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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Second moment of multiple-quantum NMR and a time-dependent growth of the number of multispin correlations in solids
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 103, Is. 6. - P904-916. - ISSN 1063-7761, DOI 10.1134/S1063776106120089
Примечания : Cited References: 39
Предметные рубрики: NUCLEAR-MAGNETIC-RESONANCE
LINE-SHAPE
SPIN SYSTEMS
DYNAMICS
SPECTRA
COHERENCES
STATE
BEHAVIOR
CRYSTAL
MODEL
Ключевые слова (''Своб.индексиров.''): correlation methods--mathematical models--nuclear magnetic resonance spectroscopy--spectrum analysis--time series analysis--four-spin time correlation--multispin correlations--second moment--time power series--quantum theory
Аннотация: The time evolution of multispin correlations (the growth of the number of correlated spins as a function of time) can be observed directly using the multiple-quantum nuclear magnetic resonance spectroscopy of solids. A quantity related to this number, namely, the second moment n(2)(t) of the intensity distribution of coherences of different orders in the multiple-quantum spectrum can be calculated using the theory proposed in this work. An approach to the calculation of the four-spin time correlation function through which this moment is expressed is developed. The main sequences of contributions in the expansion of this function into a time power series are summed using the approximation of a large number of neighbors both for systems with a secular dipole-dipole interaction and for systems with a nonsecular effective interaction. An exponential dependence of n(2)(t) is obtained. The value of n(2)(t) is additionally calculated using an expansion in terms of orthogonal operators for three model examples corresponding to different limiting realizations of spin systems. It is shown that the results of the microscopic theory at least qualitatively agree with both the results obtained for model examples and experimental results obtained recently for adamantane.
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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) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : Spin-Fluctuation Renormalization of the Temperature of a Superconducting s-Phase in Rare-Earth Intermetallides
Коллективы :
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 107, Is. 4. - P679-691. - ISSN 1063-7761, DOI 10.1134/S1063776108100166
Примечания : Cited References: 34. - This study was supported in part by the Russian Foundation for Basic Research ( project no. 07-02-00226), the Department of Physic of the Russian Academy of Sciences ( within the program "Strongly Correlated Electrons in Semiconductors, Superconductors, and Magnetic Materials"), and the Siberian Branch of the Russian Academy of Sciences ( integration project no. 3.4).
Предметные рубрики: HEAVY-FERMION SUPERCONDUCTORS
PERIODIC ANDERSON MODEL
WAVE SUPERCONDUCTIVITY
PERTURBATION-THEORY
MECHANISM
VALENCE
SYSTEMS
LATTICE
STATE
Ключевые слова (''Своб.индексиров.''): differential equations--electric conductivity--green's function--numerical analysis--rare earth elements--spin dynamics--spin fluctuations--anomalous components--critical temperatures--experimental datums--infinite systems--numerical calculations--order parameters--periodic anderson models--renormalization--s-phase--skutterudite--strong electron correlations--sub systems--superconducting states--superconductivity
Аннотация: A theory of the superconducting state with s-type symmetry of the order parameter ( the transition to this state was observed in recently discovered heavy-fermion skutterudite LaFe(4)P(12)) is developed using the periodic Anderson model in the limit of strong electron correlations. Exact representations of Green's functions of the superconducting phase via the normal and anomalous components of the mass and strength operators are obtained. It is shown that an important role in the description of this superconducting phase is played by the anomalous components of the strength operator, which reflect spin-fluctuation processes in the localized subsystem. These components are calculated in the one-loop approximation using the solution of an infinite system of integral equations of self-consistency for the superconducting phase. Numerical calculations show that allowance for the process of scattering on spin fluctuations leads to renormalization of the critical temperature and provides agreement with the experimental data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Korovushkin M. M.
Заглавие : Renormalization of Energy Structure and Oscillation Period in the de Haas-van Alphen Effect at the Strong Intersite Coulomb Interaction
Разночтения заглавия :авие SCOPUS: Renormalization of energy structure and oscillation period in the de Haas-van Alphen effect at the strong intersite Coulomb interaction
Место публикации : J. Phys. Soc. Jpn.: PHYSICAL SOC JAPAN, 2011. - Vol. 80, Is. 1. - Ст.14703. - С. P. - ISSN 0031-9015, DOI 10.1143/JPSJ.80.014703
Примечания : Cited References: 36. - This study was supported by the program "Quantum Physics of Condensed Matter'' of the Presidium of the Russian Academy of Sciences (RAS), the Russian Foundation for Basic Research (project No. 10-02-00251), the Federal goal-oriented program Scientific Brainpower of the Russian Innovations 2009-2013, and the Siberian Division of RAS (Interdisciplinary Integration project No. 53). One of the authors (M. K.) would like to acknowledge the support of the Lavrentiev's Competition of the Siberian Division of RAS. The authors are grateful to the Physical Society of Japan for financial support in publication.
