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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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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Petrakovskii G. A., Volkov N. V.
Заглавие : Antiferromagnetic resonance in CuB2O4 single crystal
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2000. - Vol. 42, Is. 1. - P96-102. - ISSN 1063-7834, DOI 10.1134/1.1131174
Примечания : Cited References: 20
Предметные рубрики: STATE
Аннотация: The frequency-field, temperature, and angular dependences of the antiferromagnetic resonance parameters for the tetragonal CuB2O4 single crystal are studied in the frequency range 2.6-80 GHz and at temperatures of 4.2-30 K. The results obtained confirm the fact that, in the high-temperature state in the range 10-21 K, this compound is an easy-plane weak ferromagnet. The temperature dependence of the Dzyaloshinski field is determined. An abrupt change observed in the frequency-field dependence of the magnetic resonance at T = 4.2 K and H perpendicular to C-4 indicates the transition to the weak ferromagnetic state induced by the external field H-perpendicular to. The phase diagram for CuB2O4 is constructed on the H-perpendicular to-T coordinates. It is demonstrated that, in the low-temperature state, the magnetic moments of copper ions remain in the basal plane, but the weak ferromagnetism is absent. (C) 2000 MAIK "Nauka/Interperiodica".
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Polukeev S. I., Ovchinnikov S. G.
Заглавие : Cation spin and superexchange interaction in oxide materials below and above spin crossover under high pressure
Коллективы : Russian Science FoundationRussian Science Foundation (RSF) [18-12-00022]
Место публикации : Phys. Rev. B. - 2020. - Vol. 101, Is. 9. - Ст.094409. - ISSN 2469-9950, DOI 10.1103/PhysRevB.101.094409. - ISSN 2469-9969(eISSN)
Примечания : Cited References: 65. - We acknowledge the support of the Russian Science Foundation through Grant No. 18-12-00022
Предметные рубрики: EXCHANGE INTERACTION
PHASE-TRANSITIONS
STATE
ELECTRON
IRON
Аннотация: We derived simple rules for the sign of 180° superexchange interaction based on the multielectron calculations of the superexchange interaction in the transition metal oxides that are valid both below and above spin crossover under high pressure. The superexchange interaction between two cations in dn configurations is given by a sum of partial contributions related to the electron-hole virtual excitations to the different states of the dn+1 and dn−1 configurations. Using these rules, we have analyzed the sign of the 180° superexchange interaction of a number of oxides with magnetic cations in electron configurations from d2 until d8: the iron, cobalt, chromium, nickel, copper, and manganese oxides with increasing pressure. The most interesting result concerns the magnetic state of cobalt and nickel oxides CoO, Ni2O3 and also La2CoO4, LaNiO3 isostructural to well-known high-TC and colossal magnetoresistance materials. These oxides have a spin 12 at the high pressure. Change of the interaction from antiferromagnetic below spin crossover to ferromagnetic above spin crossover is predicted for oxide materials with cations in d5(FeBO3) and d7(CoO) configurations, while for materials with the other dn configurations spin crossover under high pressure does not change the sign of the 180∘ superexchange interaction.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Nikolaev S. V., Ovchinnikov S. G.
Заглавие : Cluster perturbation theory in Hubbard model exactly taking into account the short-range magnetic order in 2 x 2 cluster
Коллективы :
Разночтения заглавия :авие SCOPUS: Cluster perturbation theory in Hubbard model exactly taking into account the short-range magnetic order in 2 × 2 cluster
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 111, Is. 4. - P635-644. - ISSN 1063-7761, DOI 10.1134/S1063776110100146
Примечания : Cited References: 23. - The authors thank V. V. Val'kov for fruitful discussions of this work. This research was supported financially by the Russian Foundation for Basic Research (project nos. 09-02-90723-mob_st and 09-02-00127) and by program no. 5.7 of the Presidium of the Russian Academy of Sciences and integration project no. 40 of the Siberian Branch and Ural Division of the Russian Academy of Sciences.
Предметные рубрики: INFINITE DIMENSIONS
SYSTEMS
STATE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic orders--characteristic energy--cluster perturbation theories--coulomb repulsions--density of state--dynamic mean field theories--eigenvalue problem--exact diagonalization--excited levels--finite temperatures--half-filling--hubbard--metal insulator transition temperature--nearest neighbors--numerical solution--pseudo-gap--quasiparticle spectrum--shadow zone--short-range magnetic orders--temperature evolution--zero temperatures--antiferromagnetism--eigenvalues and eigenfunctions--fermi level--hubbard model--mean field theory--metal insulator boundaries--perturbation techniques--semiconductor insulator boundaries--statistical mechanics--metal insulator transition
Аннотация: The cluster perturbation theory is presented in the 2D Hubbard model constructed using X operators in the Hubbard-I approximation. The short-range magnetic order is taken into account by dividing the entire lattice into individual 2 x 2 clusters and solving the eigenvalue problem in an individual cluster using exact diagonalization taking into account all excited levels. The case of half-filling taking into account jumps between nearest neighbors is considered. As a result of numerical solution, a shadow zone is discovered in the quasiparticle spectrum. It is also found that a gap in the density of states in the quasiparticle spectrum at zero temperature exists for indefinitely small values of Coulomb repulsion parameter U and increases with this parameter. It is found that the presence of this gap in the spectrum is due to the formation of a short-range antiferromagnetic order. An analysis of the temperature evolution of the density of states shows that the metal-insulator transition occurs continuously. The existence of two characteristic energy scales at finite temperatures is demonstrated, the larger scale is associated with the formation of a pseudogap in the vicinity of the Fermi level, and the smaller scale is associated with the metal-insulator transition temperature. A peak in the density of states at the Fermi level, which is predicted in the dynamic mean field theory in the vicinity of the metal-insulator transition, is not observed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krinitsyn A., Nikolaev S., Ovchinnikov S. G.
