Superconductivity of overdoped cuprates: the modern face of the ancestral two-electron exchange

Mishonov, Todor M.; Indekeu, Joseph; Penev, Evgeni S.

doi:10.1088/0953-8984/15/25/312

Cited by 11 publications

(14 citation statements)

References 198 publications

(210 reference statements)

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“…Such a situation occurred earlier in a band calculation for high-T c superconductors. 27,28 The second aspect mentioned in the preamble is that the BCS approximation itself has a low precision and should be substituted by the Eliashberg formalism. The numerical calculations by Golubov et al 3 indicate that the Eliashberg weight function is very small in a broad range of low energy and has rather sharp peaks in the range of 800-1000 K. This is an unusual situation.…”

Section: ͑11͒mentioning

confidence: 99%

Thermodynamics ofMgB2described by the weak-coupling two-band BCS model

2005

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Based on weak-coupling anisotropic BCS theory, the temperature dependence of energy gap and the specific heat are evaluated for the MgB 2 superconductor, and the results are compared with experimental data. We show that the weak-coupling anisotropic BCS theory describes thermodynamic experimental data with high precision, 3-6%. DOI: 10.1103/PhysRevB.71.012514 PACS number͑s͒: 74.70.Ad, 74.20.Fg, 74.25.Bt A keen interest excited by discovery and experimental investigation of a new high T c superconductor MgB 2 is to a large extent associated with its dissimilarity to cuprate superconductors. The superconductivity of MgB 2 is definitely a three-dimensional effect, whereas in cuprates it is presumably two-dimensional ͑2D͒. Nevertheless, the superconducting gap in MgB 2 displays strong anisotropy. The most precise tunneling measurements by Gonnelli et al. 1 give the value 2.6 for the ratio of the gaps at two conductivity bands. On the other hand, the measured gaps are the same for the tunneling in the ab-plane and in the c-direction, indicating that they do not depend on direction within each piece of the Fermi surface.An important problem is how strong is the interaction in MgB 2 . First-principles calculations 2-4 indicate that electronphonon interaction is not weak and that the Eliashberg description is appropriate. However, anisotropy and interaction were shown to influence thermodynamics oppositely. For example, the anisotropy decreases the relative discontinuity of the specific heat at the transition point, 5,6 whereas the first correction due to interaction increases it.7 Besides, MgB 2 is a very hard material with a high value of Debye frequency, which usually correlates with a weak coupling. Therefore it is not a priori clear what is more substantial in the case of MgB 2 .The purpose of our work is to demonstrate that the anisotropy effects are more substantial at least for thermodynamic measurements. We show that, as a matter of fact, the weak coupling anisotropic BCS theory describes all known thermodynamic experimental data including the temperature dependence of the energy gap and specific heat with a high precision, 3-6%.The main features of the anisotropic weak coupling BCS model were elucidated in the early 1960s, 5,6,[8][9][10] the ultimate result being the factorization of the gap 5 ⌬͑T,k͒ = Q͑T͒͑k͒, ͑1͒ which was experimentally verified by Zavaritskii. 11 The function of angle ͑k͒ is the eigenfunction of the interaction operator V͑k , kЈ͒ corresponding to the maximal eigenvalue + . It satisfies the linear homogeneous integral equation:

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Section: ͑11͒mentioning

confidence: 99%

Thermodynamics ofMgB2described by the weak-coupling two-band BCS model

2005

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“…Mishonov et al proposed an inter-atomic two-electron exchange [49]. In contrast with this previous proposals, these authors recently have advanced the intra-atomic exchange of two electrons between 4s and 3d x 2 −y 2 states as the origin of high T c superconduction in cuprates [50,51]. In our opinion, identification of exchange interactions as the very cause of superconductivity represents a major progress in this field of studies.…”

Section: Discussionmentioning

confidence: 97%

Theory of High Temperature Superconductivity

Fujita¹,

Godoy²

2001

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Abstract.We deal with a model for high-temperature superconductivity which maintains that in cuprates spin-singlet bonds are formed between electrons running in the neighbouring layers of copper oxide found in lattice of these materials. This model reutilizes the BCS scheme, but with the essential difference that the electron pairs are characterized by equal, rather than opposite, momenta as in Cooper pairs. In the present paper, we consider the electron pair formation and a peculiar canonical transformation analogous to the transformation once applied to the theory of pairing correlations in nuclear matter. It is shown that the quasi-particle energy spectrum remains that of the BCS theory, including the linear relationship between forbidden energy gap and critical temperature. The model is also applied to superconductivity of some copperless perovskites of mixed stoichiometry, whose features are of special worth in understanding the mechanism of the phenomenon. The possibility of enhancing critical temperature in cuprates by inserting monovalent ions into the lattice is considered.PACS: 74.20.-z; 74.72.JT.

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“…Отметим, что имеется значительное число статей и обзоров последних лет, посвященных теории ВТСП [1], в которых можно найти дальнейшие ссылки. Не вдаваясь в детали различных теоретических моделей, отметим, что все они указывают на существенную роль спиновых, зарядовых и парных флуктуаций в установлении явления сверхпроводимости и подчеркивают роль двухэлектронного обмена между различными орбиталями, принадлежащими разным атомам [2] или одному и тому же атому [3].…”

Section: Introductionunclassified

Особенности Парного Взаимодействия В Четырехзонной Модели Хаббарда

Дигор¹,

Entel²,

Moskalenko³

et al. 2006

ТМФ

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Рассмотрена четырехзонная модель высокотемпературных сверхпроводников, содержащая 3d x 2 −y 2-и 4s-электроны меди и 2px-и 2py-электроны кислорода. Предполагается сильное кулоновское отталкивание 3d-электронов меди. Выполнена диагонализация кислородной подсистемы и переход к представлению Ванье для кластера CuO2. Изучены свойства локальной ячеечной модели и определены такие ее низшие по энергии состояния, как одночастичный дублет и двухчастичные синглетные и триплетные состояния. Рассмотрены процессы делокализации фермионов ячейки, вызванные их туннелированием между узлами меди. Получена система уравнений типа Дайсона для перенормированных одночастичнных функций Грина и обсуждена возможность ее упрощения. Ключевые слова: сильно коррелированные электронные системы, высокотемпературные сверхпроводники.

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Superconductivity of overdoped cuprates: the modern face of the ancestral two-electron exchange

Cited by 11 publications

References 198 publications

Thermodynamics ofMgB2described by the weak-coupling two-band BCS model

Thermodynamics ofMgB2described by the weak-coupling two-band BCS model

Theory of High Temperature Superconductivity

Особенности Парного Взаимодействия В Четырехзонной Модели Хаббарда

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