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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : OVCHINNIKOV S. G.
Заглавие : EFFECT OF SUBSTITUTIONAL IMPURITY SPECIES ON THE SUPPRESSION OF MAGNETIC-PROPERTIES OF WEAKLY DOPED COPPER OXIDES
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1994. - Vol. 36, Is. 5. - P1307-1310. - ISSN 0367-3294
Примечания : Cited References: 16
Предметные рубрики: ELECTRONIC-STRUCTURE
SUPERCONDUCTIVITY
LA2CUO4
EXCITATIONS
SPECTRA
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Modification of magnetic and superconducting properties of layered cuprates due to copper substitution for zinc and nickel
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1995. - Vol. 37, Is. 12. - P3645-3654. - ISSN 0367-3294
Примечания : Cited References: 28
Предметные рубрики: ELECTRONIC-STRUCTURE
LA2CUO4
LA2-XSRXCUO4
EXCITATIONS
DENSITY
PLANE
NI
WOS
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Avramov P. V., Ovchinnikov S. G.
Заглавие : Effects of the intense electron correlations on the shape of x-ray CuK absorption spectra of La2-xSrxCuO4
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1995. - Vol. 108, Is. 4. - P.1479-1488. - ISSN 0044-4510
Примечания : Cited References: 28
Предметные рубрики: HIGH-TC SUPERCONDUCTIVITY
EDGE STRUCTURE
LA2CUO4
SATELLITES
ALPHA
EXCITATIONS
COPPER
OXIDES
STATE
SHAKE
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shalaev V. M., Poliakov E. Y., Markel V. A.
Заглавие : Small-particle composites .2. Nonlinear optical properties
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 1996. - Vol. 53, Is. 5. - P2437-2449. - ISSN 0163-1829, DOI 10.1103/PhysRevB.53.2437
Примечания : Cited References: 45
Предметные рубрики: FRACTAL CLUSTERS
RAMAN-SCATTERING
SUSCEPTIBILITY
CONDUCTIVITY
EXCITATIONS
COLLOIDS
LIGHT
Аннотация: Strong fluctuations of local fields may result in very large optical nonlinearities in small-particle composites. Enhancement associated with particle clustering is found for a number of optical processes, including four-wave mixing (FWM), third-harmonic generation (THG), Raman scattering, and nonlinear refraction and absorption in Kerr media. Field fluctuations and optical nonlinear susceptibilities are especially large in fractal clusters. The enhancement of optical processes is expressed in terms of the resonant linear absorption by collective dipolar eigenmodes in a cluster, and quality factors, q, of the modes (q much greater than 1). It is shown that the susceptibility of a composite material consisting of random small-particle clusters is proportional to q(3) for Raman scattering and the Kerr optical nonlinearity, and to q(4) and q(6) for THG and FWM, respectively. For all of these processes, a spectral dependence of the effective susceptibility is found. Broad-scale numerical simulations of the optical response in small-particle composites are performed to complement the theory. The simulations are in reasonable agreement with available experimental data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I., Maradudin A. A.
