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Вид документа : Однотомное издание
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Makarov I. A., Shneyder E. I., Togushova Yu.N., Gavrichkov V. A., Korshunov M. M.
Заглавие : Magnetic mechanisms of pairing in strongly correlated electron system of copper oxides [Electronic resource]
Место публикации : arXiv. - 2015. - Ст.eprint arXiv:1510.08640
Примечания : Cited References: 214. - The authors acknowledge support from FCP Scientific and Research-and-Educational Personnel of Innovative Russia for 2009-2013 (GK 16.740.12.0731 and GK 16.740.11.0740), RFBR (Grants 12-02-31534 and 12-02-31597), Siberian Federal University (Theme #F-11), Governmental support of leading scientific schools of Russia (NSh-1044.2012.2), Program of SB RAS #44, Presidium of RAS program #20.7. EIS, IAM, and MMK are grateful to The Dynasty Foundation and ICFPM forthe financial supportIn book.: Recent advances in superconductivity research", ed. by C.B. Taylor, 321 p., Nova Science Publishers Inc. New York, 2013 ISBN: 978-1-62618-406-0, Chapter 6
Предметные рубрики: Condensed matter-- Strongly correlated electrons
Superconductivity
Ключевые слова (''Своб.индексиров.''): strong electronic correlations--cuprates--hubbard operators--electronic structure--quantum phase transitions--magnetic mechanism of pairing
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 xc1=0.15 and xc2=0.24. Its effect on normal and superconducting properties has been calculated. The interatomic exchange 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 : Однотомное издание
Шифр издания :
Заглавие : Euro-asian symposium "Trends in magnetism" (EASTMAG-2004) : Abstract book
Выходные данные : Krasnoyarsk, 2004
Колич.характеристики :418 с
Коллективы : Российская академия наук, Сибирское отделение РАН, Институт физики им. Л.В. Киренского Сибирского отделения РАН, Красноярский государственный университет, Красноярский государственный технический университет, Институт физики металлов Уральского отделения РАН, Научный совет по физике конденсированных сред РАН, Научный совет РАН по физике низких температур, Красноярский научный центр Сибирского отделения РАН, Euro-asian symposium "Trends in magnetism" (2; 2004 ; Aug. 24-27; Krasnoyarsk), "Trends in magnetism", Euro-Asian Symposium (2; 2004 ; Aug. 24-27; Krasnoyarsk)
Примечания : Bibliogr. at the end of the articles - Auth. ind. :
Содержание : Fundamental magnetic properties ; Transport phenomena and spin electronics ; Magnetism and strongly correleted electron systems ; Spin glasses, disordered magnetic systems ; Dynamics of spin systems and magnetic resonances ; Magnetooptics and X-ray magnetooptics ; Magnetic mechanism of the superconductivity ; Domain structure and magnetization processes ; Thin magnetic films and multilayers ; Magnetic particles and nanocrystalline materials ; Molecular magnetism ; Magnetic storage/memory and applications
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bykov A. A., Terent'ev K. Yu., Gokhfeld D. M., Savitskaya N. E., Popkov S. I., Petrov M. I.
Заглавие : Superconductivity on interfaces of nonsuperconducting granules La2CuO4 and La1.56Sr0.44CuO4
Место публикации : J. Supercond. Nov. Magn. - 2018. - Vol. 31, Is. 12. - P.3867–3874. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-018-4668-x
Примечания : Cited References: 19. - The authors are grateful to D.A. Balaev for fruitful discussions, and I.V. Nemtsev for electronic microscope measurements in the center for shared use, KSC SB RAS. The work is supported by the Russian Science Foundation (project No. 17-72-10067).
Ключевые слова (''Своб.индексиров.''): magnetic properties--superconductivity--oxide superconductors--grain boundaries--lco--lsco--josephson media
Аннотация: Composite materials fabricated by annealing of nonsuperconducting ceramics La2CuO4 and La1.56Sr0.44CuO4 at 910 °C during various time are investigated. Areas of superconducting La1.85Sr0.15CuO4 phase arises at boundaries of contacting nonsuperconducting granules. The volume fraction of the superconducting phase increases with increasing annealing time. A model describing the magnetic and transport properties of the samples at low magnetic fields is constructed. The magnetotransport characteristics of obtained samples at low magnetic fields (∼ 100 Oe) are defined by weak links network formed by superconducting areas. At high fields, behavior of the system is defined by a magnetization of the disconnected superconducting islands. The average size of the superconducting areas has been estimated from an extended critical state model.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Semenov S. V., Balaev D. A.
