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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kadomtseva A. M., Popov Y. F., Vorob'ev G. P., Kostyuchenko N. V., Popov A. I., Mukhin A. A., Ivanov V. Y., Bezmaternykh L. N., Gudim, I. A., Temerov V. L., Pyatakov A. P., Zvezdin A. K.
Заглавие : High-temperature magnetoelectricity of terbium aluminum borate: The role of excited states of the rare-earth ion
Коллективы : Russian Foundation for Basic Research [13-02-12443, 13-02-01093, 12-02-01261, 13-02-12442]; Russian Federation President on support of sciences schools [4828.2012.2]; Ministry of Education and Science of Russian Federation [8365]
Место публикации : Phys. Rev. B: American Physical Society, 2014. - Vol. 89, Is. 1. - Ст.014418. - ISSN 1098-0121, DOI 10.1103/PhysRevB.89.014418. - ISSN 1550-235X
Примечания : Cited References: 25. - We thank Dr. Daniel Sando for useful comments and remarks. This work is supported by the Russian Foundation for Basic Research (Projects No. 13-02-01093, No. 13-02-12443, No. 13-02-01093, No. 12-02-01261, and No. 13-02-12442) and a grant from the Russian Federation President on support of sciences schools no. 4828.2012.2, The Ministry of Education and Science of Russian Federation, Project No. 8365.
Предметные рубрики: GROUND-STATE
PRFE3(BO3)4
MULTIFERROICS
Аннотация: Recently discovered magnetoelectricity in the rare-earth aluminum borates RAl3(BO3)4 has attracted attention due to the large values of magnetoinduced electric polarization. We have observed for the first time the magnetoelectric polarization in TbAl3(BO3)4 exhibiting anomalous temperature dependence: an electric polarization induced by in-plane magnetic field (P||a,H⊥c axis) which is small at low temperatures (4K), remarkably increases by almost an order of magnitude at high temperatures (150–300K). The observed nonmonotonic temperature behavior of the field-induced polarization, including a change of sign at ∼65–70K, is attributed to the competition of the ground and excited crystal-field states of Tb3+ ions. Quantum theory analysis, involving the combination of analytical and numerical methods, has enabled us to quantitatively describe the observed magnetic and magnetoelectric properties of TbAl3(BO3)4.Недавно обнаруженное магнетоэлектричество в редкоземельных алюмоборатах RAl3 (BO3) 4 привлекло к себе внимание из-за больших значений магнитоиндуцированной электрической поляризации. Мы наблюдали в первый раз магнитоэлектрическую поляризацию в TbAl3 (BO3) 4, показывающую аномальную температурную зависимость: электрическая поляризация индуцируется в плоскости магнитного поля (Р | |, Н ⊥ оси с), и является небольшой при низких температурах (4K), Значительно увеличивается, почти на порядок величины, при высоких температурах (150-300 К). Наблюдаемая с изменением температуры немонотонность поляризации от поля, в том числе изменению знака на ~ 65-70 К, может быть отнесена к конкуренции между основном и возбужденном кристаллическим полем состояниями ионов ТЬ3 +. Теория квантового анализа, предполагающей сочетание аналитических и численных методов, позволила нам количественно описать наблюдаемые магнитные и магнитоэлектрические свойства TbAl3 (BO3) 4.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Boldyrev K. N., Stanislavchuk T. N., Sirenko A. A., Bezmaternykh L. N., Popova M. N.
Заглавие : Coupling between phonon and crystal-field excitations in multiferroic PrFe3(BO3)4
Коллективы : Russian Scientific Foundation [14-12-01033]; President of Russian Federation [MK-1700.2013.2]; U.S. Department of Energy [DE-FG02-07ER46382, DE-AC02-98CH10886]
Место публикации : Phys. Rev. B: American Physical Society, 2014. - Vol. 90, Is. 12. - Ст.121101. - ISSN 1098-0121, DOI 10.1103/PhysRevB.90.121101. - ISSN 1550-235X
Примечания : Cited References: 35. - This research was supported by the Russian Scientific Foundation under Grant No. 14-12-01033, the President of Russian Federation (MK-1700.2013.2; K.N.B.), and the U.S. Department of Energy under Grant No. DE-FG02-07ER46382 (experiments at U4-IR beamline NSLS-BNL; T.N.S. and A.A.S.). The National Synchrotron Light Source is operated as a User Facility for the U.S. Department of Energy under Contract No. DE-AC02-98CH10886. M.N.P. thanks B. Z. Malkin for drawing her attention to the work [33] and for helpful discussions.