Заглавие : Wave spectrum of multilayers with finite thicknesses of interfaces
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2000. - Vol. 62, Is. 3. - P2181-2184. - ISSN 0163-1829, DOI 10.1103/PhysRevB.62.2181
Примечания : Cited References: 24
Предметные рубрики: SPIN
EXCITATIONS
MEDIA
Аннотация: To describe a multilayer structure with arbitrary thicknesses of the interfaces between layers, we introduce a model in which the dependence of a material parameter along the axis of such a superlattice is described by a Jacobian elliptic sine function. Depending on the value of the modulus kappa of the elliptic function, the model describes the limiting cases of multilayers with sharp interfaces (kappa=1, d/l=0, where d is the thickness of the interface, l is the period of the superlattice) and of sinusoidal superlattices (kappa=0, d/l=1/4), as Well as all intermediate situations. We investigate the wave spectrum in such a superlattice. The dependences of the widths of the gaps in the spectrum at the boundaries of ail odd Brillouin zones on the ratio d/l are found. It is shown that the thicknesses of the interfaces can be determined if the experimental value of the relation between the widths of the first gap Delta v(1) and any other gap Delta v(n) is known.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Static and dynamic magnetic properties of coupled spin-1/2 antiferromagnetic chains
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2000. - Vol. 12, Is. 37. - P.8191-8207. - ISSN 0953-8984, DOI 10.1088/0953-8984/12/37/316
Примечания : Cited References: 21
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
SYSTEMS
SUSCEPTIBILITY
EXCITATIONS
SR2CUO3
CA2CUO3
KCUF3
Ключевые слова (''Своб.индексиров.''): computational methods--copper compounds--correlation methods--functions--magnetic field effects--magnetic properties--magnetization--monte carlo methods--quantum theory--specific heat--thermal effects--excitation spectroscopy--interchain coupling--intrachain couplings--mean-field approximation--spin-spin correlation function--spinons--antiferromagnetic materials
Аннотация: Calculations of the thermodynamic quantities, and the spectra of spinons, triplet excitations, and two-particle spin-singlet (Delta S-z = 0, +/- 1) excitations for a weakly coupled antiferromagnetic S = 1/2 spin chain are made using a mean-field approximation for the interchain couplings (J(2)) by the quantum Monte Carlo method. The mass gaps in these excitation spectra are estimated as functions of the interchain coupling. The critical held H-c, and the temperatures at which the spinon and singlet gaps close (T-1 and T-2, respectively) are obtained. Some peculiarities of the staggered magnetization, the specific heat, and the spin-spin correlation function are found at T-1 = 0.9J(2), T-2 = 1.5J(2), H-c = 3.8J(2), as determined by linear function fitting for J(2)/J(1) 0.15 The intrachain and interchain couplings, and the staggered magnetization for KCuF3, Sr2CuO3, and Ca2CuO3 are estimated, and mass gaps are predicted to exist in the spectra of the spinons and the singlet two-particle excitations.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G., Borisov A. A., Goryachev E. G.
Заглавие : Evolution of the band structure of quasiparticles with doping in copper oxides on the basis of a generalized tight-binding method
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2000. - Vol. 91, Is. 2. - P369-383. - ISSN 1063-7761, DOI 10.1134/1.1311997
Примечания : Cited References: 45
Предметные рубрики: T-J MODEL
CUPRATE SUPERCONDUCTORS
ELECTRONIC-STRUCTURE
EXCITATIONS
DEPENDENCE
TEMPERATURE
DERIVATION
SR2CUO2CL2
SPECTRUM
DENSITY
Аннотация: Two methods for stabilizing the two-hole B-3(1g) state as the ground state instead of the Zhang-Rice singlet are determined on the basis of an orthogonal cellular basis for a realistic multiband pd model of a CuO2 layer and the dispersion relations for the valence band top in undoped and doped cases are calculated. In the undoped case, aside from the valence band, qualitatively corresponding to the experimental ARPES data for Sr2CuO2Cl2 and the results obtained on the basis of the t-t'-J model, the calculations give a zero-dispersion virtual level at the valence band top itself. Because of the zero amplitude of transitions forming the virtual level the response corresponding to it is absent in the spectral density function. In consequence, the experimental ARPES data do not reproduce its presence in this antiferromagnetic undoped dielectric. A calculation of the doped case showed that the virtual level transforms into an impurity-type band and acquires dispersion on account of the nonzero occupation number of the two-hole states and therefore should be detected in ARPES experiments as a high-energy peak in the spectral density. The computed dispersion dependence for the valence band top is identical to the dispersion obtained by the Monte Carlo method, and the ARPES data for optimally doped Bi2Sr2CaCu2O8 + delta samples. The data obtained also make it possible to explain the presence of an energy pseudogap at the symmetric X point of the Brillouin band of HTSC compounds. (C) 2000 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Vorotynov A. M., Ovchinnikov S. G., Rudenko V. V., Sudakov A. N.
