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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M., Barabanov A. F.
Заглавие : Basis states and collective excitations of nonlocal three-spin polarons over the singlet phase of the CuO2 plane
Место публикации : JETP Letters. - 2012. - Vol. 95, Is. 4. - P.206-212. - ISSN 0021-3640, DOI 10.1134/S0021364012040091
Примечания : Cited References: 15. - This work was supported by the Presidium of the Russian Academy of Sciences (program "Quantum Physics of Mesoscopic and Disordered Systems"), the Russian Foundation for Basic Research (project nos. 10-02-00251 and 11-02-98007-r-sibir'), 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: HEISENBERG-ANTIFERROMAGNET
SQUARE LATTICE
SPIN-POLARON
MODEL
Аннотация: An orthonormalized basis describing the single-hole states of the CuO2 plane has been constructed exactly taking into account the p-d exchange coupling between the spins of a hole and the two nearest copper ions. The introduced basis makes it possible to include the effects caused by the dependence of the Heisenberg interaction between the nearest copper ions on the occupation of the intermediate oxygen ion by the hole in the calculation of the spectrum of the collective excitations of nonlocal three-spin polarons. The inclusion of this correlation, as well as the nonlocality of the p-d exchange coupling, is the main difference of the developed approach to the description of the energy structure from the calculations with the use of the Zhang-Rice singlet.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Val'kova T. A., Shklyaev A. A.
Заглавие : Quantum fluctuations in a two-dimensional antiferromagnet with four-spin interaction of cubic symmetry
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 10. - P2061-2066. - ISSN 1063-7834, DOI 10.1134/S1063783411100350
Примечания : Cited References: 13. - This study was supported by the Presidium of the Russian Academy of Sciences (Program "Quantum Physics of Condensed Matter"), the Siberian Branch of the Russian Academy of Sciences (Interdisciplinary Integration project no. 53), the Ministry of Education and Science of the Russian Federation (Russian Federal Targeted Program "Scientific and Scientific-Pedagogical Personnel of the Innovative Russia" in 2009-2013), and the Russian Foundation for Basic Research (project no. 09-02-00127).
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
TEMPERATURE
STATE
Аннотация: The excitation spectrum of a non-Heisenberg 2D antiferromagnet with the four-spin interaction of cubic symmetry has been calculated in the first order of 1/2S. It has been shown that, for weak anisotropy, the N,el state is destroyed by quantum fluctuations. The phase diagrams showing the stability regions of the N,el phase in the space of spin-anisotropy parameters have been plotted.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Shneyder E. I., Korshunov M. M.
Заглавие : From underdoped to overdoped cuprates: two quantum phase transitions
Разночтения заглавия :авие SCOPUS: From underdoped to overdoped cuprates: Two quantum phase transitions
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2011. - Vol. 23, Is. 4. - Ст.45701. - ISSN 0953-8984, DOI 10.1088/0953-8984/23/4/045701
Примечания : Cited References: 58. - We would like to thank S Sakai for useful discussions. The authors acknowledge support by the Russian Foundation for Basic Research (grant N 09-02-00127), by the Integration Program of SBRAS N40, the Presidium RAS Program 5.7, President of Russia (grant MK-1683.2010.2), FCP Scientific and Research-and-Educational Personnel of Innovative Russia for 2009-2013 (GK P891), and in part by the National Science Foundation under grant NSF PHY05-51164.
