Gap anisotropy and van Hove singularities in high-Tc superconductors

Bouvier, J.; Bok, J.

doi:10.1016/0921-4534(95)00294-4

Cited by 41 publications

(35 citation statements)

References 22 publications

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“…As is known, the anisotropy of a superconducting order parameter Δ can be caused by the following factors: basic deviation of the symmetry type from the s-wave, i.e., by the presence of an angular gap amplitude distribution Δ(θ) in the k-space [101,102]; the splitting of the gap amplitude, due to degeneracy removing for condensate, realized on the Fermi surfaces with similar geometry and slightly different momentum modules (e.g., nested); by the variation of the gap in the real space, for example due to an inhomogeneous distribution of impurities or dopant.…”

Section: The Effect Of Multiple Andreev Reflectionsmentioning

confidence: 99%

“Break-junction” technique in application to layered superconductors (Review Article)

Kuzmichev

Kuzmicheva

2016

Low Temperature Physics

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Here presented a systematic study of superconductor-constriction-superconductor contacts realized by a break-junction technique in layered superconductors. Depending on the constriction transparency the tunneling and SnS-Andreev spectroscopies could be used, for the direct determination of values of superconducting gaps, characteristic BCS-ratios and gap temperature dependences in cuprate superconductors, magnesium diboride, novel pnictides and chalcogenides. Basing on these data, one can estimate the gap anisotropy magnitude as well as values of electron-boson coupling constants. We discuss the advantages and difficulties of the break-junction technique and demonstrate this method is powerful enough for high-resolution investigation of optical phonon modes in high-temperature superconducting cuprates and for creating of the contacts with the selective transparence in Mg 1-x Al x B 2 compounds.In memory of Ya. G. Ponomarev, professor, our teacher, warrior, and outstanding experimenter. In memory of S. N. Tchesnokov, mentor, friend, and extraordinary inventor

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Section: The Effect Of Multiple Andreev Reflectionsmentioning

confidence: 99%

“Break-junction” technique in application to layered superconductors (Review Article)

Kuzmichev

Kuzmicheva

2016

Low Temperature Physics

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“…In the presence of on-site Coulomb repulsion, extremely anisotropic s-wave order parameter with nodes was obtained [18]. Bouvier and Bok also calculated an order parameter explicitly, and obtained anisotropic s-wave in the same model [19]. Recently, it has been shown that d-wave superconductivity is reproduced in a similar model with antiferromagnetic fluctuations [20,21].…”

Section: Introductionmentioning

confidence: 85%

“…For the rapid increase of λ 1 , the condition λ 0 −ũ < λ 1 is realized more easily in layer systems than in usual three dimensional systems, where λ 0 denotes the s-wave coupling constant and −ũ is a negative contribution to swave pairing due to the short-range Coulomb repulsion discussed near eq. (19). Hence triplet pairing superconductivity is favored in layered compounds.…”

Section: Discussion and Summarymentioning

confidence: 99%

Anisotropic superconductivity mediated by phonons in layered compounds with weak screening effects

Seki

Kohmoto

2002

Phys. Rev. B

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Anisotropic pairing interactions mediated by phonons are examined in layer systems. It is shown that the screening effects become weaker when the layer spacing increases. Then the anisotropic components of the pairing interactions increase with the screening length since the momentum dependence changes. As a result, various types of anisotropic superconductivity occur depending on the parameter region. For example, p-wave superconductivity occurs when the short-range part of Coulomb repulsion is strong and the layer spacing is large. Two kinds of inter-layer pairing may occur when the layer spacing is not too large. Although the phonon contribution to the d-wave pairing interaction is weaker than the p-wave interaction, it increases with the layer spacing. Relevance of the present results to organic superconductors, high-Tc cuprates, and Sr2RuO4 is discussed.

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“…This interaction has been examined by many authors [6][7][8][9] for the high-T c superconductivity. As explained in the text books, near the Fermi surface where |ξ| < ∼ ω(q), the interaction is attractive due to overscreening.…”

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confidence: 99%

“…The momentum dependence of the pairing interactions was examined, where screening effect was taken into account. Bouvier and Bok calculated the superconducting gap and obtained anisotropic momentum dependence of the gap function [7] in the same model. Recently, Friedel and Kohmoto [8], and Chang, Friedel, and Kohmoto [9] have shown that d-wave superconductivity is induced by screened phonon interactions with an assist of a contribution from the antiferromagnetic fluctuations.…”

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confidence: 99%

Triplet superconductivity induced by screened phonon interactions in ferromagnetic compounds

Seki

Kohmoto

2002

Europhys. Lett.

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We propose that screened pairing interactions mediated by phonons could give rise to a spin triplet superconductivity in ferromagnetic compounds such as UGe2. It is pointed out that the pairing interactions include anisotropic components such as those of p, d, f -waves in addition to dominant s-wave component due to the momentum dependence. Since the ferromagnetic longrange order coexists, there is a large splitting of the Fermi surfaces of up and down spin electrons, which suppresses singlet pairing. Therefore, triplet pairing occurs at last due to the sub-dominant anisotropic interactions, even in the absence of magnetic contribution to the pairing interactions.Recently, a coexistence of superconductivity and ferromagnetic long-range order was observed in UGe 2 under pressure [1]. In the phase diagram on the pressure and temperature plane the superconductivity appears inside the area of the ferromagnetic phase. For this proximity of the superconductivity and the ferromagnetism, spin triplet superconductivity is a possible candidate in this compound.In addition, singlet pairing is considered to be unfavalable in this compound. The ferromagnetism and superconductivity occur in the same electron band [1,2] or at least in very close electron bands from the crystal structure. Thus, there is a large Fermi surface splitting, which suppresses antiparallel spin pairing, in the electron band responsible to the superconductivity.As a mechanism of triplet pairing, magnetically mediated superconductivity has been considered [1]. However, there are some behaviors which are not easily explained only by this mechanism. For example, the magnetic fluctuations and their contribution to the pairing interactions increase near the transition points. Such behavior is reproduced in the calculation of Fay and Appel [3]. In their calculation, it decreases in a narrow region of the width of 1% of the exchange interaction parameter near the second order transition point, but this decrease would not occur in UGe 2 , since the magnetic transition is of first order in UGe 2 . Therefore, the superconducting transition temperature seems to increase as the magnetic boundary is approached in this mechanism. However, in the observation, T c decreases near the phase boundary (∼ 1.6GPa) within the width of ∼ 0.3GPa of the pressure, which is not very narrow.Decreases of the superconducting transition temperatures as the magnetic phase approached were also observed in high-T c superconductors. However, in those compounds, the magnetic phase is antiferromagnetism. Thus, we have a physical explanation of the decrease of the superconducting transition temperature based on the reduction of the density of states near the Fermi surface (pseudogap) due to the antiferromagnetic fluctuations [4]. On the other hand, the ferromagnetic fluctuations do not induce any pseudogap near the Fermi surface, since it is split to two surfaces.On the other hand, if the decrease of the superconducting transition temperature near the magnetic phase boundary at the high pres...

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Gap anisotropy and van Hove singularities in high-Tc superconductors

Cited by 41 publications

References 22 publications

“Break-junction” technique in application to layered superconductors (Review Article)

“Break-junction” technique in application to layered superconductors (Review Article)

Anisotropic superconductivity mediated by phonons in layered compounds with weak screening effects

Triplet superconductivity induced by screened phonon interactions in ferromagnetic compounds

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