Заглавие : Magnetic anisotropy of antiferromagnet (CH3)(4)NMnCl3
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2000. - Vol. 42, Is. 7. - P1313-1316. - ISSN 1063-7834, DOI 10.1134/1.1131384
Примечания : Cited References: 14
Предметные рубрики: EXCITATIONS
Аннотация: The parameters of the electron paramagnetic resonance (EPR) spectra of S ion pairs in diamagnetic crystals are analyzed. A relation between the spin Hamiltonian constants is established for solitary ions and pairs for (CH3)(4)NCdCl3:Mn2+ crystals. In contrast to solitary ions, an additional contribution (which is a linear function of the exchange field) to the "single-ion" spin Hamiltonian constants appears in the case of pairs. It is shown that anisotropic exchange mechanisms do not play a significant part in the formation of the axial constant of the spin Hamiltonian for this crystal. Some aspects of the method of studying "single-ion" anisotropy predicted by the two-ion model are developed with the help of an isostructural diamagnetic analog with impurity concentration of the paramagnetic ions of a magnetically concentrated substance sufficiently high for observing the EPR spectrum of the pairs. It is found that the microscopic quantities determined partially from the EPR spectra for pairs and solitary Mn2+ ions in (CH3)(4)NCdCl3 are in accord with the experimental value of the effective field for the (CH3)(4)NMnCl3 crystal anisotropy which can be described primarily by the dipole and "single-ion" mechanisms of the exchange origin. (C) 2000 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo investigation of the magnetic properties of weakly interacting antiferromagnetic chains with an alternating exchange interaction with spin S=1/2
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2000. - Vol. 90, Is. 1. - P194-201. - ISSN 1063-7761, DOI 10.1134/1.559075
Примечания : Cited References: 35
Предметные рубрики: PEIERLS COMPOUND CUGEO3
MAGNON DISPERSION
BI2CUO4
EXCITATIONS
RESONANCE
SYSTEMS
SCATTERING
DYNAMICS
NEUTRON
PHASE
Аннотация: An approximation dependence of the spontaneous magnetic moment at a site, sigma/sigma(0) - 1 = 0.71(6)delta(2.5(2)), and the antiferromagnet-singlet state phase boundary, J(2)/J(1) = 0.52(3)delta, are determined by the quantum Monte Carlo method in the self-consistent sublattice molecular field approximation for weakly interacting (J(2)) antiferromagnetic chains with spin S = 1/2 and alternating exchange interaction (J(1) +/- delta). The Neel temperature and a number of critical temperatures which could be related with the filling energy of two singlets (Delta S-z = 0) and one triplet (Delta S-z= 1) spin bands, each of which is split by the sublattice field (h(x,y)not equal h(z)) into two subbands, are determined on the basis of the computed correlation radii of the two- and four-spin correlation function, the squared total spin (S-z)(2) with respect to the longitudinal components, the dimerization parameter, and the correlation functions between the nearest neighbors with respect to longitudinal and transverse spin components. On the basis of the Monte Carlo calculations, the critical temperatures and possible energy gaps at the band center are determined for the antiferromagnets CuWO4 and Bi2CuO4 and for the singlet compounds (VO)(2)P2O7 and CuGeO3 , agreeing satisfactorily with existing results, and new effects are also predicted. (C) 2000 MAIK "Nauka / Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Laletin O. N.