Заглавие : Temperature behavior of the magnetoresistance hysteresis in a granular high-temperature superconductor: Magnetic flux compression in the intergrain medium
Место публикации : Physica C. - 2018. - Vol. 550. - P.19-26. - ISSN 09214534 (ISSN), DOI 10.1016/j.physc.2018.04.005
Примечания : Cited References: 56. - The work was supported by the Russian Science Foundation (Grant No. 17-72-10050 ).
Ключевые слова (''Своб.индексиров.''): barium compounds--copper compounds--grain boundaries--hysteresis--magnetic flux--magnetic moments--magnetization--magnetoresistance--yttrium barium copper oxides
Аннотация: Granular high-temperature superconductors (HTSs) are characterized by the hysteretic behavior of magnetoresistance. This phenomenon is attributed to the effective field in the intergrain medium of a granular HTS. At the grain boundaries, which are, in fact, weak Josephson couplings, the dissipation is observed. The effective field in the intergrain medium is a superposition of the external field and the field induced by magnetic moments of HTS grains. Meanwhile, analysis of the field width of the R(H) magnetoresistance hysteresis ΔH = Hdec − Hinc at Hdec = const, where Hinc and Hdec are increasing and decreasing branches of the R(H) hysteretic dependence, shows that the effective field in the intergrain medium exceeds by far both the external field and the field induced by magnetic moments of HTS grains. This situation suggests the magnetic flux compression in the intergrain medium because of the small length of grain boundaries, which amounts to ∼1 nm, i.e., is comparable with the coherence length and corresponds to Josephson tunneling in HTS materials. In this work, using the previously developed approach, we examine experimental data on the magnetoresistance and magnetization hysteresis in the granular YBa2Cu3O7 HTS compound in the range from 77 K to the critical temperature. According to the results obtained, the degree of magnetic flux compression determined by the parameter α in the expression for the effective field Beff(H) = H − 4π M(H) α in the intergrain medium remains constant over the investigated temperature range. All the features of the observed evolution of the R(H) hysteretic dependences are explained well within the proposed approach when the expression for Beff(H) contains the experimental M(H) magnetization data and the parameter α of about 20–25. The latter is indicative of the dominant effect of magnetic flux compression in the intergrain medium on the transport properties of granular HTS materials.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Korshunov M. M.
Заглавие : Itinerant spin fluctuations in iron-based superconductors
Место публикации : Perturbation theory: advances in research and applications. - New York: Nova Science Publishers, 2018. - Chap. 2. - P.61-137. - ISBN 9781536129908. - ISBN 9781536129892
Ключевые слова (''Своб.индексиров.''): fe-based superconductors--spin fluctuations--spin resonance peak--unconventional superconductivity
Аннотация: In multiband systems, it is possible to explore a variety of competing ground states. Bright examples are the Fe-based pnictides and chalcogenides, which demonstrate metallic, superconducting, and various magnetic phases. Here I discuss only one of the many interesting topics, namely, spin fluctuations in metallic multiband systems. I show how to calculate the effect of itinerant spin excitations on the electronic properties and formulate a theory of spin fluctuation-induced superconductivity. The superconducting state is unconventional and thus the system demonstrates unusual spin response with the spin resonance feature. I discuss its origin, consequences, and relation to experimental observations. Role of the spin-orbit coupling is specifically emphasized.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Aksenov S. V.
Заглавие : Spin-polarized-current switching mediated by Majorana bound states
Место публикации : J. Magn. Magn. Mater. - 2018. - Vol. 465. - P.88-92. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2018.04.043
Примечания : Cited References: 31. - We acknowledge fruitful discussions with A.D. Fedoseev and M.S. Shustin. The work was supported by the Comprehensive Programme SB RAS No. 0356-2015-0403 , Russian Foundation for Basic Research , Government of Krasnoyarsk Territory , Krasnoyarsk Region Science and Technology Support Fund to the research projects Nos. 16-02-00073 , 17-42-240441 . The work of S.V.A. was supported by grant of the President of the Russian Federation (MK-1398.2017.2).
