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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Аверьянов, Евгений Михайлович
Заглавие : Молекулярно-оптическая и структурная анизотропия нематической смеси Е7
Место публикации : Жидк. крист. и их практич. использ. - 2019. - Т. 19, № 1. - С. 42-51. - ISSN 1991-3966, DOI 10.18083/LCAppl.2019.1.42; Liq. Cryst. Appl. - ISSN 2499–9644
Примечания : Библиогр.: 20
Предметные рубрики: LIQUID
ORDER
POLARIZABILITY
Ключевые слова (''Своб.индексиров.''): нематические смеси--ориентационный порядок нематических смесей--анизотропия локального поля в нематических смесях--свойства молекул в нематических смесях--нематические смеси, ориентационный порядок нематических смесей, анизотропия локального поля в нематических смесях, свойства молекул в нематических смесях--nematic mixtures--orientational order of nematic mixtures--local-field anisotropy in nematic mixtures--molecular properties in nematic mixtures
Аннотация: Для нематической смеси E7 производных цианобифенила исследована связь показателей преломления nj при поляризациях световой волны вдоль (j = ||) и нормально оптической оси (j = ⊥) с параметрами поляризуемости (компонентами γjα, средним значением γmα = (γ||α + 2γ⊥α)/3, анизотропией δγα = γ||α - γ⊥α) и ориентационным порядком молекул типа α, составляющих смесь. Для смеси введен тензор локального поля с компонентами fj =1+Lj(nj2 – 1). Получена связь компонент тензора Лорентца Lj с компонентами Ljα. Температурные зависимости Lj(Т) для смеси Е7 определены с использованием экспериментальных зависимостей nj(λ,Т) от длины световой волны λ. Подтверждена связь Lj(Ljα). Получена температурная зависимость S(Т) материального параметра порядка смеси. Обнаружено изменение среднего значения γm(Т) = ((γ|| + 2γ⊥)/3 для исследованной смеси за счет изменения S(Т). Показано, что зависимость γm(S) обусловлена противоположными по знаку вкладами от изменения конформации бифенильных остовов молекул и межмолекулярных взаимодействий. Полученные результаты сопоставлены со следствиями использования модельных тензоров fj, известных в литературе для смесей.The relation of the refractive indices nj of the nematic mixture E7 consisting of cyanobiphenyl derivatives for the light-wave polarization along (j = ||) and across (j = ⊥) the optical axis with the polarizability parameters (components γjα, mean value γmα = (γ||α + 2γ⊥α)/3, anisotropy δγα = γ||α - γ⊥α) and orientational order of α-type molecules comprising the mixture was investigated. The local-field tensor with components fj =1+Lj(nj2 – 1) was introduced for the mixture and the relationship between the Lorentz-tensor components Lj and the components Ljα was established. The temperature dependences Lj(Т) for the E7 mixture were obtained using experimental dependences nj(λ,T). The relationship Lj(Ljα) was confirmed. The temperature dependence of the material order parameter S(T) was obtained. The change of the mean value γm(Т) = ((γ|| + 2γ⊥)/3 for the studied mixture due to changing of S(Т) was observed. The dependence γm(S) was shown to be caused by two opposite-sign contributions due to changing conformation of molecular biphenyl cores and intermolecular interactions. The obtained results were compared with the consequences of using model tensors fj, which literature data are known for mixtures.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Eremin I.
Заглавие : Theory of magnetic excitations in iron-based layered superconductors
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2008. - Vol. 78, Is. 14. - Ст.140509. - ISSN 1098-0121, DOI 10.1103/PhysRevB.78.140509
Примечания : Cited References: 31
Предметные рубрики: NEUTRON-SCATTERING
INSTABILITY
STATE
ORDER
MODEL
Аннотация: Based on the effective four-band model we analyze the spin response in the normal and superconducting states of the Fe-pnictide superconductors. While the normal-state spin excitations are dominated by the continuum of the interorbital antiferromagnetic fluctuations and the intraband spin-density wave fluctuations, the unconventional superconductivity yields different feedback. The resonance peak in the form of the well-defined spin exciton occurs only for the interband scattering at the antiferromagnetic momentum Q(AFM) for the s(+/-) (extended s wave) superconducting order parameter and it disappears rapidly for q Q(AFM). The resonance feature is extremely weak for the d(x)(2)-y(2)-wave order parameter due to the specific Fermi-surface topology of these compounds. The essential difference between s(+/-)-wave and d(x)(2)-y(2)-wave symmetries for the magnetic excitations can be used for experimental determination of the superconducting wave-function symmetry.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G.