Предметные рубрики: MAGNETOELECTRIC PROPERTIES
GROUND-STATE
SM
Аннотация: Far-infrared reflection and ellipsometry measurements on multiferroic PrFe3(BO3)4 and SmFe3(BO3)4 single crystals were used to investigate the interaction between lattice phonons and electronic excitations associated with 4f crystal-field transitions. A temperature-dependent interference between two types of excitations was observed in PrFe3(BO3)4 in which the frequency of 4f crystal-field electronic excitation of Pr3+ falls into the TO-LO frequency interval of the optical phonon mode near 50 cm−1 (1.5 THz). Experimental data were explained on the basis of a theoretical model of coupled electron-phonon modes. The fitting procedure revealed the value 14.8 cm−1 for the electron-phonon coupling constant. This rather large value points to an essential role played by the electron-phonon interaction in the physics of multiferroics.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M. Y., Mitskan V. A., Korovushkin M. M.
Заглавие : Anomalous superconductivity and superfluidity in repulsive fermion systems
Место публикации : Phys. Usp.: Turpion, 2015. - Vol. 58, Is. 8. - P.733-761. - ISSN 10637869 (ISSN), DOI 10.3367/UFNe.0185.201508a.0785
Примечания : Cited References: 369. - We are grateful to M A Baranov, A V Chubukov, D V Efremov, M V Feigel'man, V V Kabanov, K I Kugel', M S Marienko, N M Plakida, N V Prokorev, A Ya Tzalenchuk, and V V Val'kov for the fruitful discussions and constant attention to our work. The work was supported by the Russian Foundation for Basic Research (project nos. 14-02-00058 and 14-02-31237). M Yu K thanks the Program of Basic Research of the National Research University Higher School of Economics for support. The work of MM K was supported by grant of the President of the Russian Federation (SP-1361.2015.1) and the Dinasty Foundation
Предметные рубрики: HEXAGONAL BORON-NITRIDE
SCANNING-TUNNELING-MICROSCOPY
2-DIMENSIONAL HUBBARD-MODEL
HIGH-TC SUPERCONDUCTIVITY
ELECTRON-ENERGY SPECTRUM
P-WAVE SUPERCONDUCTIVITY
DOUBLE-LAYER GRAPHENE
2D KONDO-LATTICE
GROUND-STATE
TRANSITION-TEMPERATURE
Ключевые слова (''Своб.индексиров.''): anomalous superconductivity--kohn-luttinger mechanism--superfluidity--repulsive fermi gas--hubbard and t-jmodel--shubin vonsovsky model--graphene monolayer--graphene bilayer
Аннотация: We discuss the mechanisms of unconventional superconductivity and superfluidity in 3D and 2D fermionic systems with purely repulsive interaction at low densities. We construct phase diagrams of these systems and find the areas of the superconducting state in free space, as well as on the lattice in the framework of the Fermi-gas model with hard-core repulsion, the Hubbard model, the Shubin-Vonsovsky model, and the t-J model. We demonstrate that the critical superconducting temperature can be greatly increased in the spin-polarized case or in a two-band situation already at low densities. The proposed theory is based on the Kohn-Luttinger mechanism or its generalizations and explains or predicts anomalous p-, d-, and f-wave pairing in various materials, such as high-temperature superconductors, the idealized monolayer and bilayer of doped graphene, heavy-fermion systems, layered organic superconductors, superfluid 3He, spin-polarized 3He mixtures in 4He, ultracold quantum gases in magnetic traps, and optical lattices.
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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) : Val'kov V. V., Mitskan V. A.