Ключевые слова (''Своб.индексиров.''): majorana bound states--topological superconductivity--current-switch effect
Аннотация: We present the study of transport properties of a superconducting wire with strong Rashba spin-orbit coupling for different orientations of an external magnetic field. Using the nonequilibrium Green's functions in the tight-binding approach the crucial impact of the relative alignment of lead magnetization and the Majorana bound state (MBS) spin polarization on the low-bias conductance and shot noise is presented. Depending on this factor the transport regime can effectively vary from symmetric to extremely asymmetric. In the last situation the suppression of MBS-assisted conductance results in current-switch effect allowing the electrical detection of the Majorana fermions.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M., Korovushkin M. M., Barabanov A. F.
Заглавие : Stability of the superconducting d-wave pairing toward the intersite Coulomb repulsion in CuO2 plane
Место публикации : J. Low Temp. Phys. - 2018. - Vol. 191, Is. 5-6. - P.408-425. - ISSN 00222291 (ISSN), DOI 10.1007/s10909-018-1882-7
Примечания : Cited References: 70. - Acknowledgements The work was supported by the program of the Presidium of the Russian Academy of Sciences No. 12 “Fundamental problems of high-temperature superconductivity”, the Russian Foundation for Basic Research (RFBR) and partly by the Government of Krasnoyarsk Region and the Krasnoyarsk Region Science and Technology Support Fund (Projects Nos. 16-42-243057 and 16-42-240435). The work of A. F. B. was funded by RFBR (Project No. 16-02-00304). The work of M. M. K. was supported by a grant of the President of the Russian Federation (Project MK-1398.2017.2).
Ключевые слова (''Своб.индексиров.''): cuprate superconductors--unconventional superconductivity--spin-charge coupling--spin polarons--intersite coulomb interaction
Аннотация: Taking into account the real crystalline structure of the CuO2 plane and the strong spin-fermion coupling, we study the influence of the intersite Coulomb repulsion between holes on the Cooper instability of the spin-polaron quasiparticles in cuprate superconductors. The analysis shows that only the superconducting d-wave pairing is implemented in the whole region of doping, whereas the solutions of the self-consistent equations for the s-wave pairing are absent. It is shown that intersite Coulomb interaction V1 between the holes located at the nearest oxygen ions does not affect the d-wave pairing, because its Fourier transform Vq vanishes in the kernel of the corresponding integral equation. The intersite Coulomb interaction V2 of quasiparticles located at the next-nearest oxygen ions does not vanish in the integral equations, however, but it is also shown that the d-wave pairing is robust toward this interaction for physically reasonable values of V2.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Stolyar S. V., Balaev D. A., Ladygina V. P., Dubrovskiy A. A., Krasikov A. A., Popkov S. I., Bayukov O. A., Knyazev Yu. V., Yaroslavtsev R. N., Volochaev M. N., Iskhakov R. S., Dobretsov K. G., Morozov E. V., Falaleev O. V., Inzhevatkin E. V., Kolenchukova O. A., Chizhova I. A.
Заглавие : Bacterial ferrihydrite nanoparticles: preparation, magnetic properties, and application in medicine
Место публикации : J. Supercond. Novel Magn. - 2018. - Vol. 31, Is. 8. - P.2297-2304. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-018-4700-1
Примечания : Cited References: 37. - The electron microscopy examination was carried out at the Center for Collective Use of the Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences (Krasnoyarsk, Russia).
Ключевые слова (''Своб.индексиров.''): nanoparticles--ferrihydrite--magnetic properties--drug delivery
Аннотация: Nanoparticles of antiferromagnetically ordered materials acquire the uncompensated magnetic moment caused by defects and surface effects. A bright example of such a nano-antiferromagnet is nanoferrihydrite consisting of particles 2–5 nm in size, the magnetic moment of which amounts to hundreds of Bohr magnetons per particle. We present a brief review of the studies on magnetic properties of ferrihydrite produced by bacteria. Special attention is focused on the aspects of possible biomedical applications of this material, i.e., the particle elimination, toxicity, and possible use for targeted drug delivery.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Krasikov A. A., Dubrovskiy A. A., Balaev A. D., Popkov S. I., Kirillov V. L., Martyanov O. N.