Заглавие : Temperature dependence of the electronic structure of La2CuO4 in the multielectron LDA+GTB approach
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2015. - Vol. 121, Is. 3. - P.457-464. - ISSN 1063-7761, DOI 10.1134/S1063776115090174
Примечания : Cited References: 38. - The work was supported by the Russian Science Foundation (project no. 14-12-00061)
Предметные рубрики: Copper oxides
Model
Superconductivity
Excitations
Instability
Spectrum
States
Order
Аннотация: The band structure of La2CuO4 in antiferromagnetic and paramagnetic phases is calculated at finite temperatures by the multielectron LDA+GTB method. The temperature dependence of the band spectrum and the spectral weight of Hubbard fermions is caused by a change in the occupation numbers of local multielectron spin-split terms in the antiferromagnetic phase. A decrease in the magnetization of the sublattice with temperature gives rise to new bands near the bottom of the conduction band and the top of the valence band. It is shown that the band gap decreases with increasing temperature, but La2CuO4 remains an insulator in the paramagnetic phase as well. These results are consistent with measurements of the red shift of the absorption edge in La2CuO4 with increasing temperature. © 2015, Pleiades Publishing, Inc.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Janoschek M., Fischer P., Schefer J., Roessli B., Pomjakushin V., Meven M., Petricek V., Petrakovskii G. A., Bezmaternykh L. N.
Заглавие : Single magnetic chirality in the magnetoelectric NdFe3((BO3)-B-11)(4)
Разночтения заглавия :авие SCOPUS: Single magnetic chirality in the magnetoelectric NdFe3( 11BO3 )4
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2010. - Vol. 81, Is. 9. - Ст.94429. - ISSN 1098-0121, DOI 10.1103/PhysRevB.81.094429
Примечания : Cited References: 55
Предметные рубрики: NEUTRON-DIFFRACTION
PHASE-TRANSITIONS
SLOW-NEUTRONS
CRYSTAL
NDFE3(BO3)(4)
EXTINCTION
NUCLEAR
ORDER
MNSI
ANTIFERROMAGNETS
Аннотация: We have performed an extensive study of single crystals of the magnetoelectric NdFe3 ((BO3)-B-11)(4) by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T-N approximate to 30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at T-IC approximate to 13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3((BO3)-B-11)(4) is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedoseev A. D.
Заглавие : Realization conditions and the magnetic field dependence of corner excitations in the topological insulator with superconducting coupling on the triangular lattice
Коллективы : Russian Foundation for Basic Research, Government of Krasnoyarsk Territory [19-02-00348]; Krasnoyarsk Regional Fund of Science [20-42-243005]; "Coulomb interactions in the problem of Majorana modes in low-dimensional systems with nontrivial topology" [19-42-240011]; Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific SchoolsLeading Scientific Schools Program [MK1641.2020.2]
Место публикации : J. Exp. Theor. Phys. - 2021. - Vol. 133, Is. 1. - P.71-76. - ISSN 1063-7761, DOI 10.1134/S1063776121060029. - ISSN 1090-6509(eISSN)
Примечания : Cited References: 38. - This work was supported by the Russian Foundation for Basic Research (project no. 19-02-00348), Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research projects: "Study of edge states in oneand two-dimensional topological superconductors" (no. 20-42-243005), "Coulomb interactions in the problem of Majorana modes in low-dimensional systems with nontrivial topology" (no. 19-42-240011), and Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (Project MK1641.2020.2)
Предметные рубрики: EDGE
STATES
ORDER
Аннотация: The studies of the topological properties of systems have recently been extended due to a new concept of higher-order topological insulators and superconductors. Many models were proposed for two-dimensional systems on a square lattice, where corner excitations can appear; however, the problem of existence of such excitations in superconducting systems with a triangular crystal lattice is still poorly understood. Using a topological insulator in the form of a triangle with a chiral superconducting order parameter as an example, we shows that corner excitations can exist in C3-symmetric systems. In spite of a nontopological character, these excitations have energies inside the gap of the first-order edge excitation spectrum over a wide parameter range and are well localized at the corners of the system. Gapless corner excitations are shown to exist in the system at certain parameters. The application of a magnetic field in the system plane removes the triple degeneracy of the corner excitation energy and makes it possible to control the position of the minimum-energy corner excitation using a magnetic field. At the same time the fine adjustment to achieve the gapless excitations at the chosen corner can be made with changing of the magnetic field value.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo investigation of the 2D Heisenberg model with S=1/2
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 1999. - Vol. 41, Is. 1. - P103-107. - ISSN 1063-7834, DOI 10.1134/1.1130737
Примечания : Cited References: 33
Предметные рубрики: SQUARE-LATTICE
GROUND-STATE
SPIN-CORRELATIONS
ANTIFERROMAGNET
LA2CUO4
EU2CUO4
ENERGY
ORDER
Аннотация: The two-dimensional (2D) Heisenberg model with anisotropic exchange (Delta=1-J(x)/J(z)) and S=1/2 is investigated by the quantum Monte Carlo method. The energy, susceptibility, specific heat, spin-spin correlation functions, and correlation radius are calculated. The sublattice magnetization (sigma) and the Neel temperature of the anisotropic antiferromagnet are logarithmic functions of the exchange anisotropy: 1/sigma + 1 + 0.13(1) ln(1/Delta). Crossover of the static magnetic structural factor as a function of temperature from power-law to exponential occurs for T(c)/J approximate to 0.4. The correlation radius can be approximated by 1/xi =2.05T(1.0(6))/exp(1.0(4)/ T). For La(2)CuO(4) the sublattice magnetization is calculated as sigma=0.45, the exchange is J=(1125=1305) K; for Er(2)CuO(4)J similar to 625 K and the exchange anisotropy Delta similar to 0.003. The temperature dependence of the static structural magnetic factor and the correlation radius above the Neel temperature in these compounds can be explained by the formation of topological excitations (spinons). (C) 1999 American Institute of Physics. [S1063-7834(99)02401-6].
