTION
PHASE-DIAGRAM
CUGEO3
SPECTRUM
SUPERCONDUCTORS
EXCITATIONS
SR2CUO2CL2
SCATTERING
LA2CUO4
CUPRATE
Аннотация: We present and analyze high-resolution alpha-, sigma-, and pi-polarized absorption spectra related to d-d electronic transitions in tetragonal metaborate CuB2O4 where copper Cu2+ ions occupy two crystallographically distinct 4b and 8d positions. The spectra are characterized by exceptionally rich fine structure in the spectral range of 1.4-2.4 eV. Six zero-phonon (ZP) lines originating from the electronic transitions within the Cu2+ ions in both positions are distinguished and identified. Symmetry analysis explains polarization properties of the ZP lines in the 8d positions but only partially explains them in the 4b positions. Reliable assignment of all six ZP lines to specific transitions allowed us to calculate genuine cubic Dq and tetragonal Ds and Dt crystal-field parameters for both positions. We show that the (3r(2) - z(2)) state, the energy of which is the measure of the Jahn-Teller splitting, is the highest 3d state for both types of Cu2+ ion positions. Using the obtained crystal-field parameters as the reference values, we estimated Dq, Ds, and Dt for several other cuprates with different Cu-O bond lengths. In particular, the 3d level splitting in La2CuO4, Nd2CuO4, CuGeO3, Sr2CuO2Cl2, and Cu3B7O13Cl was analyzed. Our estimates suggest that the Jahn-Teller splitting in some of these cuprates is larger than it was assumed previously.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G.
Заглавие : Effect of Interlayer Single-Particle Hoppings on the Superconducting Transition Temperature
Разночтения заглавия :авие SCOPUS: Effect of interlayer single-particle hoppings on the superconducting transition temperature
Место публикации : JETP Letters. - 2011. - Vol. 93, Is. 6. - P.339-343. - ISSN 0021-3640, DOI 10.1134/S0021364011060063
Примечания : Cited References: 27. - This work was supported by the Presidium of the Russian Academy of Sciences (program no. 18.7 "Quantum Physics of Condensed Matter"), by the Siberian and Ural Branches of the Russian Academy of Sciences (joint project no. 40), by the Russian Foundation for Basic Research (project no. 09-02-00127), by the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (project no. MK-1683.2010.2), and by the Ministry of Education and Science of the Russian Federation (project no. GK P891, federal program "Scientific and Pedagogical Personnel of Innovative Russia").
Предметные рубрики: T-J MODEL
DEPENDENCE
YBA2CU3O7-DELTA
ELECTRON
SPECTRUM
STRESS
Аннотация: It is well known that the superconducting transition temperature of high-T-c cuprates depends on the number of CuO2 planes in the unit cell. The multilayer structure implies the possibility of interlayer hopping. Under the assumption that the interlayer hopping can be specified by the parameter t(perpendicular to)(k) = t(perpendicular to)(cos(k(x)) - cos(k(y)))(2), the quasiparticle excitation spectrum for the bilayer cuprate in the superconducting state has been determined in the framework of the t - t' - t '' - t(perpendicular to) - J* model using the generalized mean-field approximation. It turns out that the interlayer hoppings does not create any additional mechanism of the Cooper paring and does not lead to an increase in T-c. The splitting of the upper Hubbard quasiparticle band attributed to the interlayer hoppings is manifested as two peaks in the doping dependence of the superconducting transition temperature at temperatures below the maximum T-c value for a single-layer cuprate. It has been found that antiferromagnetic interlayer correlations suppress the interlayer splitting. This probably leads to the common doping dependence of T-c for both single-layer and bilayer cuprates.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Makarov I. A., Shneyder E. I.
Заглавие : Effect of interlayer tunneling on the electronic structure of bilayer cuprates and quantum phase transitions in carrier concentration and high magnetic field
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 112, Is. 2. - P288-302. - ISSN 1063-7761, DOI 10.1134/S106377611005119X
Примечания : Cited References: 64. - This study was supported financially by the program "Quantum Physics of Condensed Media" of the Presidium of the Russian Academy of Sciences (project no. 5.7), the integration projects of the Siberian Branch and the Ural Division of the Russian Academy of Sciences (project no. 40), the Russian Foundation for Basic Research (project no. 09-02-00127), the President of the Russian Federation (grant no. MK-1683.2010.2), and the Federal Target Program P891.