Заглавие : Dynamic magnetization switching in NiO nanoparticles: Pulsed field magnetometry study
Место публикации : J. Supercond. Novel Magn. - 2019. - Vol. 32, Is. 2. - P.405–411. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-018-4726-4
Примечания : Cited References: 32. - We are grateful to Yu.V. Knyazev, S.V. Semenov, and M.I. Kolkov for their help and to M.N. Volochaev for the TEM measurements. TEM studies were performed on the facility of Resource Sharing Center of Krasnoyarsk Scientific Center of Siberian Branch of Russian Academy of Sciences.The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund to the research project no. 17-42-240138.
Ключевые слова (''Своб.индексиров.''): nio nanoparticles--pulsed field magnetization--coercivity
Аннотация: The dynamic magnetization switching of antiferromagnetic nickel oxide nanoparticles with a characteristic size of 8 nm has been experimentally investigated by pulsed field magnetometry. It is shown that, due to the presence of defects in NiO nanoparticles, as in other antiferromagnetic particles, the uncompensated magnetic moment is induced by the incomplete compensation of spins at the antiferromagnetic ordering. The dynamic magnetic hysteresis loops have been studied in pulsed fields with the maximum field (Hmax) of up to 130 kOe and pulse lengths (τP) of 4, 8, and 16 ms. According to the results obtained, the coercivity (HC) depends on both the τP and Hmax values. The observed increase in the HC value with decreasing pulse length (i.e., with increasing switching field frequency) is unambiguously related with the relaxation processes typical of single-domain ferromagnetic nanoparticles. However, the observed effect of the maximum applied field (Hmax) on the HC value is assumed to be a feature of antiferromagnetic nanoparticles.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shestakov V. A., Korshunov M. M., Togushova Yu.N., Efremov D. V., Dolgov O. V.
Заглавие : Details of the disorder-induced transition between s± and s++ states in the two-band model for Fe-based superconductors
Коллективы : Russian Foundation for Basic Research [16-02-00098]; Government Support of the Leading Scientific Schools of the Russian Federation [NSh-7559.2016.2]; 'BASIS' Foundation for Development of Theoretical Physics and Mathematics
Место публикации : Supercond. Sci. Technol. - 2018. - Vol. 31, Is. 3. - Ст.034001. - ISSN 0953-2048, DOI 10.1088/1361-6668/aaa501. - ISSN 1361-6668(eISSN)
Примечания : Cited References:62. - We are grateful to P D Grigor'ev and M V Sadovskii for useful discussions. This work was supported in part by the Russian Foundation for Basic Research (grant 16-02-00098) and Government Support of the Leading Scientific Schools of the Russian Federation (NSh-7559.2016.2). MMK and VAS acknowledge the support of the 'BASIS' Foundation for Development of Theoretical Physics and Mathematics.
Предметные рубрики: IRON-BASED SUPERCONDUCTORS
HIGH-TEMPERATURE SUPERCONDUCTIVITY
PAIRING
Ключевые слова (''Своб.индексиров.''): unconventional superconductors--iron pnictides--iron chalcogenides--impurity scattering
Аннотация: IIrradiation of superconductors with different particles is one of many ways to investigate the effects of disorder. Here we study the disorder-induced transition between s ± and s ++ states in the two-band model for Fe-based superconductors with nonmagnetic impurities. Specifically, we investigate the important question of whether the superconducting gaps during the transition change smoothly or abruptly. We show that the behavior can be of either type and is controlled by the ratio of intraband to interband impurity scattering potentials, and by a parameter σ, that represents scattering strength and ranges from zero (Born approximation) to one (unitary limit). For the pure interband scattering potential and the scattering strength σ ≲ 0.11, the s ± → s ++ transition is accompanied by steep changes in the gaps, while for larger values of σ, the gaps change smoothly. The behavior of the gaps is characterized by steep changes at low temperatures, T˂ 0.1Tc0 with Tc0 being the critical temperature in the clean limit, otherwise it changes gradually. The critical temperature Tc is always a smooth function of the scattering rate in spite of the steep changes in the behavior of the gaps.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Zlotnikov A. O.
