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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Korshunov M. M., Nikolaev S., Shneyder E. I., Krinitsyn A.
Заглавие : Normal and superconducting properties of cuprates in multielectron theory
Место публикации : J. Supercond. Nov. Magn. - 2013. - Vol. 26, Is. 9. - P.2831-2835. - ISSN 1557-1939, DOI 10.1007/s10948-013-2263-8
Ключевые слова (''Своб.индексиров.''): cluster perturbation theory--fermi surface reconstruction--strong electron correlations
Аннотация: We consider the doping dependence of the normal and superconducting properties of La2-x Srx CuO4 in the low energy effective model based on the ab initio LDA+GTB calculations. We have found that two quantum phase transitions (QPT) of the Lifshitz type correspond well to the experimental phase diagram. For superconducting state, we have considered both magnetic and phonon mechanisms of pairing. Finally, we compare the true Fermi surface and the spectral intensity map seen in ARPES within a new norm conserving cluster perturbation theory (NC-CPT). В© 2013 Springer Science+Business Media New York.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Makarov I. A., Shneyder E. I., Togushova Yu. N., Korshunov M. M., Gavrichkov V. A.
Заглавие : Magnetic mechanisms of pairing in strongly correlated electron system of copper oxides
Место публикации : Recent advances in superconductivity research. - New York: Nova Science Publishers, 2013. - Chapter 6. - P.93-143. - ISBN 978-1-62618-406-0
Ключевые слова (''Своб.индексиров.''): strong electronic correlations--magnetic mechanism of pairing--quantum phase transitions--electronic structure--hubbard operators--cuprates
Аннотация: The multielectron LDA+GTB approach has been developed to calculate electronic structure of strongly correlated cuprates. At low energies the effective Hamiltonian of the t- t’- t”- t﬩-J*-J﬩ -model has been derived with parameters coming from the ab initio calculation for LSCO. The electronic structure of LSCO has been calculated self-consistently with the short-range antiferromagnetic order for various doping level. Two Lifshitz-type quantum phase transitions with Fermi surface topology changes have been found at dopings x(c1) = 0.15 and x(c2) = 0.24. Its effect on normal and superconducting properties has been calculated. The interatomic ex change parameter and its pressure dependence has been calculated within LDA+GTB scheme. The magnetic mechanisms of d-wave pairing induced by static and dynamical spin correlations are discussed. Simultaneous treatment of magnetic and phonon pairing results in the conclusion that both contributions are of the same order. For two layer cuprates like YBCO the interlayer hopping and exchange effects on the electronic structure and doping dependence of Tc is discussed as well as the Coulomb interaction induced mechanism of pairing.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E.
Заглавие : Quantum and classical correlations in high temperature dynamics of two coupled large spins : conference paper
Коллективы : International Conference on Micro- and Nano-Electronics (Oct. 1-5, 2012; Zvenigorod, Russia)
Место публикации : Proc. SPIE. - 2012. - Vol.8700. - Ст.87001D. - P. - ISSN 0277-786X, DOI 10.1117/12.2016982. - ISSN 978-081949487-0
Примечания : Cited References: 17
Ключевые слова (''Своб.индексиров.''): dynamical correlations--measurement--mutual information--nuclear magnetic resonance--spin coherent states
Аннотация: We study dynamical correlations of two coupled large spins depending on the time and on the spin quantum numbers. In the high-temperature approximation, we obtain analytical expressions for the mutual informations, quantum and classical parts of correlations. The latter was obtained performing the non-orthogonal projective (POVM) measurements onto the spin coherent states of two spins or one spin, as well as by means of the orthogonal projective measurement of von Neumann. Contribution from quantum correlations is much less than that from classical ones and decreasing with the increase in spin quantum numbers at short times. However, it is not so in a time equal to half of the quantum period. © 2012 SPIE.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Зобов, Владимир Евгеньевич
Заглавие : Квантовые и классические корреляции в высокотемпературной динамике двух связанных больших спинов
Место публикации : Теор. и мат. физика. - 2013. - Т. 177, № 1. - С. 111–125. - DOI 1010.4231/tmf8510
Аннотация: Исследуются динамические корреляции двух связанных спинов в зависимости от времени и величин спиновых квантовых чисел. В высокотемпературном приближении получены аналитические выражения для взаимной информации, квантовой и классической частей корреляций. Наряду с ортогональными измерениями рассмотрены неортогональные измерения с базисом из спиновых когерентных состояний. Показано, что на малых временах при увеличении спиновых квантовых чисел квантовая часть корреляций становится много меньше классической части, тогда как на временах, равных половине квантового периода, это не так.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E.
