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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S., Romanova O. B., Har'kov A. M., Balaev D. A., Gorev M. V., Vorotynov A. M., Sokolov V. V., Pichugin A.
Заглавие : Metal–semiconductor transition in SmxMn1−xS solid solutions
Место публикации : Phys. Status Solidi B. - 2012. - Vol. 249, Is. 4. - P.812-817. - ISSN 0370-1972, DOI 10.1002/pssb.201147327
Примечания : Cited References: 27. - This study was supported by the Russian Foundation for Basic Research project No 09-02-00554_a; No 09-02-92001-NNS_a; No 11-02-98018 r_sibir_a; ADTP "Development of scientific potential of the higher school" No. 2.1.1/11763.
Предметные рубрики: Magnetic-properties
Phase-transition
SmS
Valence
Pressure
Crystal
Lattice
CeRhSb
Ключевые слова (''Своб.индексиров.''): kondo effect--metal-semiconductor transition--semiconductors--variable-valence elements
Аннотация: The electrical resistivity of the SmxMn1−xS (0.15 ≤ x ≤ 0.25) solid solutions in the temperature range of 80–300 K was measured. Minimum and maximum in the temperature dependence of the resistivity were found, respectively, at T = 220 K for x = 0.15 and at T = 100 K for x = 0.2 compounds. This behavior is explained from the result of the mobility-edge movement, the disorder being due to elastic deformation and spin density fluctuations with short-range order. Metal–semiconductor phase transition versus concentration at xc = 0.25 is observed. Resistivity is described by scattering electrons with acoustic phonon mode and with localized manganese spin. From the thermal expansion coefficient the compression of the lattice below the Néel temperature for Sm0.2Mn0.8S is found.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kolovsky A. R., Link J., Wimberger S.
Заглавие : Energetically constrained co-tunneling of cold atoms
Место публикации : New J. Phys.: IOP Publishing Ltd, 2012. - Vol. 14. - Ст.75002. - ISSN 1367-2630, DOI 10.1088/1367-2630/14/7/075002
Примечания : Cited References: 18. - The present project was supported by the Excellence Initiative (Enable Fund of the Faculty of Physics and Astronomy, Heidelberg University). Moreover, SW acknowledges financial support from the DFG through FOR760, the Helmholtz Alliance Program of the Helmholtz Association (contract number HA-216: Extremes of density and temperature: cosmic matter in the laboratory), and by the Heidelberg Graduate School of Fundamental Physics (grant number GSC 129/1) and AK acknowledges support from the Russian Foundation for Basic Research (project number 12-02-000094-a: Tunneling of the macroscopic quantum states) and by the Siberian Branch of RAS (project no. 29: Dynamics of atomic Bose-Einstein condensates in optical lattices). AK is very grateful for the hospitality of the Institute of Theoretical Physics of Heidelberg University.
Предметные рубрики: LATTICE
Аннотация: We study under-barrier tunneling for a pair of energetically bound bosonic atoms in an optical lattice with a barrier. We identify the conditions under which this exotic molecule tunnels as a point particle with the coordinate given by the bound pair center of mass and discuss the atomic co-tunneling beyond this regime. In particular, we quantitatively analyze resonantly enhanced co-tunneling, where two interacting atoms penetrate the barrier with higher probability than a single atom.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Zlotnikov A. O.
Заглавие : On the implementation of the coexistence phase of antiferromagnetism and superconductivity in heavy-fermion intermetallides
Место публикации : JETP Letters. - 2012. - Vol. 95, Is. 7. - P.350-356. - ISSN 0021-3640, DOI 10.1134/S0021364012070089
Примечания : Cited References: 29. - This work was supported by the Presidium of the Russian Academy of Sciences (program "Quantum Mesoscopic and Disordered Structures"), the Russian Foundation for Basic Research (project nos. 10-02-00251 and 11-02-98007-Siberia), and the Ministry of Education and Science of the Russian Federation (federal program "Human Capital for Science and Education in Innovative Russia" for 2009-2013).