Заглавие : Effect of the intersite Coulomb interaction on chiral superconductivity at the noncollinear spin ordering
Коллективы : Russian Foundation for Basic Research; Government of the Krasnoyarsk Territory; Krasnoyarsk Territorial Foundation for Support of Scientific and RD Activities [16-02-00073-a, 16-42-243057-r-mol-a]; Complex Program of the Siberian Branch of the Russian Academy of Sciences II.2P [0358-2015-002]; Grant of the President of the Russian Federation [SP-1370.2015.5]
Место публикации : Phys. Solid State. - 2017. - Vol. 59, Is. 11. - P.2120-2126. - ISSN 1063-7834, DOI 10.1134/S1063783417110300. - ISSN 1090-6460(eISSN)
Примечания : Cited References:18. - This study was supported by the Russian Foundation for Basic Research, Government of the Krasnoyarsk Territory, and Krasnoyarsk Territorial Foundation for Support of Scientific and R&D Activities, projects no. 16-02-00073-a and 16-42-243057-r-mol-a and the Complex Program of the Siberian Branch of the Russian Academy of Sciences II.2P, project no. 0358-2015-002. A.O. Zlotnikov is grateful for support of the Grant of the President of the Russian Federation SP-1370.2015.5.
Предметные рубрики: TRIANGULAR LATTICE
MAGNETIC ORDER
COEXISTENCE
PHASE
Аннотация: We investigate the effect of the intersite Coulomb interaction in a planar system with the triangular lattice on the structure of chiral order parameter Δ(p) in the phase of coexisting superconductivity and noncollinear 120° magnetic ordering. It has been established that the Coulomb correlations in this phase initiate the state where the quasi-momentum dependence Δ(p) can be presented as a superposition of the chiral invariants corresponding to the dx2−y2+idxy and px + ipy symmetry types. It is demonstrated that the inclusion of the Coulomb interaction shifts the Δ(p) nodal point positions and, thereby, changes the conditions for a quantum topological transition.
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12.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G.
Заглавие : Effect of electron-phonon interaction on the doping and temperature depended spectral function in cuprates
Коллективы : International Conference on Quantum in Complex Matter: Superconductivity, Magnetism and Ferroelectricity, Superstripes 2017. Quantum in Complex Matter: Superconductivity, Magnetism and Ferroelectricity
Место публикации : Superstripes 2017: [absrtacts]/ ed. A. Bianconi: Superstripes press, 2017. - Ст.37.1. - P.206. - (Science Series; Vol. 11). - ISBN 9788866830696
Аннотация: The generalized tight binding (GTB) method to calculate the electronic structure of strongly correlated electrons in cuprates is modified to incorporate also strong electronphonon interaction. By exact diagonalization of the p-d- Holstain model Hamiltonian for a separate CuO6 unit cell we find the multelectron and multiphonon local eigenstates that are used to construct a set of local Hubbard operators. Then we treat the intercell electron hopping t by the perturbation approach over small ratio t/U, where U is the charge transfer excitation energy. Without electron-phonon interaction we obtain the band of spin polaron and a set of local multiphonon Franck-Condon excitations. The electron-phonon interaction results in the hybridization of spin polaron and Franck Condon excitations that forms the polaronic band structure with strong temperature dependence. The temperature dependence of the polaronic band structure and Fermi surface is discussed. The peak of a spectral function at the top of the valence band has large width typical to the ARPES data and determined by a large number of the multiphonon excitations.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Zlotnikov A. O., Shustin M. S.
Заглавие : The nontrivial ground state topology in the coexistence phase of chiral d-wave superconductivity and 120 degrees magnetic order on a triangular lattice [Electronic resource]
Место публикации : ArXiv. - 2017. - Ст.1707.04422
Вид и объем ресурса: Electronic text data
Примечания : Cited References: 19. - This study was funded by the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, and Kranoyarsk Region Science and Techonology Support Fund according to the research projects Nos. 16-02-00073-a (calculation of the topological invariant of a 2D lattice) and 16-42-243069-mol-a (calculation of the Z2 invariant). A.O.Z. is grateful for support of the Grant of the President of the Russian Feeration SP-1370.2015.5. The work of M.S.S. was supported by the Grant of the President of the Russian Federation MK-1398.2017.2.