Заглавие : Quantum and classical correlations in high-temperature dynamics of two coupled large spins
Место публикации : THEOR. MATH. PHYS. - 2013. - Vol. 177, Is. 1. - P.1377-1389. - ISSN 0040-5779, DOI 10.1007/s11232-013-0110-5
Ключевые слова (''Своб.индексиров.''): generalized measurement--high-temperature approximation--mutual information--quantum correlation--spin coherent state--spin dynamics
Аннотация: We study the dynamical correlations between two coupled spins depending on time and the value of the spin quantum numbers. In the high-temperature approximation, we obtain analytic expressions for the mutual information and the quantum and classical parts of correlations. We consider both orthogonal and nonorthogonal measurements in the basis of spin coherent states. We show that at small times, the quantum part of correlations becomes much less than the classical part as the spin quantum numbers increase, while the situation is quite different at times equal to half the quantum period.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Komogortsev S. V., Iskhakov R. S., Sheftel E. N., Harin E. V., Krikunov A. I., Eremeeva E. V.
Заглавие : Magnetization correlations and random magnetic anisotropy in nanocrystalline films Fe 78Zr 10N 12
Коллективы : Moscow International Symposium on Magnetism
Место публикации : Diffusion and Defect Data Pt.B: Solid State Phenomena. - 2012. - Vol. 190. - P.486-489. - ISBN 9783037854365, DOI 10.4028/www.scientific.net/SSP.190.486
Ключевые слова (''Своб.индексиров.''): magnetic correlations--magnetic force microscopy--nanocrystalline alloys--random magnetic anisotropy--ferromagnetic correlations--magnetic correlation--nanocrystalline films--random magnetic anisotropies--magnetic force microscopy--magnetic materials--nanocrystalline alloys--zirconium--magnetism
Аннотация: The quantitative analysis of static ferromagnetic correlations in nanocrystalline films Fe 78Zr 10N 12 was performed by two methods: the correlation magnetometry technique and magnetic force microscopy. The data, obtained by both methods, prove to be in good agreement. В© (2012) Trans Tech Publications.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Zobov V. E.
Заглавие : Quantum and classical correlations in high temperature dynamics of two coupled large spins
Коллективы : "Micro- and nanoelectronics – 2012", Int. Conf. (2012 ; окт. ; 1-5; Москва/ Звенигород, Россия)
Место публикации : International Conference "Micro- and Nanoelectronics – 2012": Book of abstracts. - 2012. - Ст.q1-02. - P.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G., Shneider E. I.
Заглавие : Dependence of the critical temperature of high-temperature cuprate superconductors on hoppings and spin correlations between CuO2 planes
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 114, Is. 2. - P.329-342. - ISSN 1063-7761, DOI 10.1134/S1063776112020264
Примечания : Cited References: 73. - This study was supported in part by the Presidium of the Russian Academy of Sciences (program "Quantum Physics of Condensed Media," project no. 18.7), jointly by the Siberian and Ural branches of the Russian Academy of Sciences (integration projects project no. 40), the Russian Foundation for Basic Research (project no. 09-02-00127), the Presidential Program in Support of Young Scientists in Russia (project no. MK-1683.2010.2), and the federal target program "Specialists" (project no. P891). One of the authors (E.I.Sh.) gratefully acknowledges support from the nonprofit Dynasty foundation.