Предметные рубрики: QUANTUM-CRITICAL-POINT
CRITICAL PRESSURE
CERHIN5
LATTICE
Аннотация: The region of the state diagram in which the pressure-induced quantum phase transition occurs with the destruction of the antiferromagnetic ordering and the appearance of the superconductivity has been described within the periodic Anderson model. It has been shown that a microscopically homogeneous coexistence phase of antiferromagnetism and superconductivity is implemented in the vicinity of the critical point, which was experimentally found in the heavy-fermion compound CeRhIn5. In this region, the pressure increase is accompanied by the experimentally observed strong growth of the effective fermion mass.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Quantum and classical correlations in the solid-state NMR free induction decay
Место публикации : Appl. Magn. Reson.: Springer, 2014. - Vol. 45, Is. 11. - P.1169-1177. - ISSN 0937-9347, DOI 10.1007/s00723-014-0562-2. - ISSN 1613-7507
Примечания : Cited References: 16
Предметные рубрики: LATTICE
SPINS
Аннотация: The free induction decay (FID) of the transverse magnetization in a dipolar-coupled rigid lattice is a fundamental problem in magnetic resonance and in the theory of many-body systems. As it was shown earlier the FID shapes for the systems of classical magnetic moments and for quantum nuclear spin ones coincide if there are many nearly equivalent nearest neighbors n in a solid lattice. In this paper, we reduce a multispin density matrix of above system to a two-spin matrix. Then we obtain analytic expressions for the mutual information and the quantum and classical parts of correlations at the arbitrary spin quantum number S, in the high-temperature approximation. The time dependence of these functions is expressed via the derivative of the FID shape. To extract classical correlations for S 1/2 we provide generalized POVM measurement (positive-operator-valued measure) using the basis of spin coherent states. We show that in every pair of spins the portion of quantum correlations changes from 1/2 to 1/(S + 1) when S is growing up, and quantum properties disappear completely only if S → ∞.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : EFFECTIVE INTERACTIONS IN THE PERIODIC ANDERSON MODEL IN THE REGIME OF MIXED VALENCY WITH STRONG CORRELATIONS
Коллективы :
Разночтения заглавия :авие SCOPUS: Effective interactions in the periodic Anderson model in the regime of mixed valency with strong correlations
Место публикации : Theor. Math. Phys.: SPRINGER, 2008. - Vol. 157, Is. 2. - P1565-1576. - ISSN 0040-5779, DOI 10.1007/s11232-008-0130-8
Примечания : Cited References: 19. - This work was supported in part by the Russian Foundation for Basic Research (Grant No. 07-02-00226), a program of the Branch of Physical Sciences, Russian Academy of Sciences, and the "Integration Project" of the Siberian Branch, Russian Academy of Sciences.
Предметные рубрики: LATTICE
Ключевые слова (''Своб.индексиров.''): periodic anderson model--mixed valency--heavy fermion--effective hamiltonian--superconductivity--effective hamiltonian--heavy fermion--mixed valency--periodic anderson model--superconductivity
Аннотация: For the periodic Anderson model in the strong correlation regime, we construct the effective Hamiltonian H(eff) up to terms of the fourth order in the parameter V/U, where V is the hybridization interaction intensity and U is the intra-atom Coulomb repulsion strength. This Hamiltonian contains interactions inducing both magnetic ordering and Cooper instability under conditions of a mixed valency of rare-earth ions. Based on numerical calculations, we obtain information about the dependences of the effective interaction parameters on the distance between crystal lattice sites. We demonstrate that realizing exchange interactions corresponds to a strongly frustrated system of localized spin moments and facilitates the suppression of the antiferromagnetic order parameter with a possible transition to the state of a quantum spin liquid. It is essential that among the terms in H(eff) inducing the transition to the superconductivity phase, there are terms resulting in the d-type symmetry of the superconductivity order parameter; such a symmetry is realized in many heavy-fermion compounds.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : Spin-Fluctuation Renormalization of the Temperature of a Superconducting s-Phase in Rare-Earth Intermetallides
Коллективы :
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 107, Is. 4. - P679-691. - ISSN 1063-7761, DOI 10.1134/S1063776108100166
Примечания : Cited References: 34. - This study was supported in part by the Russian Foundation for Basic Research ( project no. 07-02-00226), the Department of Physic of the Russian Academy of Sciences ( within the program "Strongly Correlated Electrons in Semiconductors, Superconductors, and Magnetic Materials"), and the Siberian Branch of the Russian Academy of Sciences ( integration project no. 3.4).