Ключевые слова (''Своб.индексиров.''): majorana zero modes--topological invariant--chiral superconductivity--noncollinear magnetic order--triangular lattice
Аннотация: The Z2 topological invariant is defined in the chiral d-wave superconductor having a triangular lattice in the presence of the 120 degrees magnetic ordering. By analyzing the Z2 invariant, we determine the conditions of implementing nontrivial phases in the model with regard to superconducting pairings between nearest and next nearest neighbors. It is often supposed in such system that the pairing parameter between nearest neighbors should be equal to zero due to influence of the intersite Coulomb interaction. We show that taking into account even weak pairings in the first coordination sphere leads to the disappearance of the gapless excitations of the bulk spectrum in the wide region of the parameter space. Thus topological invariants can be defined in such region. Solving the problem of open edges it is shown that the zero energy modes are realized basically in the topologically nontrivial phases. Such zero modes are topologically protected Majorana modes. A connection between the Z2 invariant calculated at the symmetric points of the Brillouin zone with respect to the electron-hole symmetry and the integer topological invariant of the ground state of the 2D lattice expressed in terms of the Green functions is established in the presence of noncollinear magnetic ordering.
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14.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Korshunov M. M.
Заглавие : Role of disorder in superconductivity of Fe-based systems
Коллективы : "Perspectives on High-Temperature Superconductivity", International Symposium, Skolkovo Institute of Science and Technology
Место публикации : Book of abstracts Int. symp. "Perspectives on high-temperature superconductivity". - 2017. - P.17
Примечания : Supported by RFBR (16-02-00098), government support of the leading scientific schools of the Russian Federation (NSh-7559.2016.2), and “BASIS” foundation for theoretical physics development
Аннотация: Disorder can result in interesting and sometimes unexpected effects in multiband superconductors. Especially if the superconductivity is unconventional like in ironbased pnictides and chalcogenides. I’m going to discuss how the impurity scattering affects superconducting states with s+- and s++ gaps, and show that disorder causes the transitions between s+- and s++ states and examine observable effects these transitions can produce.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Yakushkin S. S., Balaev D. A., Dubrovskiy A. A., Semenov S. V., Shaikhutdinov K. A., Kazakova M. A., Bukhtiyarova G. A., Martyanov O. N., Bayukov O. A.
Заглавие : Evolution of the Fe3+ ion local environment during the phase transition ε-Fe2O3 → α-Fe2O3
Место публикации : J. Supercond. Nov. Magn. - 2018. - Vol. 31, Is. 4. - P.1209–1217. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-017-4307-y
Примечания : Cited References: 37. - The work was supported by the Russian Science Foundation (Grant No. 17-12-01111).
Ключевые слова (''Своб.индексиров.''): ε−fe2o3 iron oxide nanoparticles--phase transition--structure size effect--magnetic properties--mossbauer spectroscopy
Аннотация: Evolution of the local environment of Fe3+ ions in deposited Fe2O3/SiO2 nanoparticles formed in samples with different iron contents was investigated in order to establish the conditions for obtaining the stable ε-Fe2O3/SiO2 samples without impurities of other iron oxide polymorphs. Microstructure of the samples with an iron content of up to 16% is studied by high-resolution transmission electron microscopy, X-ray diffraction analysis, and Mössbauer spectroscopy, and their magnetic properties are examined. At iron concentrations below 6%, calcinations of iron-containing precursor nanoparticles in a silica gel matrix lead to the formation of the ε-Fe2O3 iron oxide polymorphic modification without foreign phase impurities, while at the iron concentration in the range of 6–12%, the hematite phase forms in the sample in the fraction of no more than 5%. It is concluded on the basis of the data obtained that the spatial stabilization of iron-containing particles is one of the main factors facilitating the formation of the ε-Fe2O3 phase in a silica gel matrix without other iron oxide polymorphs. It is demonstrated that the increase in the iron content leads to the formation of larger particles in the sample and gradual changes of the Fe3+ ion local environment during the phase transition ε-Fe2O3 → α-Fe2O3.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gokhfeld D. M.