Предметные рубрики: T-J MODEL
HIGH-TEMPERATURE SUPERCONDUCTORS
DIMENSIONAL HUBBARD-MODEL
FERMI-SURFACE
COPPER OXIDES
GROUND-STATE
CUO2 PLANES
SPECTRUM
BAND
NMR
Ключевые слова (''Своб.индексиров.''): antibonding--bi-layer--bilayer cuprates--complex sequences--cuprates--doping levels--external magnetic field--field magnitude--hartree-fock approximations--high magnetic fields--lifshitz transition--main effect--orbitals--perturbation theory--quantum phase transitions--quantum transitions--single-layer structure--theoretical study--unit cells--carrier concentration--copper compounds--density functional theory--electronic properties--electronic structure--hartree approximation--magnetic fields--perturbation techniques--phase transitions--surface structure--quantum theory
Аннотация: We present a theoretical study of the electronic structure of bilayer HTSC cuprates and its evolution under doping and in a high magnetic field. Analysis is based on the t-t'-taEuro(3)-J* model in the generalized Hartree-Fock approximation. Possibility of tunneling between CuO2 layers is taken into account in the form of a nonzero integral of hopping between the orbitals of adjacent planes and is included in the scheme of the cluster form of perturbation theory. The main effect of the coupling between two CuO2 layers in a unit cell is the bilayer splitting manifested in the presence of antibonding and bonding bands formed by a combination of identical bands of the layers themselves. A change in the doping level induces reconstruction of the band structure and the Fermi surface, which gives rise to a number of quantum phase transitions. A high external magnetic field leads to a fundamentally different form of electronic structure. Quantum phase transitions in the field are observed not only under doping, but also upon a variation of the field magnitude. Because of tunneling between the layers, quantum transitions are also split; as a result, a more complex sequence of the Lifshitz transitions than in single-layer structures is observed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Sidorov K. A., Shneyder E. I.
Заглавие : Anomalous thermodynamics of the doped Mott-Hubbard insulators
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 2. - P299-302. - ISSN 1063-7834, DOI 10.1134/S1063783411020247
Примечания : Cited References: 6. - This study was supported by the Russian Foundation for Basic Research (project no. 09-02-00127), the Branch of the Physical Sciences of the Russian Academy of Sciences (program nos. 2 and 3), grant no. MK-1683.2010.2, and by the Federal Target Program "Personnel" (project NK-589 P).
Предметные рубрики: T-J MODEL
SPECTRUM
Аннотация: The concentration dependence of the entropy of doped Mott-Hubbard insulators has been considered within the t-J model. It has been shown that a change in the type and statistics of charge carriers as compared to the Fermi gas leads to a radical change in the entropy s, in particular, to the giant growth of the entropy upon doping. The quantity a,s/a,x a parts per thousand k (B) is approximately consistent with the experimental data for HTSC cuprates in the pseudogap phase.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mankov Y. I., Tsikalov D. S.
Заглавие : High-frequency susceptibility of a multilayered ferromagnetic system with two-dimensional inhomogeneities
Коллективы :
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 52, Is. 3. - P544-553. - ISSN 1063-7834, DOI 10.1134/S1063783410030157
Примечания : Cited References: 24. - This study was supported in part by the Council on Grants from the President of the Russian Federation for the State Support of Scientific Investigations performed by the Leading Scientific Schools (grant no. 3818.2008.3), the Presidium of the Russian Academy of Sciences (Program no. 27.1), and the Ministry of Education and Science within the framework of the Federal Program (State Contract no. 2.740.11.0220).