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
T-J MODEL
CORRELATED FERMION SYSTEMS
VALENCE BOND STATE
MEAN-FIELD-THEORY
CRITICAL-POINT
HEISENBERG-ANTIFERROMAGNET
EXCITATIONS
PSEUDOGAP
OSCILLATIONS
Ключевые слова (''Своб.индексиров.''): critical concentration--critical points--cuprates--density of state--fermi surface topology--hall effect measurement--high-t--optimal doping--overdoped--pseudo-gap--quantum phase transitions--theoretical study--copper compounds--hall effect--magnetic field effects--phase diagrams--phase transitions
Аннотация: Several experimental and theoretical studies indicate the existence of a critical point separating the underdoped and overdoped regions of the high-T-c cuprates' phase diagram. There are at least two distinct proposals on the critical concentration and its physical origin. The first one is associated with the pseudogap formation for p p*, with p* approximate to 0.2. The other relies on the Hall effect measurements and suggests that the critical point and the quantum phase transition (QPT) take place at optimal doping, p(opt) approximate to 0.16. Here we have performed a precise density of states calculation and found that there are two QPTs and the corresponding critical concentrations associated with the change of the Fermi surface topology upon doping.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S., Moskvin A. I.
Заглавие : Magnetic structures upon ordering of e(g) orbitals in a square lattice
Разночтения заглавия :авие SCOPUS: Magnetic structures upon ordering of eg orbitals in a square lattice
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2008. - Vol. 20, Is. 32. - Ст.325202. - ISSN 0953-8984, DOI 10.1088/0953-8984/20/32/325202
Примечания : Cited References: 11
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
S=1/2
PHASE
Ключевые слова (''Своб.индексиров.''): crystallography--exchange mechanisms--magnetic structure
Аннотация: The exchange mechanism effect on the ordering of electrons on e(g) orbitals in a two-dimensional Heisenberg model with exchange anisotropy for a S = 1/2 spin is determined. The regions of existence of long-range quasi-one- and two-dimensional antiferromagnetic order with the special exchange topology are calculated by a quantum Monte Carlo method. The Neel temperature and quantum reduction of spin on site for an antiferromagnet with the stripe structure is estimated as a function of exchange anisotropy.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min E. V.
Заглавие : Quantum spin liquid in the FCC lattice
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2003. - Vol. 96, Is. 1. - P129-139. - ISSN 1063-7761, DOI 10.1134/1.1545392
Примечания : Cited References: 12
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
TRANSITION
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--green's function--linear systems--magnetic couplings--quantum theory--thermodynamic properties--antiferromagnetic interactions--green temperature functions--heisenberg model--quantum spin liquid--spin system--spin-wave theory--crystal lattices
Аннотация: The properties of the spin system in the FCC lattice described by the Heisenberg model (s=1/2) with antiferromagnetic interactions between the nearest neighbors were studied. It was shown within the framework of spin-wave theory that long-range antiferromagnetic order was absent because of frustration of exchange coupling and transverse quantum spin fluctuations. The system was in the quantum spin liquid state. A method for describing it within linear second-order theory with self-consistently calculated parameters was suggested. It was proved that the ground spin liquid state was singlet. The thermodynamic properties of the spin liquid in the whole temperature range and the character of spatial spin correlations, which had alternating signs and a finite correlation length, were determined. The theory was constructed based on the method of two-time Green temperature functions. (C) 2003 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bondarenko I. N., Gekht R. S., Ponomarev V. I.
Заглавие : Magnetic transitions in layered triangular antiferromagnets
Место публикации : Phys. Lett. A: ELSEVIER SCIENCE BV, 1996. - Vol. 222, Is. 4. - P269-274. - ISSN 0375-9601, DOI 10.1016/0375-9601(96)00635-4
Примечания : Cited References: 22
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
PHASE-TRANSITION
VBR2
SYSTEMS
FIELD
VCL2
Ключевые слова (''Своб.индексиров.''): triangular antiferromagnets--quantum and thermal fluctuations--successive phase transitions--quantum and thermal fluctuations--successive phase transitions--triangular antiferromagnets
Аннотация: Magnetic states and phase transitions of the layered triangular antiferromagnets in an applied field are studied. It is shown that in compounds like VBr2 and VCl2 quantum effects change the ground state structure and cause successive phase transitions as the magnetic field increases. Coplanar structures of different spin configuration are realized far from the saturation field and a noncoplanar structure of umbrella-type configuration is realized near this field. The ground-state phase diagram is constructed, and a finite region of fields where the collinear phase is also possible is indicated.
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