Заглавие : Use of a sigmoid function to describe second peak in magnetization loops
Место публикации : J. Supercond. Nov. Magn. - 2018. - Vol. 31, Is. 6. - P.1785–1789. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-017-4400-2
Примечания : Cited References: 35
Ключевые слова (''Своб.индексиров.''): peak effect--fishtail--magnetization--critical current--order-disorder transition--boltzmann function--extended critical state model--phase separation--type ii superconductor
Аннотация: Order-disorder transitions of a vortex lattice transfer type-II superconductors from a low critical current state to a high one. The similar transition between different current states can be caused by electromagnetic granularity. A sigmoid curve is proposed to describe the corresponding peak in a field dependence of the macroscopic critical density. Using the extended critical state model, analytic expressions are obtained for the field dependencies of the local critical current density, the depth of equilibrium surface region, and the macroscopic critical current density. The expressions are well fit to published data.Фазовые переходы вихревой решетки из упорядоченного в разупорядоченное состояние переводят сверхпроводник второго рода из состояния с низким критическим током в состояние с большим критическим током. Похожий переход между различными токовыми состояниями может быть вызван электромагнитной гранулярностью. Для описания возникающего пика на полевой зависимости плотности критического тока предложена сигмоидальная кривая. В рамках расширенной модели критического состояния получены аналитические выражения для полевых зависимостей локальной плотности критического тока, глубины равновесного поверхностного слоя и макроскопической плотности критического тока. Выражения хорошо описывают известные экспериментальные данные.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Zlotnikov A. O., Shustin M. S.
Заглавие : The nontrivial ground state topology in the coexistence phase of chiral d-wave superconductivity and 120-degree magnetic order on a triangular lattice
Коллективы : Moscow International Symposium on Magnetism
Место публикации : J. Magn. Magn. Mater. - 2018. - Vol. 459. - P.112-117. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2017.11.115
Примечания : Cited References: 19. - This study was funded by the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, and Krasnoyarsk Region Science and Technology Support Fund according to the research projects No. 16-02-00073-a and 16-42-243069-mol-a. A.O.Z. is grateful for the support of the Grant of the President of the Russian Federation SP-1370.2015.5. The work of M.S.S. was supported by the Grant of the President of the Russian Federation MK-1398.2017.2.
Ключевые слова (''Своб.индексиров.''): majorana zero modes--topological invariant--chiral superconductivity--noncollinear magnetic order--triangular lattice
Аннотация: The Z2 topological invariant is defined in the chiral d-wave superconductor having a triangular lattice in the presence of the 120-degree magnetic ordering. Analyzing the Z2 invariant, we determine the conditions of implementing topological phases in the model with regard to superconducting pairings between the nearest and next nearest neighbors. It is often supposed in such a system that the pairing parameter between the nearest neighbors should be equal to zero due to the intersite Coulomb interaction. We show that taking into account even weak pairings in the first coordination sphere leads to the disappearance of the gapless excitations of the bulk spectrum in the wide region of the parameter space. Thus, topological invariants can be defined in this region. In solving the problem of open edges it is shown that the zero energy modes are realized basically in the topologically nontrivial phases. Such zero modes are topologically protected Majorana modes. A connection between the Z2 invariant and the integer topological invariant of the ground state of the 2D lattice is established in the presence of the electron-hole symmetry and noncollinear magnetic ordering.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Stolyar S. V., Balaev D. A., Krasikov A. A., Dubrovskiy A. A., Yaroslavtsev R. N., Bayukov O. A., Volochaev M. N., Iskhakov R. S.
Заглавие : Modification of the structure and magnetic properties of cobalt-doped ferrihydrite nanoparticles under heat treatment
Место публикации : J. Supercond. Nov. Magn. - 2018. - Vol. 31, Is. 4. - P.1133-1138. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-017-4263-6
Примечания : Cited References: 29. - The reported study was funded by Russian Foundation for Basic Research and Krasnoyarsk region according to the research project №17-43-240527 and Russian Foundation for Basic Research project №16-03-00969. Support by the Special Program for Siberian Federal University of the Ministry of Education and Science of the Russian Federation is acknowledged.