Заглавие : Magnetic-field-induced phase transition in a two-dimensional quantum magnet with plaquette distortion
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 105, Is. 1. - P90-93. - ISSN 1063-7761, DOI 10.1134/S1063776107070199
Примечания : Cited References: 10
Предметные рубрики: GROUND-STATE
CRYSTALS
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--magnetic field effects--magnets--phase diagrams--problem solving--spectrum analysis--plaquette distortion--quantum heisenberg magnet--quantum transition--two-dimensional quantum magnet--phase transitions
Аннотация: Magnetic field effect on the structure of the ground state of a two-dimensional quantum Heisenberg magnet is analyzed. A plaquette representation is used to solve the self-consistent problem and calculate the collective excitation spectrum in a magnetic field. Conditions are found for quantum transition between non-magnetic and oblique antiferromagnetic phases. The change in the ground state of the system is associated with disappearance of the gap in the spin excitation spectrum. Effects of frustration and magnetic field on the spectrum are analyzed. A phase diagram of stable singlet and magnetically ordered phases is presented.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Petrakovskii G. A., Bezmaternykh L. N., Bayukov O. A., Popov M. A., Schefer J., Neidermayer C., Aleshkevich P., Szymczak R.
Заглавие : Magnetic structure and magnetic excitations in the two-dimensional spin system of the Cu3B2O6 compound
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 7. - P1315-1320. - ISSN 1063-7834, DOI 10.1134/S1063783407070207
Примечания : Cited References: 21
Предметные рубрики: LONG-RANGE ORDER
HEISENBERG-MODEL
GROUND-STATE
GAP
ANTIFERROMAGNET
SRCU2(BO3)(2)
CUGEO3
CHAINS
CAV4O9
Аннотация: This paper reports on the results of measurements of the magnetic susceptibility, heat capacity, neutron scattering, muon spin relaxation, and electron paramagnetic resonance in Cu3B2O6 for the study of the ground state of the spin system of this compound. The results obtained suggest that, at a temperature of 10 K, the spin subsystem of the crystal, which consists of single spins and clusters of pairs and fours of spins interacting with one another, undergoes a transition to a state representing a superposition of the singlet (for clusters) and magnetically ordered (for single spins) states.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo investigation of the 2D Heisenberg model with S=1/2
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 1999. - Vol. 41, Is. 1. - P103-107. - ISSN 1063-7834, DOI 10.1134/1.1130737
Примечания : Cited References: 33
Предметные рубрики: SQUARE-LATTICE
GROUND-STATE
SPIN-CORRELATIONS
ANTIFERROMAGNET
LA2CUO4
EU2CUO4
ENERGY
ORDER
Аннотация: The two-dimensional (2D) Heisenberg model with anisotropic exchange (Delta=1-J(x)/J(z)) and S=1/2 is investigated by the quantum Monte Carlo method. The energy, susceptibility, specific heat, spin-spin correlation functions, and correlation radius are calculated. The sublattice magnetization (sigma) and the Neel temperature of the anisotropic antiferromagnet are logarithmic functions of the exchange anisotropy: 1/sigma + 1 + 0.13(1) ln(1/Delta). Crossover of the static magnetic structural factor as a function of temperature from power-law to exponential occurs for T(c)/J approximate to 0.4. The correlation radius can be approximated by 1/xi =2.05T(1.0(6))/exp(1.0(4)/ T). For La(2)CuO(4) the sublattice magnetization is calculated as sigma=0.45, the exchange is J=(1125=1305) K; for Er(2)CuO(4)J similar to 625 K and the exchange anisotropy Delta similar to 0.003. The temperature dependence of the static structural magnetic factor and the correlation radius above the Neel temperature in these compounds can be explained by the formation of topological excitations (spinons). (C) 1999 American Institute of Physics. [S1063-7834(99)02401-6].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Modeling a dimer state in CuGeO3 in the two-dimensional anisotropic Heisenberg model with alternated exchange interaction
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 1997. - Vol. 85, Is. 6. - P1196-1203. - ISSN 1063-7761, DOI 10.1134/1.558393
Примечания : Cited References: 33
Предметные рубрики: SPIN-PEIERLS TRANSITION
HIGH MAGNETIC-FIELDS
COMPOUND CUGEO3
GROUND-STATE
SYSTEMS
NEUTRON