Предметные рубрики: T-J MODEL
BAND HUBBARD-MODEL
SINGLE-CRYSTALS
TRANSITION-TEMPERATURE
FERMI-SURFACE
DOPING DEPENDENCE
THERMAL-EXPANSION
COPPER OXIDES
ANISOTROPY
LA2-XSRXCUO4
Аннотация: The influence of interlayer hoppings on the superconducting transition temperature (T c) in bilayer cuprates has been studied. The parameter of hopping between layers is expressed as t ⊥(k) = t ⊥(cos(k x ) − cos(k y ))2 and treated as a small perturbation for the states of two CuO2 planes described by the t-t′-t″-J* model. In the generalized mean field approximation for dx2−y2{d_{{x. } - {y. }}} symmetry of the superconducting gap, neither the interlayer hopping or exchange interaction, nor the pair hopping between CuO2 layers provides an additional mechanism of Cooper pair formation or an increase in T c. In the concentration dependence of T c, the bilayer splitting of the upper Hubbard band of quasi-holes is manifested as two peaks with temperatures slightly lower than the maximum T c for a single-layer cuprate. Interlayer antiferromagnetic spin correlations suppress bilayer splitting.
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10.

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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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Korovushkin M. M.
Заглавие : Lower subband splitting and superconductivity of 2D Hubbard fermions with strong intersite correlations
Коллективы : International Symposium "Nanophysics and Nanoelectronics-2011" (March 2011; Nizhni Novgorod)
Место публикации : Bull. Russ. Acad. Sci. Phys.: Allerton Press, 2012. - Vol. 76, Is. 2. - P.133-135. - ISSN 1062-8738, DOI 10.3103/S1062873812020074
Примечания : Cited References: 6. - This study was supported by Quantum Physics of Condensed Matter program of the Presidium of the Russian Academy of Sciences; the Russian Foundation for Basic Research, project np. 10-02-00251; the federal target program Scientists and Science Teachers of an Innovate Russia, 2009-2013; the Siberian Branch of the Russian Academy of Sciences, complex integration project no. 53; RF Presidential Grant MK-1300.2011.2; and the Siberian Branch of the Russian Academy of Sciences' Lavrent'ev Competition for Young Scientists.
Ключевые слова (''Своб.индексиров.''): coulomb correlations--doping levels--electron structures--fermi state--hubbard--intersite correlation--mean-square fluctuations--spectral intensity--split-off band--subbands--natural sciences
Аннотация: The effect of the strong intersite Coulomb correlations on the formation of an electron structure in the Shubin-Vonsowsky model in the regime of strong one-site correlations is studied. The results reveal a split-off band of the Fermi states. The spectral intensity of this band grows with the enhancement of the doping level and is determined by the mean-square fluctuation of occupation numbers. This changes the structure of the electron density of states qualitatively. © 2012 Allerton Press, Inc.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kagan M. Y., Val'kov V. V., Mitskan V. A., Korovushkin M. M.
Заглавие : The Kohn-Luttinger effect and anomalous pairing in new superconducting systems and graphene
Коллективы : Physics Department of the Russian Academy of Sciences [P.3.1]; Russian Foundation for Basic Research [14-02-00058, 14-02-31237]; Russian Federation [MK-526.2013.2]; Dynasty Foundation
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 118, Is. 6. - P.995-1011. - ISSN 1063-7761, DOI 10.1134/S1063776114060132. - ISSN 1090-6509
Примечания : Cited References: 114. - This study was supported by the Program of the Physics Department of the Russian Academy of Sciences (project no. P.3.1) and the Russian Foundation for Basic Research (project nos. 14-02-00058 and 14-02-31237). The work of two coauthors (M. M. K. and V.A.M) was supported financially by grant no. MK-526.2013.2 of the President of the Russian Federation and the Dynasty Foundation.
Предметные рубрики: P-WAVE SUPERCONDUCTIVITY
EXTENDED HUBBARD-MODEL
NARROW ENERGY-BANDS
2D KONDO-LATTICE
FERMI GAS
REPULSIVE INTERACTIONS
ELECTRON CORRELATIONS
COOPER INSTABILITY
PHASE-DIAGRAM
SPECTRUM
Аннотация: We present a review of theoretical investigations into the Kohn-Luttinger nonphonon superconductivity mechanism in various 3D and 2D repulsive electron systems described by the Fermi-gas, Hubbard, and Shubin-Vonsovsky models. Phase diagrams of the superconducting state are considered, including regions of anomalous s-, p-, and d-wave pairing. The possibility of a strong increase in the superconducting transition temperature T c even for a low electron density is demonstrated by analyzing the spin-polarized case or the two-band situation. The Kohn-Luttinger theory explains or predicts superconductivity in various materials such as heterostructures and semimetals, superlattices and dichalcogenides, high-T c superconductors and heavy-fermion systems, layered organic superconductors, and ultracold Fermi gases in magnetic traps. This theory also describes the anomalous electron transport and peculiar polaron effects in the normal state of these systems. The theory can be useful for explaining the origin of superconductivity and orbital currents (chiral anomaly) in systems with the Dirac spectrum of electrons, including superfluid 3He-A, doped graphene, and topological superconductors.