Предметные рубрики: SPIN-WAVE SUSCEPTIBILITY
SPECTRUM
SUPERLATTICES
INTERFACES
Аннотация: This paper reports on the results of the investigation of the high-frequency susceptibility of a layered ferromagnetic structure in which, apart from a periodic change in the magnetic anisotropy parameter from layer to layer, this parameter varies along layers according to a random law (the superlattice with two-dimensional phase inhomogeneities). The evolution of the frequency dependence of the imaginary part of the averaged Green's function in the range of the energy gap (band gap) in the spectrum of waves propagating along the superlattice axis due to the change in the relative root-mean-square fluctuations of the phase gamma 2 has been studied at the boundaries of the odd Brillouin zones. It has been found that, for all odd Brillouin zones, the imaginary part of the Green's function exhibits a universal behavior: the peak corresponding to the edge of the band gap with a lower frequency remains unchanged, and the peak corresponding to the edge of the band gap with a higher frequency is smoothed with an increase in the quantity gamma(2). These effects, which were initially revealed at the boundary of the first Brillouin zone of the sinusoidal superlattice, have been explained, as before, by the specific features of the energy conservation laws for the incident and scattered waves in the lattice with two-dimensional inhomogeneities. It has been demonstrated that an increase in the Brillouin zone number leads to a decrease in the value of gamma(2) at which the peak at the edge of the band gap with a higher frequency disappears.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Golovnya A. A.
Заглавие : Effect of Spin Fluctuations on the Superconducting Phase of Hubbard Fermions in the t-t'-t"-J* Model
Коллективы :
Разночтения заглавия :авие SCOPUS: Effect of spin fluctuations on the superconducting phase of Hubbard fermions in the t-t′-t″-J*model
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 107, Is. 6. - P996-1008. - ISSN 1063-7761, DOI 10.1134/S1063776108120091
Примечания : Cited References: 33. - This work was supported by the Program "Quantum Macrophysics" of the Presidium of the Russian Academy of Sciences, Russian Foundation for Basic Research (project no. 06.02.16100), and Integration project no. 3.4 of the Siberian Branch of the Russian Academy of Sciences.
Предметные рубрики: SPECTRUM
Ключевые слова (''Своб.индексиров.''): electric conductivity--fermions--integral equations--spin dynamics--spin fluctuations--anomalous components--critical temperatures--electron concentrations--hubbard--hubbard operators--joint effects--large systems--nonhomogeneous equations--one-loop approximations--order parameters--renormalization--scattering process--self energies--spin-fluctuation--strongly correlated electrons--superconducting phase--system of integral equations--superconductivity
Аннотация: The effect of spin-fluctuation scattering processes on the region of the superconducting phase in strongly correlated electrons (Hubbard fermions) is investigated by the diagram technique for Hubbard operators. Modified Gor'kov equations in the form of an infinitely large system of integral equations are derived taking into account contributions of anomalous components P(0 sigma),((sigma) over bar0) of strength operator P. It is shown that spin-fluctuation scattering processes in the one-loop approximation for the t-t'-t"-J* model taking into account long-range hoppings and three-center interactions are reflected by normal (P(0 sigma), (0 sigma)) and anomalous (P(0 sigma), ((sigma) over bar0)) components of the strength operator. Three-center interactions result in different renormalizations of the kernels of the integral equations for the superconducting d phase in the expressions for the self-energy and strength operators. In this approximation for the d-type symmetry of the order parameter for the superconducting phase, the system of integral equations is reduced to a system of nonhomogeneous equations for amplitudes. The resultant dependences of critical temperature on the electron concentrations show that joint effect of long-range hoppings, three-center interactions, and spin-fluctuation processes leads to strong renormalization of the superconducting phase region.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I., Tsikalov D. S.
Заглавие : High-Frequency Susceptibility of a Superlattice with 2D Inhomogeneities
Коллективы :
Разночтения заглавия :авие SCOPUS: High-frequency susceptibility of a superlattice with 2D inhomogeneities
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 107, Is. 4. - P603-611. - ISSN 1063-7761, DOI 10.1134/S1063776108100075
Примечания : Cited References: 26. - This work was supported in part by grant no. 3818.2008.3 from the President of Russia in accordance with the program supporting leading scientific schools.