Заглавие : Waves in a superlattice with arbitrary interlayer boundary thickness
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 12. - P2292-2300. - ISSN 1063-7834, DOI 10.1134/1.1841396
Примечания : Cited References: 34
Предметные рубрики: PERIODIC STRUCTURES
RAYLEIGH-WAVES
LAYERED MEDIUM
ELASTIC-WAVES
SPIN-WAVES
SPECTRUM
MEDIA
PROPAGATION
EXCITATIONS
MULTILAYERS
Аннотация: The transmittance D(omega), reflectance R(omega), and dispersion omega(k) are investigated for waves of various nature propagating through a one-dimensional superlattice (multilayer structure) with arbitrary thickness of the interlayer boundary. The dependences of the band gap widths Deltaomega(m) and their positions in the wave spectrum of the superlattice on the interlayer boundary thickness d and the band number m are calculated. Calculations are performed in terms of the modified coupled-mode theory (MCMT) using the frequency dependence of R(omega), as well as in the framework of perturbation theory using the function omega(k), which made it possible to estimate the accuracy of the MCMT method; the MCMT method is found to have a high accuracy in calculating the band gap widths and a much lower accuracy in determining the gap positions. It is shown that the m dependence of Deltaomega(m) for electromagnetic (or elastic) waves is different from that for spin waves. Furthermore, the widths of the band gaps with m = 1 and 2 are practically independent of d, whereas the widths of all gaps for m 2 depend strongly on d. Experimental measurements of these dependences allow one to determine the superlattice interface thicknesses by using spectral methods. (C) 2004 MAIK "Nauka/Interperiodica".
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11.

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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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Avramov P. V., Sorokin P. B., Fedorov A. S., Fedorov D. G., Maeda Y.
Заглавие : Band-gap unification of partially Si-substituted single-wall carbon nanotubes
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2006. - Vol. 74, Is. 24. - Ст.245417. - ISSN 1098-0121, DOI 10.1103/PhysRevB.74.245417
Примечания : Cited References: 72
Предметные рубрики: SILICON-CARBIDE NANOTUBES
DENSITY-FUNCTIONAL THEORY
TOTAL-ENERGY CALCULATIONS
WAVE BASIS-SET
ELECTRONIC-STRUCTURE
AB-INITIO
NANORODS
EXCITATIONS
TRANSITION
NANOWIRES
Аннотация: The atomic and electronic structure of a set of pristine single wall SiC nanotubes as well as Si-substituted carbon nanotubes and a SiC sheet was studied by the local-density approximation (LDA) plane wave band structure calculations. Consecutive substitution of carbon atoms by Si leads to a gap opening in the energetic spectrum of the metallic (8,8) SWCNT with approximately quadratic dependence of the band gap upon the Si concentration. The same substitution for the semiconductor (10,0) single wall carbon nanotubes (SWCNT) results in a band gap minimum (0.27 eV) at similar to 25% of Si concentration. In the Si concentration region of 12-18 %, both types of nanotubes have less than 0.5 eV direct band gaps at the Gamma-Gamma point. The calculation of the chiral (8,2) SWSi0.15C0.85NT system gives a similar (0.6 eV) direct band gap. The regular distribution of Si atoms in the atomic lattice is by similar to 0.1 eV/atom energetically preferable in comparison with a random distribution. Time dependent density functional theory (DFT) calculations showed that the silicon substitution sufficiently increases (roughly by one order of magnitude) the total probability of optical transitions in the near infrared region, which is caused by the opening of the direct band gap in metallic SWCNTs, the unification of the nature and energy of the band gaps of all SWCNT species, the large values of Si3p parallel to r parallel to Si3s radial integrals and participation of Si3d states in chemical bonding in both valence and conductance bands.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S., Petrakovskii G. A., Miroshnichenko N. I.