Ключевые слова (''Своб.индексиров.''): nanoparticles--ferrihydrite--magnetic properties--structure
Аннотация: Nanoparticles of antiferromagnetic materials acquire the magnetic moment due to the surface effects and structural defects. According to the Neel hypothesis, magnetic moment μP of a particle containing N magnetically active atoms with magnetic moment J can be estimated as μP ∼ J · Nn or μP ∼ Vn, where V is the particle volume. Numerous studies of the magnetic properties of ferrihydrite 5Fe2O3⋅9H2O and ferritin revealed a value of n ≈ 1/2 for this material, in which Fe atoms have the octahedral surrounding of anions. We investigate the effect of low-temperature annealing of cobalt-doped ferrihydrite nanoparticles on their average size and magnetic properties. Using the Mössbauer spectroscopy study, we demonstrate that doping with Co makes Fe atoms enter the anion tetrahedra which leads to an increase in the exponent n〉1/2 in the expression μP ∼ J · Nn.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Zlotnikov A. O.
Заглавие : Topological phase of coexisting superconductivity and 120-degree magnetic order on a triangular lattice
Место публикации : Bull. Russ. Acad. Sci. Phys. - 2018. - Vol. 82, Is. 5. - P.588-590. - ISSN 10628738 (ISSN), DOI 10.3103/S1062873818050325
Примечания : Cited References: 12. - This study was supported by the Russian Foundation for Basic Research, the Government of Krasnoyarsk krai, and the Krasnoyarsk Territorial Foundation for Science and Technology, project nos. 16-02-00073, 17-42-240441, and 16-42-243069. A.O. Zlotnikov acknowledges the support of the RF Presidential Grant Council, project nos. SP-1370.2015.5 and MK-1398.2017.2.
Ключевые слова (''Своб.индексиров.''): linear combinations--nontrivial topology--self-consistent calculation--spin wave approximation--sublattice magnetization--superconducting order parameters--topological phase--triangular lattice
Аннотация: Using the t–J–V model, self-consistent calculations of the superconducting order parameter described by a linear combination of dx2−y2+idxy and p x + ip y chiral invariants are performed in the phase of coexistence with 120-degree magnetic ordering. Sublattice magnetization is determined in the spin-wave approximation for the case of half-filling. A nontrivial topology of the coexistence phase is demonstrated, testifying to the possibility of obtaining edge states and Majorana modes.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Semenov S. V., Balaev A. D., Balaev D. A.
Заглавие : Dissipation in granular high-temperature superconductors: New approach to describing the magnetoresistance hysteresis and the resistive transition in external magnetic fields
Коллективы : Russian Science Foundation [17-72-10050]
Место публикации : J. Appl. Phys. - 2019. - Vol. 125, Is. 3. - Ст.033903. - ISSN 0021-8979, DOI 10.1063/1.5066602. - ISSN 1089-7550(eISSN)
Примечания : Cited References: 79. - The work was supported by the Russian Science Foundation (Grant No. 17-72-10050). We are grateful to K. Terent'ev for the preparation of the sample and D. Gokhfeld for useful discussions.
Предметные рубрики: CRITICAL-CURRENT-DENSITY
VORTEX-GLASS SUPERCONDUCTIVITY
ANISOTROPIC ENERGY-DISSIPATION
Аннотация: An approach to describing the R(H) magnetoresistance hysteresis in granular high-temperature superconductors and behavior of the R(T) resistive transition in these objects in an external magnetic field is proposed. The dissipation is attributed to the subsystem of intergrain boundaries, which form a Josephson junction network. The approach is based on accounting for the effect of magnetic moments of superconducting grains on the resulting (effective) field in the intergrain medium. The described procedure includes (i) establishing of the degree of magnetic flux crowding in the intergrain medium by comparing the experimental data on the R(H) magnetoresistance hysteresis and magnetization M(H), (ii) determining the effective field Beff in the intergrain medium as a function of external field H and temperature T with regard to the thermomagnetic prehistory, and (iii) fitting the experimental R(H) and R(T) dependences using the Arrhenius expression R ∼ exp(–EJ/ kB T), where EJ is the parameter corresponding to the Josephson coupling energy. The fundamental novelty of the proposed approach is the extraction of the functional dependences of EJ on the effective field Beff in the intergrain medium rather than on the external field H, as was made in many previous works. It is shown that the proposed approach makes it possible to adequately describe both the R(H) hysteretic dependences and R(T) dependences of the Y-Ba-Cu-O high-temperature superconductor samples with different morphologies and critical current densities.
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