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13.

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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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Quantum and classical correlations in the solid-state NMR free induction decay
Место публикации : Appl. Magn. Reson.: Springer, 2014. - Vol. 45, Is. 11. - P.1169-1177. - ISSN 0937-9347, DOI 10.1007/s00723-014-0562-2. - ISSN 1613-7507
Примечания : Cited References: 16
Предметные рубрики: LATTICE
SPINS
Аннотация: The free induction decay (FID) of the transverse magnetization in a dipolar-coupled rigid lattice is a fundamental problem in magnetic resonance and in the theory of many-body systems. As it was shown earlier the FID shapes for the systems of classical magnetic moments and for quantum nuclear spin ones coincide if there are many nearly equivalent nearest neighbors n in a solid lattice. In this paper, we reduce a multispin density matrix of above system to a two-spin matrix. Then we obtain analytic expressions for the mutual information and the quantum and classical parts of correlations at the arbitrary spin quantum number S, in the high-temperature approximation. The time dependence of these functions is expressed via the derivative of the FID shape. To extract classical correlations for S 1/2 we provide generalized POVM measurement (positive-operator-valued measure) using the basis of spin coherent states. We show that in every pair of spins the portion of quantum correlations changes from 1/2 to 1/(S + 1) when S is growing up, and quantum properties disappear completely only if S → ∞.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Iskhakov R. S., Komogortsev S. V., Balaev A. D., Gavriliuk A. A.
Заглавие : The manifestations of the two-dimensional magnetic correlations in the nanocrystalline ribbons Fe64CO21B15
Место публикации : J. Magn. Magn. Mater.: Elsevier Science, 2015. - Vol. 374. - P.423-426. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2014.08.078. - ISSN 1873-4766
Примечания : Cited References: 42
Предметные рубрики: GRAIN-SIZE DEPENDENCE
RANDOM ANISOTROPY
AMORPHOUS-ALLOYS
COERCIVE FORCE
FERROMAGNETS
FILMS
SATURATION
Fe
MICROSTRUCTURE
EVOLUTION
Ключевые слова (''Своб.индексиров.''): magnetic correlations--nanoclystalline alloys--random magnetic anisotropy--coercivity
Аннотация: We report and discuss the grain size dependence of the coercivity and approach magnetization to saturation in the FeCoB ribbons. Instead of expected three-dimensional magnetic correlations for 20 mu m thick ribbon with grain size about 10 nm, the observed behavior could be attributed to the two-dimensional stochastic magnetic domains and two dimensional magnetization ripple. (C) 2014 Elsevier B.V. All rights reserved.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M., Barabanov A. F.
Заглавие : d-Wave pairing in an ensemble of spin polaron quasiparticles in the spin-fermion model of the electronic structure of the CuO2 plane
Коллективы : Dynasty Foundation, Russian Foundation for Basic Research (Siberia) [13-02-00523,13-02-00909, 13-02-98013]
Место публикации : Phys. Lett. A: Elsevier Science, 2015. - Vol. 379, Is. 5. - P.421-426. - ISSN 0375, DOI 10.1016/j.physleta.2014.11.036. - ISSN 18732429(eISSN)
Примечания : Cited References:26. - This study was supported by the Russian Foundation for Basic Research,projects Nos. 13-02-00523, 13-02-00909 and 13-02-98013 (Siberia) and theDynasty Foundation.