Заглавие : Simulation of magnetic properties of the two-dimensional magnetic with anisotropic antiferromagnetic interactions and cluster ordering by quantum Monte Carlo
Место публикации : Phys. Lett. A: ELSEVIER SCIENCE BV, 2008. - Vol. 372, Is. 26. - P4722-4725. - ISSN 0375-9601, DOI 10.1016/j.physleta.2008.05.010
Примечания : Cited References: 12
Предметные рубрики: SPIN SYSTEM
EXCITATIONS
CU3B2O6
MODEL
Ключевые слова (''Своб.индексиров.''): anisotropic antiferromagnetic--cluster ordering--plateau of magnetization--modulated structure--exchange in cu3b2o6--anisotropic antiferromagnetic--cluster ordering--exchange in cu3b2o6--modulated structure--plateau of magnetization
Аннотация: Magnetic with anisotropic anti ferromagnetic exchange interactions and special topology of coupling in the square lattice with spins pairs ordering is studied by quantum Monte Carlo method. The antiferromagnetic order is found to be more stable as compared to spin liquid state. Exchange interactions and wave vector of structure modulation for Cu3B2O6 is estimated. Neel temperature versus strength of exchange in spin pair is calculated. Plateau and modulation of magnetic structure in field magnetization dependence is revealed. (C) 2008 Elsevier B.V. All rights reserved.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Korshunov M. M., Shneyder E. I.
Заглавие : Lifshits Quantum Phase Transitions and Rearrangement of the Fermi Surface upon a Change in the Hole Concentration in High-Temperature Superconductors
Коллективы : Presidium of the Russian Academy of Sciences [5.7]; Russian academy of Sciences; Russian Foundation for Basic Research [09-02-00127]
Разночтения заглавия :авие SCOPUS: Lifshits quantum phase transitions and rearrangement of the fermi surface upon a change in the hole concentration in high-temperature superconductors
Место публикации : J. Exp. Theor. Phys. - 2009. - Vol. 109, Is. 5. - Pю775-785. - ISSN 1063-7761, DOI 10.1134/S1063776109110077
Примечания : Cited References: 71. - The authors thank A. A. Kordyuk for discussion of the results and T. M. Ovchinnikova for technical assistance in data processing.This study was supported by the program "Quantum Physics of Condensed Media" of the Presidium of the Russian Academy of Sciences (project no. 5.7), integrated project no. 40 of the Siberian Branch-Ural Division of the Russian academy of Sciences, and the Russian Foundation for Basic Research (project no. 09-02-00127).
Предметные рубрики: T-J MODEL
CORRELATED ELECTRONS
COPPER OXIDES
SPECTRUM
PSEUDOGAP
METAL
FLUCTUATIONS
EXCITATIONS
INSULATOR
SYSTEMS
Ключевые слова (''Своб.индексиров.''): critical points--cuprates--electron heat--electron structures--experimental data--high-t--layered cuprates--low temperatures--normal phase--quantum oscillations--quantum phase transitions--sign reversal--strong correlation--copper compounds--electronic structure--equations of state--fermi surface--fermions--high temperature superconductors--hole concentration--superconductivity--surface structure--phase transitions
Аннотация: Changes in the electronic structure in the normal phase of high-T-c superconductors (HTSCs), viz., layered cuprates, are considered. The results of LDA + GTB calculations of the electron structure and the Fermi surface of La2-xSrxCuO4 one-layer cuprates with allowance for strong correlations are compared with ARPES and quantum oscillations data. Two critical points x(c1) and x(c2) are discovered at which the rearrangement of the Fermi surface takes place. In the vicinity of these points, changes in the thermodynamic properties at low temperatures are determined using the Lifshits ideology concerning 2.5-order quantum phase transitions. A singularity delta(C/T) proportional to (x-x(e))(1/2) in the electron heat capacity agrees well with the available experimental data in the vicinity of x(c1)approximate to 0.15. Sign reversal of the Hall constant upon doping is also considered qualitatively.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Zakharova E. V., Nekrasov I. A., Pchelkina Z. V., Ovchinnikov S. G.