Предметные рубрики: SPIN-WAVE SUSCEPTIBILITY
PERIODIC MULTILAYERS
LOCALIZATION
SYSTEMS
SPECTRUM
DISORDER
MEDIA
Ключевые слова (''Своб.индексиров.''): energy conservation--energy gap--energy management--frequency bands--gallium alloys--green's function--probability density function--three dimensional--band gaps--energy conservation laws--green functions--high frequencies--imaginary parts--magnon crystals--scattered waves--superlattice layers--wave spectrums--phase interfaces
Аннотация: We investigate the high-frequency susceptibility (Green function) of an initially sinusoidal 1D superlattice with 2D phase inhomogeneities that model the deformations of the interfaces between the superlattice layers. For waves propagating along the superlattice axis ( the geometry of a photon or magnon crystal), we have found a peculiar behavior of the imaginary part of the Green function that consists in a significant difference between the peaks corresponding to the edges of the band gap in the wave spectrum. The peak corresponding to the lower-frequency band edge remains essentially unchanged as the root-mean-square fluctuation of the 2D inhomogeneities. 2 increases, while the peak corresponding to the higher-frequency band edge broaden and decreases sharply in height until its complete disappearance with increasing gamma(2). This behavior of the peaks corresponds to a band gap closure mechanism that differs from the traditional one characteristic of 1D and 3D inhomogeneities. These effects can be explained by a peculiarity of the energy conservation laws for the incident and scattered waves for 2D inhomogeneities in a 1D superlattice.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Influence of two-particle excited states on the interatomic exchange interaction in La(2)CuO(4)
Разночтения заглавия :авие SCOPUS: Influence of two-particle excited states on the interatomic exchange interaction in La2CuO4
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 50, Is. 6. - P1081-1086. - ISSN 1063-7834, DOI 10.1134/S1063783408060140
Примечания : Cited References: 12. - This study was supported by the Integration Project of the Siberian Branch–Ural Branch of the Russian Academy of Sciences (project. no. 74), the Russian Academy of Sciences, the Presidium of the Russian Academy of Sciences within the program “Quantum Macrophysics,” and the Russian Foundation for Basic Research (project nos. 06-02-90537-BNTS and 07-02-00226)
Предметные рубрики: T-J MODEL
COPPER OXIDES
ELECTRON
SPECTRUM
Аннотация: The effective spin Hamiltonian for undoped cuprates is constructed in the framework of the realistic multiband p-d model with the parameters calculated from first principles. The exchange interaction parameter is defined as the sum of the antiferromagnetic and ferromagnetic contributions, which are determined by the two-hole triplet terms. The ferromagnetic and antiferromagnetic contributions of the excited terms compensate each other to a large extent. It is shown that the antiferromagnetic contribution of the two-hole ground singlet (1)A(1g) to the exchange interaction is dominant.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Laletin O. N.
Заглавие : Waves in a superlattice with arbitrary interlayer boundary thickness
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 12. - P2292-2300. - ISSN 1063-7834, DOI 10.1134/1.1841396
Примечания : Cited References: 34
Предметные рубрики: PERIODIC STRUCTURES
RAYLEIGH-WAVES
LAYERED MEDIUM
ELASTIC-WAVES
SPIN-WAVES
SPECTRUM
MEDIA
PROPAGATION
EXCITATIONS
MULTILAYERS
Аннотация: The transmittance D(omega), reflectance R(omega), and dispersion omega(k) are investigated for waves of various nature propagating through a one-dimensional superlattice (multilayer structure) with arbitrary thickness of the interlayer boundary. The dependences of the band gap widths Deltaomega(m) and their positions in the wave spectrum of the superlattice on the interlayer boundary thickness d and the band number m are calculated. Calculations are performed in terms of the modified coupled-mode theory (MCMT) using the frequency dependence of R(omega), as well as in the framework of perturbation theory using the function omega(k), which made it possible to estimate the accuracy of the MCMT method; the MCMT method is found to have a high accuracy in calculating the band gap widths and a much lower accuracy in determining the gap positions. It is shown that the m dependence of Deltaomega(m) for electromagnetic (or elastic) waves is different from that for spin waves. Furthermore, the widths of the band gaps with m = 1 and 2 are practically independent of d, whereas the widths of all gaps for m 2 depend strongly on d. Experimental measurements of these dependences allow one to determine the superlattice interface thicknesses by using spectral methods. (C) 2004 MAIK "Nauka/Interperiodica".