Предметные рубрики: T-C SUPERCONDUCTOR
EXTENDED HUBBARD-MODEL
CUPRATE SUPERCONDUCTORS
ELECTRON CORRELATIONS
QUANTUM OSCILLATIONS
FERMI-SURFACE
OXIDES
TEMPERATURE
STATE
BANDS
Ключевые слова (''Своб.индексиров.''): strongly correlated electron systems--cuprate superconductors--intersite coulomb interaction--t-v model--de haas-van alphen effect--cuprate superconductors--de haas-van alphen effect--intersite coulomb interaction--strongly correlated electron systems--t-v model
Аннотация: The effect of strong intersite Coulomb correlations on the formation of the electron structure of the t-V model has been studied. A qualitatively new result indicating the occurrence of a split-off band of Fermi states has been obtained. The spectral intensity of this band increases with an increase in doping level and is determined by the mean-square fluctuation of occupation numbers. This results in the transformation of the energy structure and the integrated density of states and in a further decrease in state occupation in the quasimomentum space near the Fermi level as compared with Hubbard renormalization. It has been shown that this effect leads to an increase in the area of the quasimomentum space part limited by the Fermi contour and is important for the analysis of the de Haas-van Alphen oscillations in cuprate superconductors.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Val'kova T. A., Shklyaev A. A.
Заглавие : Quantum fluctuations in a two-dimensional antiferromagnet with four-spin interaction of cubic symmetry
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 10. - P2061-2066. - ISSN 1063-7834, DOI 10.1134/S1063783411100350
Примечания : Cited References: 13. - This study was supported by the Presidium of the Russian Academy of Sciences (Program "Quantum Physics of Condensed Matter"), the Siberian Branch of the Russian Academy of Sciences (Interdisciplinary Integration project no. 53), the Ministry of Education and Science of the Russian Federation (Russian Federal Targeted Program "Scientific and Scientific-Pedagogical Personnel of the Innovative Russia" in 2009-2013), and the Russian Foundation for Basic Research (project no. 09-02-00127).
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
TEMPERATURE
STATE
Аннотация: The excitation spectrum of a non-Heisenberg 2D antiferromagnet with the four-spin interaction of cubic symmetry has been calculated in the first order of 1/2S. It has been shown that, for weak anisotropy, the N,el state is destroyed by quantum fluctuations. The phase diagrams showing the stability regions of the N,el phase in the space of spin-anisotropy parameters have been plotted.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M., Barabanov A. F.
Заглавие : Origin of the spin polaron quasiparticles and their cooper instability in High-Tc superconductors
Коллективы : Russian Foundation for Basic Research [13-02-00523, 13-02-00909]; Dynasty Foundation
Место публикации : J. Supercond. Nov. Magn.: Springer, 2016. - Vol. 29, Is. 4. - P.1049-1055. - ISSN 1557-1939, DOI 10.1007/s10948-016-3383-8. - ISSN 1557-1947(eISSN)
Примечания : Cited References:15. - This study was supported by the Russian Foundation for Basic Research, projects nos. 13-02-00523, 13-02-00909 and the Dynasty Foundation.
Предметные рубрики: Model
State
Ключевые слова (''Своб.индексиров.''): cuprate high-t-c superconductors--spin polarons--spin-fermion model
Аннотация: IIn the framework of the spin-fermion model, it is shown that accounting for the strong spin-charge fluctuations between holes of copper and oxygen ions in cuprate High-T c superconductors leads to the formation of the Fermi spin-polaron quasiparticles. It is demonstrated that the large value of the binding energy of such quasiparticle is determined by the processes in which hopping intensity of the oxygen holes depends significantly on the spin configuration of holes on the copper and oxygen ions. It was found that the ensemble of such quasiparticles manifests Cooper instability and the concentration dependence of the critical temperature is in good agreement with the experimental data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Aksenov S. V., Ulanov E. A.
Заглавие : Inelastic tunnel transport of electrons through an anisotropic magnetic structure in an external magnetic field
Коллективы : Russian Foundation for Basic Research [13-02-00523, 13-02-98013, 14-02-31280]; Russian Federation [MK-526-526.2013.2, SP-6361.2013.5]
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 119, Is. 1. - P.124-137. - ISSN 1063-7761, DOI 10.1134/S1063776114060065. - ISSN 1090-6509
Примечания : Cited References: 35. - This work was performed under the Program "Quantum Mesoscopic and Disordered Systems" of the Presidium of the Russian Academy of Sciences and supported financially by the Russian Foundation for Basic Research (project nos. 13-02-00523, 13-02-98013, and 14-02-31280). The work of one of coauthors (S. V. A.) was supported by grant no. MK-526-526.2013.2 of the President of the Russian Federation and scholarship SP-6361.2013.5 of the President of the Russian Federation.
Предметные рубрики: SINGLE-MOLECULE
SPECTROSCOPY
ATOM
STATE
Аннотация: Quantum transport of electrons through a magnetic impurity located in an external magnetic field and affected by a substrate is considered using the Keldysh diagram technique for the Fermi and Hubbard operators. It is shown that in a strongly nonequilibrium state induced by multiple reflections of electrons from the impurity, the current-voltage (I-V) characteristic of the system contains segments with a negative conductivity. This effect can be controlled by varying the anisotropy parameter of the impurity center as well as the parameters of coupling between the magnetic impurity and metal contacts. The application of the magnetic field is accompanied by an increase in the number of Coulomb steps in the I-V curve of the impurity. The effect of appreciable magnetoresistance appears in this case. We demonstrate the possibility of switching between magnetic impurity states with different total spin projection values in the regime of asymmetric coupling of this impurity with the contacts.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Aksenov S. V., Ulanov E. A.