Заглавие : Cluster size and shape effect on the electronic structure of the Hubbard model within the norm-conserving cluster perturbation theory
Коллективы : Siberian Federal University [F-11]; Presidium of RAS Program [20.7]; [NSh-1044.2012.2]; [MK-1168.2012.2]
Место публикации : J. Supercond. Nov. Magn.: Springer, 2014. - Vol. 27, Is. 4. - P.955-963. - ISSN 1557-1939, DOI 10.1007/s10948-013-2418-7. - ISSN 1557-1947
Примечания : Cited References: 59. - This work was supported by Grants NSh-1044.2012.2 and MK-1168.2012.2, Siberian Federal University: Grant F-11, and the Presidium of RAS Program 20.7.
Предметные рубрики: NARROW ENERGY-BANDS
CUPRATE SUPERCONDUCTORS
PHOTOEMISSION SPECTRA
PSEUDOGAP
ANTIFERROMAGNET
EXCITATIONS
EVOLUTION
SYSTEMS
PHASE
STATE
Ключевые слова (''Своб.индексиров.''): cluster perturbation theory--hubbard model--strong correlations--density of states--fermi surface
Аннотация: Within a new norm-conserving approach to the cluster perturbation theory (CPT) for the 2d Hubbard model we study the effect of the cluster size and shape on the electronic structure. We have compared two type of clusters, 4-cluster (2x2) and 5-cluster (cruciform of 5 atoms). With 4-cluster we can treat exactly the first and second neighbours correlations, C (1) and C (2). With 5-cluster the third neighbour correlations C (3) are also treated exactly. The band structure in the CPT with 4- and 5-clusters differs remarkably. The quasiparticle spectral weight map for 5-clusters is very similar to the Quantum Monte Carlo (QMC) and the variational CPT data. With increasing doping, small hole Fermi surface transforms into conventional Fermi-liquid type large Fermi surface through Lifshitz quantum phase transitions.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kolovsky A. R.
Заглавие : Condition of correspondence between quantum and classical dynamics for a chaotic system
Место публикации : Phys. Rev. Lett.: AMER PHYSICAL SOC, 1996. - Vol. 76, Is. 3. - P340-343. - ISSN 0031-9007, DOI 10.1103/PhysRevLett.76.340
Примечания : Cited References: 18
Предметные рубрики: STANDARD MAP
STATE
Аннотация: The paper deals with the dynamics of a semiclassical system under the influence of the environment. The effect of the environment is shown to convert the quantum dynamics of the system into the classical one. The condition of correspondence between quantum and classical dynamics is obtained and checked numerically.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shneyder E. I., Ovchinnikov S. G., Shnurenko A. V.
Заглавие : Contribution of the non-Heisenberg ring exchange to the magnetic mechanism of high-Tc superconductivity
Место публикации : JETP Letters. - 2012. - Vol. 95, Is. 4. - P.193-197. - ISSN 0021-3640, DOI 10.1134/S0021364012040078
Примечания : Cited References: 44. - This work was supported by the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (project no. NSh-1044.2012.2), by the Russian Foundation for Basic Research (project no. 12-02-00040), by the Presidium of the Russian Academy of Sciences (program no. 20 "Quantum Mesoscopic and Disordered Systems"), jointly by the Siberian and Ural Branches of the Russian Academy of Sciences, by Siberian Federal University (project no. s/b S-11), and by the Ministry of Education and Science of the Russian Federation (state contract no. P891, federal program "Human Capital"). E.I.Sh. acknowledges the support of the Dynasty Foundation.
Предметные рубрики: BAND HUBBARD-MODEL
COPPER OXIDES
ELEMENTARY EXCITATIONS
SPIN
ELECTRON
STATE
T/U
Аннотация: The effect of non-Heisenberg four-spin ring exchange on the superconducting transition temperature in strongly correlated electron systems is studied. It is shown that the ring exchange can significantly suppress the contribution of the Heisenberg exchange to superconducting pairing.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ma, Bin, Guo Q. F., Molokeev M. S., Lv, Zhenfei, Yao, Jun, Mei, Lefu, Huang, Zhaohui
Заглавие : Crystal structure and luminescence properties of green-emitting Sr1−xAl12O19:xEu2+ phosphors
Место публикации : Ceram. Int.: Elsevier Science, 2016. - Vol. 42, Is. 5. - P.5995-5999. - ISSN 0272-8842, DOI 10.1016/j.ceramint.2015.12.149. - ISSN 1873-3956(eISSN)
Примечания : Cited References: 30. - This work was supported by the National Natural Science Foundation of China (Grant nos. 51032007 and 51372232) and the Fundamental Research Funds for the Central Universities (Grant no. 2652015024).
Предметные рубрики: COLOR-TUNABLE PHOSPHOR
ENERGY-TRANSFER
Dy3+ PHOSPHORS
NEAR-UV
Eu2+
DIODES
PHASE
STATE
Ce3+
Ключевые слова (''Своб.индексиров.''): crystal structure--magnetoplumbite--phosphor
Аннотация: In this paper, a series of novel luminescent Sr1−xAl12O19:xEu2+ phosphors were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the decay curves were investigated. The quenching concentration of Eu2+ in SrAl12O19 was about 0.15 (mol). Upon excitation at 378 nm, the composition-optimized Sr0.85Al12O19:0.15Eu2+ exhibited strong broad-band green emission at 530 nm with the CIE chromaticity (0.2917, 0.5736). The results indicate that Sr1−xAl12O19:xEu2+ phosphors have potential applications as green-emitting phosphors for UV-pumped white-light LEDs.
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