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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M. Y., Valkov V. V.
Заглавие : Anomalous resistivity and superconductivity in the two-band Hubbard model with one narrow band (Review)
Место публикации : Low Temp. Phys. - 2011. - Vol. 37, Is. 1. - P.69-82. - ISSN 1063-777X, DOI 10.1063/1.3552118; \b Физика низких температур
Примечания : Cited References: 62. - We thank A.S. Alexandrov, A.F. Andreev, M.A. Baranov, Yu. Bichkov, A.V. Chubukov, D.V. Efremov, A.S. Hewson, K.A. Kikoin, F.V. Kusmartsev, P. Nozieres, T.M. Rice, A.O. Sboychakov, P. Thalmeer, C.M. Varma, D. Vollhardt, P. Woelfle, A. Yaresko and, especially, P. Fulde, Yu. Kagan, K.I. Kugel, and N.V. Prokof'ev for many simulating discussions on this subject and acknowledge the financial support of RFBR grants # 08-02-00224 and 08-02-00212. M.Yu.K. is also grateful to the Leverhulme trust for a grant to visit Loughborough University, where this work was completed.
Предметные рубрики: FERMI-LIQUID BEHAVIOR
MAGNETIC-ALLOYS
HEAVY
DENSITY
SYSTEMS
STATE
UPT3
MECHANISM
PARTICLE
VALENCE
Аннотация: We search for marginal Fermi-liquid behavior in the two-band Hubbard model with one narrow band. We consider the limit of low electron densities in the bands and strong intraband and interband Hubbard interactions. We analyze the influence of electron-polaron effects and other mechanisms for mass-enhancement (related to the momentum dependence of the self-energies) on the effective mass and scattering times of light and heavy components in the clean case (electron-electron scattering and no impurities). We find a tendency towards phase separation (towards negative partial compressibility of heavy particles) in the 3D case with a large mismatch between the densities of heavy and light bands in the strong coupling limit. We also find that for low temperatures and equal densities, the resistivity in a homogeneous state R(T) proportional to T-2 behaves as a Fermi-liquid in both 3D and 2D. For temperatures greater than the effective bandwidth for heavy electrons T W-h*, the coherence of the heavy component breaks down completely. The heavy particles move diffusively in the surrounding light particles. At the same time, light particles scatter on heavy particles as if on immobile (static) impurities. Under these conditions, the heavy component is marginal, while the light component is not. The resistivity approaches saturation for T W-h* in the 3D case. In 2D the resistivity has a maximum and a localization tail owing to weak-localization corrections of the Altshuler-Aronov type. This behavior of resistivity in 3D could be relevant for some uranium-based heavy-fermion compounds such as UNi2Al3 and in 2D, for some other mixed-valence compounds, possibly including layered manganites. We also consider briefly the superconductive (SC) instability in this model. The leading instability tends to p-wave pairing and is governed by an enhanced Kohn-Luttinger mechanism for SC at low electron densities. The critical temperature corresponds to the pairing of heavy electrons via polarization of the light electrons in 2D. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552118]
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Valkov V. V., Dzebisashvili D. M.
Заглавие : Influence of antiferromagnetic ordering on the de Haas-van Alphen effect in a semimetal
Место публикации : Phys. Solid State: AMER INST PHYSICS, 1997. - Vol. 39, Is. 2. - P179-184. - ISSN 1063-7834, DOI 10.1134/1.1129779
Примечания : Cited References: 19
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
NORMAL STATE
OSCILLATIONS
CEAS
Аннотация: The distinctive characteristics of the de Haas-van Alphen effect in semimetals with antiferromagnetic long-range order are investigated theoretically. It is shown that the transition of the subsystem of localized spins from the canted antiferromagnetic phase to the ferromagnetic phase is accompanied by an abrupt change in the ''frequency'' of the magnetization oscillations of band carriers M-similar to. In the below-critical range of magnetic fields, M-similar to is not a function periodic in 1/H. Significantly, the additional contribution to the phase of the oscillatory factors is proportional to H-2 and is determined entirely by quantum fluctuations in the antiferromagnetic subsystem. (C) 1997 American Institute of Physics.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Furrer A., Fisher P., Roessli B., Petrakovskii G. A., Sablina K. A., Valkov V. V., Fedoseev B.
