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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhu J., Xia, Zhiguo, Zhang Y., Molokeev M. S., Liu Q.
Заглавие : Structural phase transitions and photoluminescence properties of Eu3+ doped Ca(2-x)BaxLaNbO6 phosphors
Место публикации : Dalton Trans.: Royal Society of Chemistry, 2015. - Vol. 44, Is. 42. - P.18536-18543. - ISSN 1477-9226, DOI 10.1039/c5dt03430b
Примечания : Cited References: 27. - The present work was supported by the National Natural Science Foundation of China (Grant No. 51272027, 51472028 and 51272242), Natural Science Foundations of Beijing (2132050), the Program for New Century Excellent Talents in the University of the Ministry of Education of China (NCET-12-0950), Beijing Nova Program (Z131103000413047), Beijing Youth Excellent Talent Program (YETP0635), and the Funds of the State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University (KF201306)
Предметные рубрики: Double-perovskite
Luminescence properties
Thermal-stability
Crystal-chemistry
Red phosphors
White LEDs
Symmetry
Band
Ta
Ln
Аннотация: Crystal structures of the series of double perovskites Ca(2-x)BaxLaNbO6:Eu3+ phosphors have been examined by powder X-ray diffraction and Rietveld refinements. Ca2LaNbO6 has a monoclinic (P21/n) and Ba2LaNbO6 has a monoclinic (C2/m) structure. The structural phases of Ca(2-x)BaxLaNbO6:Eu3+ samples are divided into three sections depending on different Ca/Ba ratios: (1) monoclinic phase (P21/n) as Ca2LaNbO6 in the range of x = 0-0.1, (2) mixed phases containing Ca2LaNbO6 and Ba2LaNbO6 between 0.15 and 1.2, and (3) monoclinic phase (C2/m) as Ba2LaNbO6 for x = 1.4-2. Eu3+ ions act as the structural probes to study the structural phase transitions, and the evolution of the photoluminescence properties and thermal stability behaviours has been also comparatively investigated depending on different structural symmetries from Ca2LaNbO6 to Ba2LaNbO6 phase. The strong red emission from 5D0-7F2 peaking at 618 nm can be found in Ca2LaNbO6:Eu3+ phosphors, which is attributed to the low crystal field effect of the activator ions located in the highly distorted [Lao8] polyhedra sites. The composition-optimized phosphors can find applications in white light emitting diodes (LEDs).
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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) : Ovchinnikov S. G., Shneyder E. I.
Заглавие : The Interplay of Phonon and Magnetic Mechanism of Pairing in Strongly Correlated Electron System of High-T-c Cuprates
Коллективы :
Разночтения заглавия :авие SCOPUS: The interplay of phonon and magnetic mechanism of pairing in strongly correlated electron system of high-T c cuprates
Место публикации : J. Supercond. Nov. Magn.: SPRINGER, 2010. - Vol. 23, Is. 5. - P733-736. - ISSN 1557-1939, DOI 10.1007/s10948-009-0633-z
Примечания : Cited References: 26. - This work is supported by the Presidium RAS program N 7 "Quantum physics of condensed matter," the integration project SORAN-UrORAN N 40, and the RFFI Grant 09-02-00127.
Предметные рубрики: PHASE-TRANSITIONS
OXIDE SUPERCONDUCTORS
SYMMETRY
COPPER
MODEL
BAND
BI2SR2CACU2O8+DELTA
LA2-XSRXCUO4
PB
Ключевые слова (''Своб.индексиров.''): high-t-c superconductivity--strong correlated electron systems--mechanisms of superconducting pairing--high-t c superconductivity--mechanisms of superconducting pairing--strong correlated electron systems--ab initio--buckling mode--correlated electron systems--critical temperatures--cuprates--fitting parameters--high-t--isotope effect--low energies--magnetic mechanisms--order of magnitude--phonon mode--strongly correlated electron system--strongly correlated electrons--superconducting pairing--superconductivity mechanism--type theory--buckling--copper compounds--electrons--isotopes--magnetic materials--phonons--superconductivity--superconducting magnets
Аннотация: We consider magnetic mechanism of superconducting pairing in the effective low energy t - t' - t '' - J* model with all parameters calculated ab initio. Interaction of strongly correlated electrons with different phonon modes is also incorporated. In a BCS type theory, the d(x2-y2) gap is given by a sum of magnetic and phonon contributions. The main contribution to the only fitting parameter G is determined by a competition of the breathing and buckling modes. Fitting the parameter G from the isotope effect, we obtain that magnetic and phonon contributions to the critical temperature T-c work together and are of the same order of magnitude.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Korshunov M. M., Zakharova E. V.