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : The coordinate of the singular point of generating functions of clusters in the high-temperature dynamics of spin lattice systems with axially symmetric interaction
Место публикации : Theor. Math. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2003. - Vol. 136, Is. 3. - P1297-1311. - ISSN 0040-5779, DOI 10.1023/A:1025603416535
Примечания : Cited References: 25
Предметные рубрики: CONSISTENT FLUCTUATING FIELD
NUCLEAR-DOUBLE-RESONANCE
HEISENBERG PARAMAGNET
LINE SHAPE
RELAXATION
SPECTRUM
APPROXIMATION
CRYSTALS
MOMENT
CAF2
Ключевые слова (''Своб.индексиров.''): spin dynamics--singular points--expansion over the reciprocal space dimension--expansion over the reciprocal space dimension--singular points--spin dynamics
Аннотация: We investigate generating functions for equipped trees composed of double bonds of two sorts on a hypercubic lattice of dimension d with built-in fragments. Rules for constructing these clusters are chosen to ensure the estimate for coefficients of power series in time for the longitudinal and transverse autocorrelation functions of the spin system with axially symmetric interaction. We derive a system of two equations for the tree-generating functions and an equation for the generating functions of chains leading from the root to a fragment in a tree using the Bethe approximation and under the condition that mainly bonds of one sort are taken into account. For the face-centered hypercubic lattice, we find the First terms of the 1/d expansion for the coordinate of the singular point of the generating function in both the anisotropic and the isotropic cases taking fragments in the forms of a triangle from four bonds and a four-fold bound pair into account. The obtained result is written in terms of ratios of lattice sums and is generalized to nuclear spin systems with dipole-dipole interaction. The theoretical value of the singular-point coordinate agrees well with the experimental value calculated from the tail of the absorption spectrum of the nuclear magnetic resonance in a barium fluoride monocrystal.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Maradudin A. A., Poszdnyakov A. V.
Заглавие : Waves in a superlattice with anisotropic inhomogeneities
Место публикации : JETP Letters. - 2003. - Vol. 78, Is. 9. - P.592-596. - ISSN 0021-3640, DOI 10.1134/1.1641491
Примечания : Cited References: 28
Предметные рубрики: PERIODIC MULTILAYERS
SPIN-WAVES
SPECTRUM
LOCALIZATION
SYSTEMS
MEDIA
DISORDER
AVERAGE
Аннотация: Dependences of the dispersion laws and damping of waves in an initially sinusoidal superlattice on inhomogeneities with anisotropic correlation properties are studied for the first time. The period of the superlattice is modulated by the random function described by the anisotropic correlation function K-phi(r) that has different correlation radii, k(parallel toparallel to)(-1) and k(perpendicular to)(-1), along the axis of the superlattice z and in the plane xy, respectively. The anisotropy of the correlation is characterized by the parameter lambda = 1 - k(perpendicular to)/k(parallel toparallel to) that can change from lambda = 0 to lambda = 1 when the correlation wave number k(perpendicular to) changes from k(perpendicular to) = k(parallel toparallel to) (isotropic 3D inhomogeneities) to k(perpendicular to) = 0 (1D inhomogeneities). The correlation function of the superlattice K(r) is developed. Its decreasing part goes to the asymptote L that divides the correlation volume into two parts, characterized by finite and infinite correlation radii. The dependences of the width of the gap in the spectrum at the boundary of the Brillouin zone Deltanu and the damping of waves xi on the value of lambda are studied. It is shown that decreasing L leads to the decrease of Deltanu, and increase of xi, with the increase of lambda. (C) 2003 MAIK "Nauka / Interperiodica".
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G.
Заглавие : The effective Hamiltonian of the singlet-triplet model for copper oxides
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2001. - Vol. 43, Is. 3. - P416-419. - ISSN 1063-7834, DOI 10.1134/1.1356113
Примечания : Cited References: 15
Предметные рубрики: HIGH-TC SUPERCONDUCTORS
BAND-STRUCTURE
LA2-XSRXCUO4
MECHANISM
SYMMETRY
SPECTRUM
Аннотация: The effective Hamiltonian for a realistic multiband p-d model is developed. In the case of electron doping, the Hamiltonian coincides with that for the standard t-J model. For hole doping, the singlet-triplet t-J model takes place. (C) 2001 MAIK "Nauka/Interperiodica".
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min E. V., Ovchinnikov S. G., Baklanov I. O., Goryachev E. G.