Предметные рубрики: SUPERCONDUCTIVITY
ANTIFERROMAGNETISM
Ключевые слова (''Своб.индексиров.''): hight-temperature cuprate superconductors--tree-band p-d model--spin--polaron--strong electron correlations
Аннотация: It is demonstrated for the first time that the strong coupling between spin moments of copper ions and oxygen holes, which arises upon hybridization mixing of two hole subsystems in the Emery model, not only affects the formation of spin polaron quasiparticles but also ensures effective attraction between them via the exchange interaction. This results in the Cooper instability with d-wave pairing in a 2D ensemble of spin polaron quasiparticles. The T-x phase diagram obtained using this approach agrees well with the available experimental data. (C) 2014 Elsevier B.V. All rights reserved.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E.
Заглавие : Quantum and classical correlations in electron-nuclear spin echo
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 119, Is. 5. - P.817-827. - ISSN 1063-7761, DOI 10.1134/S1063776114110132. - ISSN 1090-6509
Примечания : Cited References: 38
Предметные рубрики: DISCORD
QUBITS
Аннотация: The quantum properties of dynamic correlations in a system of an electron spin surrounded by nuclear spins under the conditions of free induction decay and electron spin echo have been studied. Analytical results for the time evolution of mutual information, classical part of correlations, and quantum part characterized by quantum discord have been obtained within the central-spin model in the high-temperature approximation. The same formulas describe discord in both free induction decay and spin echo although the time and magnetic field dependences are different because of difference in the parameters entering into the formulas. Changes in discord in the presence of the nuclear polarization β I in addition to the electron polarization β S have been calculated. It has been shown that the method of reduction of the density matrix to a two-spin electron-nuclear system provides a qualitatively correct description of pair correlations playing the main role at β S ≈ β I and small times. At large times, such correlations decay and multispin correlations ensuring nonzero mutual information and zero quantum discord become dominant.
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18.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Quantum and classical correlations in the solid-state NMR free induction decay
Место публикации : International Conference Magnetic Resonance: Fundamental Research and Pioneering Applications: Book of abstracts. - 2014. - Ст.P 77. - P.160
Примечания : Cited References: 16
Аннотация: The free induction decay (FID) of the transverse magnetization in a dipolar-coupled rigid lattice is a fundamental problem in magnetic resonance and in the theory of many-body systems. As it was shown earlier the FID shapes for the systems of classical magnetic moments and for quantum nuclear spin ones coincide if there are many nearly equivalent nearest neighbors n in a solid lattice. In this paper, we reduce a multispin density matrix of above system to a two-spin matrix. Then we obtain analytic expressions for the mutual information and the quantum and classical parts of correlations at the arbitrary spin quantum number S, in the high-temperature approximation. The time dependence of these functions is expressed via the derivative of the FID shape. To extract classical correlations for S 1/2 we provide generalized POVM measurement (positive-operator-valued measure) using the basis of spin coherent states. We show that in every pair of spins the portion of quantum correlations changes from 1/2 to 1/(S + 1) when S is growing up, and quantum properties disappear completely only if S → ∞.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhang H., Yu T., Chen Z., Nelson C. S., Bezmaternykh L. N., Abeykoon A. M. M., Tyson T. A.
Заглавие : Probing magnetostructural correlations in multiferroic HoAl3(BO3)4
Место публикации : Phys. Rev. B: American Physical Society, 2015. - Vol. 92, Is. 10. - Ст.104108. - ISSN 1098, DOI 10.1103/PhysRevB.92.104108. - ISSN 1550235X(eISSN)
Примечания : Cited References:97. - This work is supported by the U.S.Department of Energy Grant No. DE-FG02-07ER46402. Synchrotron powder x-ray diffraction and x-ray absorption data acquisition were performed at Brookhaven National Laboratory's National Synchrotron Light Source (NSLS). Use of the NSLS was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886. The Physical Properties Measurement System used in the heat capacity measurements was acquired under National Science Foundation Major Research Instrumentation Grant No. DMR-0923032 (American Recovery and Reinvestment Act award). This research used resources of the National Energy Research Scientific Computing Center, a U.S. Department of Energy Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Предметные рубрики: PAIR DISTRIBUTION FUNCTION
TOTAL-ENERGY CALCULATIONS
WAVE BASIS-SET
FERROELECTRIC POLARIZATION
DEBYE TEMPERATURES
SINGLE-CRYSTALS
HOFE3(BO3)4
GDFE3(BO3)4
DIFFRACTION
FEATURES
Аннотация: The system HoAl3(BO3)(4) has recently been found to exhibit a large magnetoelectric effect. To understand the mechanism, macroscopic and atomic level properties of HoAl3(BO3)(4) were explored by temperature and magnetic field dependent heat capacity measurements, pressure and temperature dependent x-ray diffraction measurements, as well as temperature and magnetic field dependent x-ray absorption fine structure measurements. The experimental work was complemented by density functional theory calculations. An anomalous change in the structure is found in the temperature range where large magnetoelectric effects occur. No significant structural change or distortion of the HoO6 polyhedra is seen to occur with magnetic field. However, the magnetic field dependent structural measurements reveal enhanced correlation between neighboring HoO6 polyhedra. This observed response is seen to saturate near 3 T. A qualitative atomic level description of the mechanism behind the large electric polarization induced by magnetic fields in the general class of RAl3(BO3)(4) systems (R = rare earth) is developed.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sandalov I. S., Zamkova N. G., Zhandun V. S., Tarasov I. A., Varnakov S. N., Yakovlev I. A., Solovyov L. A., Ovchinnikov S. G.