Заглавие : The Fermi surface and the role of electronic correlations in Sm2-xCexCuO4
Коллективы :
Разночтения заглавия :авие SCOPUS: The Fermi surface and the role of electronic correlations in Sm 2-xCexCuO4
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2010. - Vol. 22, Is. 1. - Ст.15701. - ISSN 0953-8984, DOI 10.1088/0953-8984/22/1/015701
Примечания : Cited References: 35. - We would like to thank A A Kordyuk and I Eremin for useful discussions. The authors acknowledge support from RFBR (grants 08-02-00021, 10-02-00662, 08-02-91200 and 07-02-00226), the RAS programs on 'Low temperature quantum phenomena', 'Quantum physics of condensed matter' and 'Strongly correlated electrons solids', President of Russia (grants MK-614.2009.2 (IN) and MK-3227.2008.2 (ZP)), Scientific School (grant SS-1929.2008.2), Interdisciplinary UB-SB RAS project, Dynasty Foundation (ZP) and Russian Science Support Foundation (IN).
Предметные рубрики: T-C SUPERCONDUCTOR
IN-GAP STATES
SPIN CORRELATIONS
BAND
LA2-XSRXCUO4
EXCITATIONS
TRANSITION
EVOLUTION
SM2CUO4
OXIDES
Ключевые слова (''Своб.индексиров.''): antiferromagnetics--doping evolution--electron-doped--electronic correlation--emery model--experimental data--generalized tight bindings--high-t--hybrid scheme--magnetic orders--spin-liquid--tight binding model--two-regime--antiferromagnetism--cerium--cerium compounds--copper oxides--corundum--doping (additives)--fermi surface--fermions--tin--surfaces
Аннотация: Using a LDA + GTB (local density approximation + generalized tight-binding) hybrid scheme we investigate the band structure of the electron-doped high-T-c material Sm2-xCexCuO4. Parameters of the minimal tight-binding model for this system (the so-called three-band Emery model) were obtained within the NMTO (Nth-order muffin-tin orbital) method. The doping evolution of the dispersion and the Fermi surface in the presence of electronic correlations was investigated in two regimes of magnetic order: short-range (spin-liquid) and long-range (antiferromagnetic metal). Each regime is characterized by the specific topologies of the Fermi surfaces and we discuss their relation to recent experimental data.
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16.

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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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pisarev R. V., Kalashnikova A. M., Schops O., Bezmaternykh L. N.
Заглавие : Electronic transitions and genuine crystal-field parameters in copper metaborate CuB2O4
Разночтения заглавия :авие SCOPUS: Electronic transitions and genuine crystal-field parameters in copper metaborate CuB 2O 4
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2011. - Vol. 84, Is. 7. - Ст.75160. - ISSN 1098-0121, DOI 10.1103/PhysRevB.84.075160
Примечания : Cited References: 65. - Useful discussions with W. Weber on crystal-field splitting of 3d states in cuprates are appreciated. We thank H.-J. Weber for the help in using Cary 2300 spectrophotometer. This work is supported by the Russian Foundation for Basic Research (project No. 09-02-00070) and Federal Agency for Science and Innovations (Grant No. 02.740.11.0384). A. M. K. acknowledges the financial support from the Committee for Science and Higher Education of the Government of Saint Petersburg.
Предметные рубрики: OPTICAL-ABSORPTION
PHASE-DIAGRAM
CUGEO3
SPECTRUM
SUPERCONDUCTORS
EXCITATIONS
SR2CUO2CL2
SCATTERING
LA2CUO4
CUPRATE
Аннотация: We present and analyze high-resolution alpha-, sigma-, and pi-polarized absorption spectra related to d-d electronic transitions in tetragonal metaborate CuB2O4 where copper Cu2+ ions occupy two crystallographically distinct 4b and 8d positions. The spectra are characterized by exceptionally rich fine structure in the spectral range of 1.4-2.4 eV. Six zero-phonon (ZP) lines originating from the electronic transitions within the Cu2+ ions in both positions are distinguished and identified. Symmetry analysis explains polarization properties of the ZP lines in the 8d positions but only partially explains them in the 4b positions. Reliable assignment of all six ZP lines to specific transitions allowed us to calculate genuine cubic Dq and tetragonal Ds and Dt crystal-field parameters for both positions. We show that the (3r(2) - z(2)) state, the energy of which is the measure of the Jahn-Teller splitting, is the highest 3d state for both types of Cu2+ ion positions. Using the obtained crystal-field parameters as the reference values, we estimated Dq, Ds, and Dt for several other cuprates with different Cu-O bond lengths. In particular, the 3d level splitting in La2CuO4, Nd2CuO4, CuGeO3, Sr2CuO2Cl2, and Cu3B7O13Cl was analyzed. Our estimates suggest that the Jahn-Teller splitting in some of these cuprates is larger than it was assumed previously.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M., Barabanov A. F.