Заглавие : Microscopic model of the coexistence of superconductivity and ferromagnetism in the hybrid ruthenate-cuprate oxide RuSr2GdCu2O8
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2000. - Vol. 91, Is. 2. - P353-360. - ISSN 1063-7761, DOI 10.1134/1.1311995
Примечания : Cited References: 37
Предметные рубрики: T-J MODEL
HUBBARD-MODEL
LAYERED PEROVSKITE
SR2RUO4
ELECTRONS
COPPER
SPECTRUM
Аннотация: A microscopic t-J-I model with competing antiferromagnetic (J) and ferromagnetic (I) exchange interactions is proposed for strongly correlated electrons in RuSr2GdCu2O8 . It is assumed that J much greater than I for CuO2 layers and J much less than I for RuO2 layers. A superconducting solution of d(x2-y2) symmetry was obtained for the CuO2 layers while competition between ferromagnetism and p-type triplet superconducting pairing is obtained for RuO2 layers. It is shown that the RuO2 layers have a lower carrier concentration in the Hubbard subband formed by coupled ((d(xy)-p)-pi) orbitals compared with a bulk Sr2RuO4 crystal, which leads to stabilization of the ferromagnetic state in the RuO2 layer. (C) 2000 MAIK "Nauka/Interperiodica".
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G., Borisov A. A., Goryachev E. G.
Заглавие : Evolution of the band structure of quasiparticles with doping in copper oxides on the basis of a generalized tight-binding method
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2000. - Vol. 91, Is. 2. - P369-383. - ISSN 1063-7761, DOI 10.1134/1.1311997
Примечания : Cited References: 45
Предметные рубрики: T-J MODEL
CUPRATE SUPERCONDUCTORS
ELECTRONIC-STRUCTURE
EXCITATIONS
DEPENDENCE
TEMPERATURE
DERIVATION
SR2CUO2CL2
SPECTRUM
DENSITY
Аннотация: Two methods for stabilizing the two-hole B-3(1g) state as the ground state instead of the Zhang-Rice singlet are determined on the basis of an orthogonal cellular basis for a realistic multiband pd model of a CuO2 layer and the dispersion relations for the valence band top in undoped and doped cases are calculated. In the undoped case, aside from the valence band, qualitatively corresponding to the experimental ARPES data for Sr2CuO2Cl2 and the results obtained on the basis of the t-t'-J model, the calculations give a zero-dispersion virtual level at the valence band top itself. Because of the zero amplitude of transitions forming the virtual level the response corresponding to it is absent in the spectral density function. In consequence, the experimental ARPES data do not reproduce its presence in this antiferromagnetic undoped dielectric. A calculation of the doped case showed that the virtual level transforms into an impurity-type band and acquires dispersion on account of the nonzero occupation number of the two-hole states and therefore should be detected in ARPES experiments as a high-energy peak in the spectral density. The computed dispersion dependence for the valence band top is identical to the dispersion obtained by the Monte Carlo method, and the ARPES data for optimally doped Bi2Sr2CaCu2O8 + delta samples. The data obtained also make it possible to explain the presence of an energy pseudogap at the symmetric X point of the Brillouin band of HTSC compounds. (C) 2000 MAIK "Nauka/Interperiodica".
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Man'kov Y. I., Pozdnyakov A. V.
Заглавие : Spin-wave susceptibility of partially randomized ferromagnetic superlattices
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 1999. - Vol. 89, Is. 4. - P717-722. - ISSN 1063-7761, DOI 10.1134/1.559033
Примечания : Cited References: 15
Предметные рубрики: SPECTRUM
LOCALIZATION
Аннотация: This paper is a theoretical investigation of the effect of inhomogeneities in the period of a ferromagnetic superlattice on the high-frequency superlattice susceptibility. The calculations are done for a model in which the uniaxial magnetic anisotropy is taken as the physical parameter that characterizes both the ideal superlattice and a partially randomized superlattice. It is found that as the inhomogeneities become more intense, the two resonance peaks corresponding to the splitting of the spectrum at the edge of the Brillouin zone of the superlattice broaden, move closer to each other, and finally merge into one. The height of this peak increases and the peak width decreases as the intensity of the inhomogeneities increases further. The effect of inhomogeneities on the susceptibility differs dramatically in the two limits of short- and long-wave inhomogeneities: in the latter case (in contrast to the former) the dependence of the separation of the susceptibility peaks on the intensity and correlation properties of the inhomogeneities is nonmonotonic. The possibility of observing these effects in spin-wave resonance experiments involving multilayer magnetic films is also discussed. (C) 1999 American Institute of Physics. [S1063-7761(99)01510-3].
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