Аннотация: The two-dimensional Heisenberg spin-1/2 model with alternated exchange interaction along the c axis and an anisotropic distribution of the exchange interaction in the lattice, J(b)/J(c)=0.1, is examined. A quantum Monte Carlo method is used to calculate the phase diagrams of the antiferromagnet, the dimer state in a plane, the value of the alternation delta of the exchange interaction, and the anisotropy Delta=1-J(xy)/J(z) of the exchange interaction, Delta similar to delta(0.58(6)). The following characteristics are calculated for Delta=0.25: the dependence of the temperature of the dimer-state-paramagnet transition on the alternation of the exchange interaction, T-c(delta)=0.55(4(delta-0.082(6))(0.50(3)), the singlet-triplet energy gap, and the dependence of the magnetization on the external field for some values of delta. The value of the exchange interaction, J(c)=127 K, the alternation of the exchange interaction, delta=0.11J(c), and the correlation radius along the c axis, xi(c) approximate to 28c, are determined. Finally, it is found that the temperature dependence of the susceptibility and the specific heat are in good agreement with the experimental data. (C) 1997 American Institute of Physics. [S1063-7761(97)01912-4].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Berman G. P., Bulgakov E. N., Campbell D. K., Gubernatis J. E., Sadreev A. F., Wang X. D.
Заглавие : Phase transition in the one-dimensional quantum discrete phi(4)-phi(2) model
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 1997. - Vol. 56, Is. 18. - P11518-11530. - ISSN 0163-1829, DOI 10.1103/PhysRevB.56.11518
Примечания : Cited References: 16
Предметные рубрики: FRENKEL-KONTOROVA MODEL
FIELD-THEORY
GROUND-STATE
FLUCTUATIONS
Аннотация: We consider the ground-state phase transition from broken to restored phases of the one-dimensional quantum discrete phi(4)-phi(2) model as a function of two parameters: the strength of the quantum fluctuations (measured by a dimensionless Planck constant (h) over bar), and the classical dimensionless coupling parameter gamma, which characterizes the strength of interaction of the neighboring atoms. We introduce several distinct variational methods based on self-consistent phonons and soliton wave functions, and compare their predictions for the phase diagram with the (numerically exact) results of previous quantum Monte Carlo simulations. Our calculations show that in the region of weak coupling (gamma 1), both the ''tunneling soliton'' and the ''two-level'' approaches provide good approximations to the true result. In the intermediate coupling region (gamma(c) gamma 1), the method of self-consistent phonons gives a satisfactory description of phase transition. We also compare and contrast our results with previously published approximate methods, and discuss problems for further investigation. [S0163-1829(97)06242-5].
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Mitskan V. A., Petrakovskii G. A.
Заглавие : The magnetoelastic mechanism of singlet phase formation in a two-dimensional quantum antiferromagnet
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 2. - P234-247. - ISSN 1063-7761, DOI 10.1134/S106377610602004X
Примечания : Cited References: 18
Предметные рубрики: GROUND-STATE
SPIN
TRANSITION
CUGEO3
MODEL
Ключевые слова (''Своб.индексиров.''): crystal lattices--elasticity--mathematical models--oscillations--phase diagrams--phase transitions--quantum theory--two dimensional--atomic representation--magnetoelastic mechanism--quantum antiferromagnets--singlet phase formation--antiferromagnetic materials
Аннотация: A model describing the second-order phase transition with respect to the magnetoelastic coupling parameter from the anti ferromagnetic (AFM) to the singlet state in a two-dimensional quantum magnet on a square lattice is proposed. The spectrum of elementary excitations in the singlet and AFM phases is calculated using an atomic representation, and the evolution of transverse and longitudinal branches of this spectrum is studied in the vicinity of the transition point. It is established that the AFM to singlet phase transition is related to softening of the longitudinal branch of oscillations. In the singlet phase, the gap plays the role of a parameter characterizing the distance to the phase transition point. It is shown that the spectrum of transverse oscillations in the AFM phase corresponds to the Goldstone boson. Based on an analysis of the stability of the spectrum of elementary excitations, a phase diagram is constructed that determines the regions of the existence of phases with plaquette-deformed lattices.
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