Заглавие : Temperature evolution of spin-polaron in-gap states in undoped antiferromagnetic cuprates
Коллективы :
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 50, Is. 8. - P1401-1406. - ISSN 1063-7834, DOI 10.1134/S1063783408080027
Примечания : Cited References: 26. - This work was supported by the Russian Foundation for Basic Research (project nos. 06-02-16100 and 0602- 90537-BNTS), the Presidium of the Russian Academy of Sciences (program "Quantum Macrophysics"), and INTAS (YS grant no. 05-109-4891).
Предметные рубрики: J MODEL
LA2-XSRXCUO4
SUPERCONDUCTORS
BAND
Аннотация: The temperature evolution of in-gap states created by the spin polaron effect and located within the gap with charge transfer between the valence and conduction bands is studied for the case of strong electron correlations using the t-t'-t ''-J model of antiferromagnetic undoped cuprates. The effect of temperature is taken into account by temperature renormalization of the magnon concentration, which is calculated using the Heisenberg model with inclusion of weak interlayer exchange and weak in-plane spin anisotropy, and by introducing a Lorentzian with a temperature-dependent half-width in the form corresponding to the marginal Fermi liquid model. With increasing temperature, the spectral weight of the in-gap state, which is proportional to the magnon concentration, grows leading to an increased intensity of the corresponding peak of the spectral function in all points of the Brillouin zone. At points (pi/2, pi/2) and (pi, 0), the main peak is approached by the satellite peak related to the in-gap band and, at points (0, 0) and (pi, pi), the peaks move away from each other.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuzmin E. V.
Заглавие : The ground state problem in the infinite-U Hubbard model
Место публикации : Phys. Solid State: AMER INST PHYSICS, 1997. - Vol. 39, Is. 2. - P169-178. - ISSN 1063-7834, DOI 10.1134/1.1130126
Примечания : Cited References: 36
Предметные рубрики: NAGAOKA FERROMAGNETIC STATE
INSTABILITY
HOLES
BAND
Аннотация: The problem of the ground state of the electronic system in the Hubbard model for U=infinity is discussed. The author investigates the normal (singlet or nonmagnetic) N state of the electronic system over the entire range of electron densities n less than or equal to 1. It is shown that the energy of the N state epsilon(0)((1))(n) in a one-particle approximation, such as (e.g.) the extended Hartree-Fock approximation, is lower than the energy of the saturated ferromagnetic FM state epsilon(FM)(n) for all n. The dynamic magnetic susceptibility is calculated in the random phase approximation, and it is shown that the N state is stable over the entire range of electron densities: The static susceptibility (omega=0) does not have a band singularity in the zero-wave vector limit q--0. A formally exact representation is obtained for the mass operator of the one-particle Green's function, and an approximation of this operator is proposed: M-k(E)similar or equal to lambda F(E), where lambda=n(1-n)/(1-n/2)z is the kinematic interaction parameter, z is the number of nearest neighbors, and F(E) is the total single-site Green's function. For an elliptical density of states the integral equation for F(E) is solved exactly, ad it is shown that the spectral intensity rigorously satisfies the sum rule. The calculated energy of the strongly correlated N state epsilon(0)(n)epsilon(FM)(n) for all n, and in light of this relationship the author discusses the hypothesis that the ground state of the system is the normal (singlet) state in the thermodynamic limit. The electron distribution function at T
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ovchinnikov S. G., Yakimov L. E.
Заглавие : The role of orbital ordering in the formation of electron structure in undoped LaMnO3 manganites in the regime of strong electron correlations
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 6. - P972-985. - ISSN 1063-7761, DOI 10.1134/S1063776106060112
Примечания : Cited References: 25
Предметные рубрики: COLOSSAL MAGNETORESISTIVE OXIDES
DOUBLE EXCHANGE
BAND
MODEL
Ключевые слова (''Своб.индексиров.''): computational methods--correlation methods--doping (additives)--electrons--ferromagnetic materials--lanthanum compounds--paramagnetic materials--intraatomic electron correlations--mott hubbard correlation gap--orbital ordering--paramagnetic phases--electronic structure
Аннотация: The electron structure of undoped LaMnO3 and slightly doped La1-xSrxMnO3 manganites has been calculated within the framework of a generalized tight binding method with explicit allowance for strong intra-atomic electron correlations. According to the results of these calculations, the ground state in orbitally disordered undoped LaMnO3 ferromagnets would be metallic despite the Mott-Hubbard correlation gap in the spectrum of quasiparticles. Owing to the orbital ordering, the insulating state is stabilized in both antiferromagnetic and paramagnetic phases. In-gap states of a polaron nature with a spectral weight proportional to the dopant concentration have been found near the top of the valence band in La1-xSrxMnO3. As the doping level increases, a metal state appears in the ferromagnetic phase, which has a metallic character for one spin subband and an insulating character for the other subband (representing the so-called half-metallic state).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Gavrichkov V. A., Korshunov M. M., Shneyder E. I.