Заглавие : Effect of electron correlations on the Fe3Si and α- FeSi2 band structure and optical properties
Коллективы : Russian Fund of Basic Research [14002-00186, 13-02-01265]; President of Russia Grants [2886.2014.2, 924.2014.2]
Место публикации : Phys. Rev. B: American Physical Society, 2015. - Vol. 92, Is. 20. - Ст.205129. - ISSN 1098-0121, DOI 10.1103/PhysRevB.92.205129. - ISSN 1550-235X(eISSN)
Примечания : Cited References:69. - The theoretical part of this work was supported by Russian Fund of Basic Research, Grant No. 14002-00186 and the President of Russia Grants No. 2886.2014.2 and No. 924.2014.2 for support of Leading Scientific School. The calculations were performed with the computer resources of NRC "Kurchatov Institute" (ui2.computing.kiae.ru). The experimental work was supported by Russian Fund of Basic Research, Grant No. 13-02-01265. I.S. thanks A. Ruban for useful discussion.
Предметные рубрики: DENSITY-FUNCTIONAL THEORY
TOTAL-ENERGY CALCULATIONS
AUGMENTED-WAVE METHOD
BASIS-SET
METALS
ABSORPTION
EMISSION
SURFACES
ALLOYS
LAYERS
Аннотация: We use the Vienna ab initio simulation package (vasp) for evaluation of the quasiparticle spectra and their spectral weights within Hedin's GW approximation (GWA) for Fe3Si and α-FeSi2 within the non-self-consistent one-shot approximation G0W0 and self-consistent scGWA with the vertex corrections in the particle-hole channel, taken in the form of two-point kernel. As input for G0W0, the band structure and wave functions evaluated within the generalized gradient corrected local-density approximation to density functional theory (GGA) have been used. The spectral weights of quasiparticles in these compounds deviate from unity everywhere and show nonmonotonic behavior in those parts of bands where the delocalized states contribute to their formation. The G0W0 and scGWA spectral weights are the same within 2%–5%. The scGWA shows a general tendency to return G0W0 bands to their GGA positions for the delocalized states, while in the flat bands it flattens even more. Variable angle spectroscopic ellipsometry measurements at T=296 K on grown single-crystalline ∼50-nm-thick films of Fe3Si on n-Si(111) wafer have been performed in the interval of energies ω∼(1.3–5) eV. The comparison of G0W0 and scGW theory with experimental real and imaginary parts of permittivity, refractive index, extinction and absorption coefficients, reflectivity, and electron energy loss function shows that both G0W0 and scGW qualitatively describe experiment correctly, the position of the low-energy peaks is described better by the scGW theory, however, its detailed structure is not observed in the experimental curves. We suggest that the angle-resolved photoemission spectroscopy experiments, which can reveal the fine details of the quasiparticle band structure and spectral weights, could help to understand (i) if the scGWA with this type of vertex correction is sufficiently good for description of these iron silicides and, possibly, (ii) why some features of calculated permittivity are not seen in optical experiments.
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