Заглавие : Effects of multiple reflection in the process of inelastic electron transport through an anisotropic magnetic atom
Коллективы : Presidium of the Russian Academy of Sciences; Ministry of Education and Science of Russian Federation [16.740.11.0644]; Russian Foundation for Basic Research [12-02-31130, 13-02-00523, 13-02-98013]; Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools [MK-526.2013.2, SP-6361.2013.5]
Место публикации : JETP Letters. - 2013. - Vol. 98, Is. 7. - P.403-409. - ISSN 0021-3640, DOI 10.1134/S0021364013200162
Примечания : Cited References: 27. - This work was supported by the Presidium of the Russian Academy of Sciences (program "Quantum Mesoscopic and Disordered Systems"), the Ministry of Education and Science of Russian Federation (state contract no. 16.740.11.0644, federal program "Human Capital for Science and Education in Innovative Russia" for 2009-2013), and the Russian Foundation for Basic Research (project nos. 12-02-31130, 13-02-00523, and 13-02-98013). S. V. A. is grateful to the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools, project nos. MK-526.2013.2 and SP-6361.2013.5.
Предметные рубрики: QUANTUM
SPECTROSCOPY
STATE
Аннотация: The effect of multiple reflection in the process of electron transport on the current-voltage characteristics of an adsorbed magnetic atom with single-ion anisotropy has been investigated. All orders of the perturbation theory with respect to the parameter of coupling between the contacts and the multilevel impurity have been taken into account by the Keldysh diagram technique with the use of Hubbard operators. It has been shown that the current-voltage characteristics of the system in a strongly nonequilibrium regime contains regions of negative differential conductance. The ways of enhancing this effect are discussed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : Distribution function of Hubbard quasiparticles in two-dimensional systems with inclusion of dynamic processes of spin-fluctuation scattering
Коллективы : Russian Foundation for Basic Research [06-02-16100]
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2009. - Vol. 51, Is. 5. - P877-883. - ISSN 1063-7834, DOI 10.1134/S1063783409050011
Примечания : Cited References: 18. - This study was supported by the Russian Foundation for Basic Research (project no. 06-02-16100) and performed within the framework of the Program of the Branch of General Physics and Astronomy of the Russian Academy of Sciences and the Integration Project of the Siberian Branch of the Russian Academy of Sciences.
Предметные рубрики: STATE
Аннотация: Spin-fluctuation scattering in an ensemble of strongly correlated electrons in CuO(2) planes of high-temperature superconductors is investigated. It is demonstrated that this process significantly modifies the distribution function of Hubbard quasiparticles. The influence of spin-fluctuation scattering mathematically manifests itself in the appearance of the correction to the strength operator in the numerator of the single-fermion Green's function dependent on the Matsubara frequency. This correction differently renormalizes the spectral intensity on different energy scales and determines the dependence of the Migdal discontinuity on the electron concentration in the system.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavryushkin P. N., Popov Z. I., Litasov K. D., Gavryushkin A.
Заглавие : Unbiased crystal structure prediction of NiSi under high pressure
Место публикации : J. Appl. Crystallogr.: Wiley-Blackwell, 2015. - Vol. 48, No. 3. - P.906-908. - ISSN 0021, DOI 10.1107/S1600576715005488. - ISSN 16005767(eISSN)
Примечания : Cited References:29. - We thank the Information Technology Centre of Novosibirsk State University for providing access to the cluster computational resources. The research was financially supported by the Russian Science Foundation (grant No. 14-17-00601) and performed under the program of the Ministry of Education and Science of Russia (project No. 14.B25.31.0032). The work of ZIP is supported by the Leading Science School program (No. NS-2886.2014.2).
Предметные рубрики: AUGMENTED-WAVE METHOD
PHASE-TRANSITIONS
STABILITY
EQUATIONS
STATE
Ключевые слова (''Своб.индексиров.''): earth's core--pressure--ab initio calculations--fesi--nisi--cosi--mnsi--isomorphism
Аннотация: On the basis of an unbiased structure prediction, it is shown that the stable form of NiSi under pressures of 100 and 200 GPa is the Pmmn structure. Furthermore, a new stable phase has been discovered: the deformed tetragonal CsCl-type structure with a = 2.174 Å and c = 2.69 Å at 400 GPa. Specifically, the sequence of high-pressure phase transitions is the following: the Pmmn structure below 213 GPa, the tetragonal CsCl type in the range 213–522 GPa, and cubic CsCl higher than 522 GPa. As the CsCl-type structure is considered as the model structure of the FeSi compound at the conditions of the Earth's core, this result implies restrictions on the Fe–Ni isomorphic miscibility in FeSi.
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