Заглавие : Investigation of spin-waves in single-crystal Bi2CuO4 by inelastic neutron-scattering
Место публикации : Solid State Commun. - 1992. - Vol. 82, Is. 6. - P.443-446. - ISSN 0038-1098, DOI 10.1016/0038-1098(92)90746-V
Примечания : Cited References: 9
Аннотация: Neutron scattering experiments have been employed to study the spin-wave excitations and the critical behaviour of sublattice magnetization of a single crystal Bi2CuO4. Dispersion law for spin waves along the tetragonal axis of crystal is determined. There were found two branches of spin waves which are characterized by the energy gaps DELTA-1 congruent-to 1.7 meV and DELTA-2 congruent-to 4.0 meV, respectively. The value of critical exponent beta = 0.36 + 0.08 reflects the 3D character of the magnetic ordering in Bi2CuO4. Observed two spin-wave branches are described on the basis of the anisotropic tetragonal spin-Hamiltonian with four-sites exchange interaction.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : VALKOV V. V.
Заглавие : UNITARY TRANSFORMATIONS OF THE GROUP U(N) AND DIAGONALIZATION OF MULTILEVEL HAMILTONIANS
Место публикации : Theor. Math. Phys.: PLENUM PUBL CORP, 1988. - Vol. 76, Is. 1. - P766-772. - ISSN 0040-5779, DOI 10.1007/BF01029435
Примечания : Cited References: 20
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Valkov V. V., Valkova T. A., Ovchinnikov S. G.
Заглавие : Spectrum of excitations of an easy-plane ferromagnet (s = 3/2) in a magnetic-field
Место публикации : Phys. Status Solidi B. - 1987. - Vol. 142, Is. 1. - P.255-263. - ISSN 0370-1972, DOI 10.1002/pssb.2221420126
Примечания : Cited References: 22
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : VALKOV V. V., VALKOVA T. A.
Заглавие : INFLUENCE OF CUBIC ANISOTROPY ON THE GROUND-STATE AND THERMODYNAMIC PROPERTIES OF HEISENBERG MAGNETS
Место публикации : Theor. Math. Phys.: PLENUM PUBL CORP, 1984. - Vol. 59, Is. 3. - P617-625. - ISSN 0040-5779, DOI 10.1007/BF01018202
Примечания : Cited References: 18
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : VALKOV V. V., OVCHINNIKOV S. G.
Заглавие : HUBBARD OPERATORS AND SPIN-WAVE THEORY OF HEISENBERG MAGNETS WITH ARBITRARY SPIN
Место публикации : Theor. Math. Phys.: PLENUM PUBL CORP, 1982. - Vol. 50, Is. 3. - P306-313. - ISSN 0040-5779, DOI 10.1007/BF01016463
Примечания : Cited References: 32
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Valkov V. V., Ovchinnikov S. G.
Заглавие : Mixed-valence phase-transition in ferromagnets
Место публикации : Phys. Status Solidi B. - 1981. - Vol. 108, Is. 2. - P.601-608. - ISSN 0370-1972, DOI 10.1002/pssb.2221080238
Примечания : Cited References: 13
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : VALKOV V. V., KHRUSTALEV B. P.
Заглавие : MAGNETIZATION OF GRANULATED HTSC IN INTENSE MAGNETIC-FIELDS
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1995. - Vol. 107, Is. 4. - P1221-1231. - ISSN 0044-4510
Примечания : Cited References: 18
Предметные рубрики: CRITICAL-STATE MODEL
HIGH-TEMPERATURE SUPERCONDUCTORS
HIGH-TC SUPERCONDUCTORS
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Valkov V. V., Valkova T. A.
Заглавие : Application of indefinite metric for transition to bose description of Su(3) hamiltonians - excitation spectrum of spin nematics
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz. - 1991. - Vol. 99, Is. 6. - P.1881-1897. - ISSN 0044-4510
Примечания : Cited References: 37
Предметные рубрики: BIQUADRATIC EXCHANGE
PHASE-TRANSITIONS
DIAGRAM TECHNIQUE
MAGNETISM
FIELD
STATE
Аннотация: A procedure is developed for a correct transition to the Bose representation for quantum SU(3) Hamiltonians. The analysis is carried out for a spin nematic by applying the indefinite metric formalism and pseudo-Hubbard operators. An important aspect of the theory is that the finiteness of the number of physical states is taken into account. This is attained by introducing and consistently taking into account the metric operator for which purpose a simple expression in terms of Bose operators is suggested. It is shown that in this approach the quantum Bose analog of the Hamiltonian is an Hermitian operator. This circumstance removes a number of principle contradictions which appeared previously on application of the Bose analog of the Hamiltonian derived by virtually identifying the Hubbard and pseudo-Hubbard operators and ignoring the finiteness of the number of physical states. The integral equations defining the chief characteristics of the system are obtained and solved analytically for the spin-nematic state of a magnet with S = 1 and by taking into account anharmonic effects. This permits one to write down in nonlinear theory explicit expressions for the two branches of the quantum excitation spectrum. The character of the renormalization of the spectrum parameters due to the presence of zero-point quantum oscillations is studied. The renormalization of the critical field on transition of the system from the spin nematic state is calculated analytically.
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