Предметные рубрики: HEAVY-FERMION SUPERCONDUCTORS
PERIODIC ANDERSON MODEL
WAVE SUPERCONDUCTIVITY
PERTURBATION-THEORY
MECHANISM
VALENCE
SYSTEMS
LATTICE
STATE
Ключевые слова (''Своб.индексиров.''): differential equations--electric conductivity--green's function--numerical analysis--rare earth elements--spin dynamics--spin fluctuations--anomalous components--critical temperatures--experimental datums--infinite systems--numerical calculations--order parameters--periodic anderson models--renormalization--s-phase--skutterudite--strong electron correlations--sub systems--superconducting states--superconductivity
Аннотация: A theory of the superconducting state with s-type symmetry of the order parameter ( the transition to this state was observed in recently discovered heavy-fermion skutterudite LaFe(4)P(12)) is developed using the periodic Anderson model in the limit of strong electron correlations. Exact representations of Green's functions of the superconducting phase via the normal and anomalous components of the mass and strength operators are obtained. It is shown that an important role in the description of this superconducting phase is played by the anomalous components of the strength operator, which reflect spin-fluctuation processes in the localized subsystem. These components are calculated in the one-loop approximation using the solution of an infinite system of integral equations of self-consistency for the superconducting phase. Numerical calculations show that allowance for the process of scattering on spin fluctuations leads to renormalization of the critical temperature and provides agreement with the experimental data.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Martynov S. N., Balaev A. D.
Заглавие : Frustration mechanism of formation of a helical magnetic structure in the CuB2O4 two-subsystem antiferromagnet
Место публикации : JETP Letters. - 2007. - Vol. 85, Is. 12. - P.649-654. - ISSN 0021-3640, DOI 10.1134/S0021364007120132
Примечания : Cited References: 21
Предметные рубрики: PHASE 10 K
COPPER METABORATE
LATTICE
Аннотация: A new mechanism is proposed for forming an incommensurate magnetic structure of the transverse helix type owing to the removal of frustration through intersubsystem exchange in a two-subsystem antiferromagnet. The symmetry analysis of the distribution of the Dzyaloshinskii-Moriya interaction and comparison with the experimental data on the field dependence of magnetization indicate that antisymmetric exchange and competition between symmetric exchanges cannot be responsible for forming a helical magnetic structure in CuB2O4.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Bondarenko I. N.