Заглавие : Effect of the concentration-dependent spin-charge correlations on the evolution of the energy structure of the 2D Emery model
Коллективы : Presidium of the Russian Academy of Sciences; Russian Foundation for Basic Research [13-02-00909, 13-02-00523, 13-02-98013_r-sibir]; Dynasty foundation
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 118, Is. 6. - P.959-970. - ISSN 1063-7761, DOI 10.1134/S1063776114060223. - ISSN 1090-6509
Примечания : Cited References: 48. - This work was supported by the program "Quantum Physics of Mesoscopic and Disordered Systems" of the Presidium of the Russian Academy of Sciences, the Russian Foundation for Basic Research (project nos. 13-02-00909, 13-02-00523, and 13-02-98013_r-sibir), and the Dynasty foundation.
Предметные рубрики: SADDLE-POINT SINGULARITY
CUPRATE SUPERCONDUCTORS
FERMI-SURFACE
ANTIFERROMAGNETIC CORRELATIONS
NORMAL-STATE
Bi2Sr2CaCu2O8+δ
EXCITATIONS
YBa2Cu3O6.9
La2CuO4
YBa2Cu4O8
Аннотация: It is shown using the 2D Emery model that the strong coupling between the spin subsystem of copper ions in the singlet state and the subsystem of oxygen holes considerably reduces the spectral intensity of the correlation function for holes on the Fermi contour. Spin-charge correlations are manifested in the existence of two channels. The first channel is due to the p-d exchange coupling of spins of the oxygen and copper holes. The second channel appears as a result of spin-correlated hoppings, when the motion of holes over oxygen ions is accompanied by spin-flip processes (i.e., simultaneous changes in the spin projections of an oxygen hole and a copper ion). It is established as a result of self-consistent calculations that the allowance for the concentration dependence of spin correlators and multicenter spin-charge correlators appearing in the dispersion equation ensures a decrease in the energy of the system and considerably affects the evolution of the Fermi surface under hole doping.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Dzebisashvili D. M., Val'kov V. V., Barabanov A. F.
Заглавие : Fermi surface evolution in the ensemble of spin-polarized quasiparticles in La2 - xSrxCuO4
Место публикации : JETP Letters. - 2014. - Vol. 98, Is. 9. - P.528-533. - ISSN 0021-3640, DOI 10.1134/S0021364013220049. - ISSN 1090-6487
Примечания : Cited References: 36. - This work was supported by the Presidium of the Russian Academy of Sciences (program "Quantum Mesoscopic and Disordered Structures"), by the Russian Foundation for Basic Research (project nos. 13-02-00909, 13-02-00523, and 11-02-98007-Siberia), and by the Dynasty Foundation.
Предметные рубрики: SADDLE-POINT SINGULARITY
ANTIFERROMAGNETIC CORRELATIONS
CUPRATE SUPERCONDUCTORS
NORMAL-STATE
MODEL
BI2SR2CACU2O8+DELTA
YBA2CU3O6.9
LA2CUO4
EXCITATIONS
YBA2CU4O8
Аннотация: For the spin-fermion model, it has been shown that the concept of spin polarons makes it possible to reproduce fine details of the Fermi surface evolution in the nodal direction of La2-xSrxCuO4 occurring with changes in the doping level x. The physics here is determined by the spin-correlated hopping of charge carriers and by the doping dependence of the inverse magnetic correlation length. © 2013 Pleiades Publishing, Inc.
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20.

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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