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Flerov I. N., Tressaud A., Molokeev M. S., Kartashev A. V., Pogoreltsev E. I., Bayukov O. A.
Заглавие : Phase transitions in fluoride KFe2F6 with tetragonal tungsten bronze structure
Коллективы : RFBR [12-02-00056]; Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation [NSh-924.2014.2]
Место публикации : J. Fluor. Chem.: Elsevier Science, 2014. - Vol. 168. - P.204-211. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.09.031. - ISSN 1873-3328
Примечания : Cited References: 14. - This work was supported by RFBR, project no. 12-02-00056, and the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (grant NSh-924.2014.2).
Предметные рубрики: K3FE5F15
490-K
ORDER
Ключевые слова (''Своб.индексиров.''): tetragonal tungsten bronze structure--phase transition--charge ordering--thermal properties
Аннотация: Heat capacity, thermal dilatation, structure, Mossbauer spectra and dielectric permittivity of fluoride KFe2F6 with tetragonal tungsten bronze crystal structure were studied. The as-made sample undergoes two structural phase transitions P4/mbm (T-1 approximate to 340 K) - Pbam (T-2 approximate to 250 K) - G(2) and magnetic phase transformation at T-m approximate to 133 K. Heating up to 600-700 K and subsequent cooling in helium atmosphere leads to a change of phase transition temperatures and diffused anomalies in thermal expansion. The results obtained and influence of thermal prehistory of the sample on its physical properties are discussed in the context of previous studies on related fluorides KFe2F6, which sometimes suggest conflicting structural details. (C) 2014 Elsevier B.V. All rights reserved.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : GOREV M. V., FLEROV I. N., VORONOV V. N., MISYUL S. V.
Заглавие : P = T-PHASE DIAGRAMS OF ELPASOLITES RB2KB3+F6(B3+ = HO,DY,TB)
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1993. - Vol. 35, Is. 4. - P1022-1027. - ISSN 0367-3294
Примечания : Cited References: 16
Предметные рубрики: RIGID SPHERE MODEL
RB2KMIIIF6 ELPASOLITES
TRANSITIONS
ORDER
WOS
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krakhalev M. N.
Заглавие : Oblique light incidence method to study topological defects in nematic layers with conical boundary conditions
Место публикации : Sci. Rep. - 2021. - Vol. 11, Is. 1. - Ст.17433. - ISSN 2045-2322, DOI 10.1038/s41598-021-96784-9
Примечания : Cited References: 54
Предметные рубрики: CHOLESTERIC FINGERS
DISCLINATIONS
SURFACE
WALLS
ORDER
Аннотация: A polarization microscopy method to investigate the orientational structures and boojums formed in the chiral and achiral nematic layers under conical (tilted) boundary conditions has been developed. Oblique light incidence on nematic layer is used, due to which the phase difference between the ordinary and extraordinary waves depends on the director’s azimuthal angle. The phase difference gets maximal when the director azimuthal angle of achiral nematic φ(x,y)=0 and an azimuthal angle at the center of the chiral nematic layer φ0(x,y)=0 independently of the total twist angle φTOTAL. It has been found that the m=+1 boojums with the phase ξ=±90° and ξ=(−90°+φTOTAL/2) are formed in achiral and chiral nematics, respectively, at the director tilt angle θd/2≅40° at the interface. In addition, the defectless structure of chiral nematic with the periodically variable azimuthal director angle on the substrates has been studied.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aver'yanov E. M.
Заглавие : Nonlinear coupling between the mean polarizability (gamma)over-bar of molecules and the local-field anisotropy in a liquid crystal and change of the "(gamma)over-bar = const" paradigm
Разночтения заглавия :авие SCOPUS: Nonlinear coupling between the mean polarizability gamma ̄ of molecules and the local-field anisotropy in a liquid crystal and change of the "gammā = const" paradigm; авие SCOPUS: Nonlinear coupling between the mean polarizability gamma ? of molecules and the local-field anisotropy in a liquid crystal and change of the "gamma = const" paradigm
Место публикации : JETP Letters. - 2008. - Vol. 87, Is. 5. - P.258-261. - ISSN 0021-3640, DOI 10.1134/S002136400805007X; \b JETP Letters. - 2008. - Vol. 87, Is. 5. - P.258-261. - Вариант Sopus
Примечания : Cited References: 14
Предметные рубрики: REFRACTIVE-INDEXES
ORDER
Аннотация: The nonlinear relation between the mean effective polarizability (gamma) over bar of molecules and the local-field anisotropy in uniaxial liquid crystals is demonstrated. Stringent constraints on (gamma) over bar from below, indicative of the dependence of on the liquid-crystal state and the change of the "(gamma) over bar = const" paradigm, are established. The theoretical results are confirmed by experiments with nematic liquid crystals having high and low birefringences.
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