Заглавие : A quantum spin liquid in a two-layer triangular antiferromagnet
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 101, Is. 5. - P868-880. - ISSN 1063-7761, DOI 10.1134/1.2149066
Примечания : Cited References: 43
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
DIMER GROUND-STATE
MEAN-FIELD THEORY
HEISENBERG-ANTIFERROMAGNET
SYSTEM SRCU2(BO3)(2)
PHASE-TRANSITION
GAP
FLUCTUATIONS
EXCITATIONS
LATTICE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--magnetic fields--magnetization--phase diagrams--spectrum analysis--thermodynamics--analogous systems--square lattices--thermodynamic quantities--two-layer triangular antiferromagnets--quantum theory
Аннотация: The possibility of implementing a quantum-spin-liquid-type state in a two-layer triangular spin-1/2 antiferromagnet at T = 0 is investigated. The ratio of intra- to interlayer exchange constants (j) is found under which a transition from the classical state with 120 degrees triangular order to a quantum state with zero magnetization per site occurs; in this case, the spins of adjacent layers form singlets that are separated from triplet excitations by an energy gap. Compared with an analogous system with the square lattice, the range of j in which the classical ordered state is realized turns out to be an order of magnitude smaller due to the effects of frustration; in this case, the behavior of thermodynamic quantities is analogous, on the whole, to that in two-layer square lattices; a difference manifests itself in the behavior of the gap in the spectrum of quasiparticles in an external magnetic field h. For small fields h, a j-h phase diagram is constructed that determines the domains in which the 120 degrees and the singlet phases exist. It is established that, in the neighborhood of the second-order phase transition, the contribution, to the thermodynamic quantities, of longitudinal spin fluctuations, which are disregarded in the spin-wave description, is comparable to the contribution of transverse fluctuations. (c) 2005 Pleiades Publishing, Inc.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min E. V., Ovchinnikov S. G., Singh D. J.
Заглавие : Effect of frustrations on magnetism in the Ru double perovskite Sr2YRuO6
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2003. - Vol. 68, Is. 2. - Ст.24409. - ISSN 1098-0121, DOI 10.1103/PhysRevB.68.024409
Примечания : Cited References: 24
Предметные рубрики: MOTT TRANSITION
LATTICE
SPIN
ANTIFERROMAGNETISM
SUPERCONDUCTIVITY
FERROMAGNETISM
Аннотация: Localized Ru5+ spins in Sr2YRuO6 form a fcc lattice with an antiferromagnetic (AFM) nearest-neighbor (NN) coupling J approximate to 25 meV and rather low Neel temperature T-N= 26 K. Analysis of the electronic structure of Sr2RuO4 results in the effective Heisenberg model. We have studied the effect of frustrations on the AFM type-I structure of Sr2YRuO6 in the spin-wave approximation. In the model with only NN coupling the AFM state is unstable due to frustrations, and T-N = 0. Stabilization of the AFM state occurs due to the next-nearest-neighbor coupling I or due to the magnetic anisotropy D. Very small values D/J similar to I/J less than or equal to 10(-3) are enough to obtain the experimental values of T-N and sublattice magnetization m = 1.85 mu(B) /Ru (62% from the nominal S = 3/2 value).
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Ovchinnikov S. G.
Заглавие : Generalization of Luttinger's theorem for strongly correlated electron systems
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2003. - Vol. 45, Is. 8. - P1415-1422. - ISSN 1063-7834, DOI 10.1134/1.1602872
Примечания : Cited References: 19. - The authors are grateful to V.V. Val’kov for helpful remarks. This work was supported by the INTAS (grant no. INTAS-01-0654), the Russian Foundation for Basic Research and the Krasnoyarsk KraÏ Science Foundation (program “EniseÏ,” project no. 02-02-97705), the program of the Russian Academy of Sciences “Quantum Macrophysics,” and the Russian Academy of Sciences, Siberian Division (Lavrent’yev Contest for Youth Projects)
Предметные рубрики: NARROW ENERGY BANDS
HUBBARD-MODEL
FERMI-SURFACE
LATTICE
Аннотация: By on the analyzing the general structure of the Green function of a strongly correlated electron system, it is shown that, for the regime of strong correlations, Luttinger's theorem should be generalized in the following way: the volume of the Fermi surface of the system of noninteracting particles is equal to that of the quasiparticles in the strongly correlated system with due regard for the spectral weight of the quasiparticles. An investigation of the t-J model and of the Hubbard model, as applied to the paramagnetic nonsuperconducting phase, shows that the generalized Luttinger theorem is valid for these models. (C) 2003 MAIK "Nauka/Interperiodica".
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