Заглавие : Electron structure and electron-phonon interaction in the strongly correlated electron system of cuprates
Место публикации : Low Temp. Phys. - 2006. - Vol. 32, Is. 4-5. - P.483-488. - ISSN 1063-777X, DOI 10.1063/1.2199450; \b Физика низких температур
Примечания : Cited References: 37
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
HIGH-TC SUPERCONDUCTIVITY
C SUPERCONDUCTORS
J MODEL
BAND
REPRESENTATION
REGIME
OXIDES
Аннотация: The generalized tight-binding method presents a practical realization of the scheme that describes quasiparticles in a strongly correlated electron system and consists of exact intra-cell diagonalization of the model Hamiltonian and perturbative treatment of the inter-cell hoppings. In the present paper this method and its ab initio modification are applied to undoped and weakly doped HTSC cuprates. Results are in very good agreement with the experimental ARPES data on various compounds. Starting with a multiband p-d model the realistic effective low-energy Hamiltonian of strongly correlated electrons interacting with spin fluctuations and phonons is derived both for hole- and electron-doped systems. Without electron-phonon interaction the pure magnetic mechanism of pairing does not provide the correct value of T, even for single-layer La2-xSrxCuO4 and Nd2-xCexCuO4. (c) 2006 American Institute of Physics.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Density of hole-doped states in strongly correlated electron-systems of copper oxides
Разночтения заглавия :авие SCOPUS: Density of hole-doped states in strongly correlated electron systems of copper oxides
Место публикации : Phys. Rev. B. - 1994. - Vol. 49, Is. 14. - P.9891-9897. - ISSN 0163-1829, DOI 10.1103/PhysRevB.49.9891
Примечания : Cited References: 34
Предметные рубрики: DYNAMIC PROPERTIES
SUPERCONDUCTIVITY
GAP
LA2CUO4
BI2SR2CACU2O8
PHOTOEMISSION
SPECTROSCOPY
SPECTRA
MODEL
BAND
Аннотация: A generalized tight-binding method to calculate quasiparticle band structure and density of states in strongly correlated systems is presented. The band structures of undoped and weakly hole-doped CuO2 layer are calculated. The insulator gap has a charge transfer nature with a minor contribution from a Cu-O Coulomb interaction. Doping results in the appearance of an in-gap state with a simultaneous decrease of the density of states at the band edges in agreement with small cluster results and experimental data.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G., Shneider E. I.
Заглавие : Reconstruction of the Fermi surface of HTSC cuprates in a high magnetic field
Коллективы : Russian Foundation for Basic Research [09-02-00127]; Siberian Branch and the Ural Division, Russian Academy of Sciences [40]; Presidium of the Russian Academy of Sciences [5.7]
Место публикации : JETP Letters. - 2009. - Vol. 89, Is. 12. - P.632-637. - ISSN 0021-3640, DOI 10.1134/S002136400912008X
Примечания : Cited References: 19. - This work was supported by the Russian Foundation for Basic Research (project no. 09-02-00127), the Siberian Branch and the Ural Division, Russian Academy of Sciences (integration project no. 40), and the Presidium of the Russian Academy of Sciences (program no. 5.7).
Предметные рубрики: T-J MODEL
COPPER OXIDES
ELECTRON
SPECTRUM
BAND
Аннотация: The effect of a high magnetic field on the electronic structure of HTSC cuprates is considered. The study is performed in the t-t'-taEuro(3)-J* model, and the high magnetic field effect is taken into account not only as the Zeeman splitting of the one-electron levels, but also in the occupation numbers of the states with different spin projections and in the formation of the spin correlation functions. The field is assumed to be high enough to align all of the spins along the field. As a result, the Fermi surface reconstruction is obtained from four hole pockets about the nodal point (pi/2, pi/2) in the paramagnetic phase to a large hole pocket about the point (pi, pi) in the ferromagnetic phase. As the magnetic field strength decreases, a number of quantum phase transitions are revealed; they are manifested in the changed Fermi surface topology. The Fermi surface reconstruction with a decreasing field is qualitatively the same as that with an increasing doping degree in the absence of a magnetic field.
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