The high-T<sub>c</sub>superconductors: a conservative view

Friedel, J.

doi:10.1088/0953-8984/1/42/001

Cited by 193 publications

(203 citation statements)

References 227 publications

(46 reference statements)

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“…8 This reduction was attributed to a pseudo-gap, a notion first introduced by Friedel. 9 As we shall see, it occurs when the pseudo-gap becomes distinct from the coherence energy scale. 10 We show that by selecting a doping range where this difference is reduced, it is possible to greatly improve vortex pinning under strong applied fields, thus enhancing the prospects for high field-high current applications of HTS such as MMR magnets above 1 GHz and user magnets above 30T.…”

mentioning

confidence: 88%

“…11 The pseudo-gap was first introduced by Friedel to describe the changes in quasi-particle behavior brought on by the near formation of a spin density wave. 9 Tunneling measurements showed that the density of states peaks at an energy scale p , called the pseudo-gap because it is seen already above T c . It increases as doping is reduced, 11 consistent with the trend observed by Loram.…”

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confidence: 99%

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Impact of pseudo-gap states on the pinning energy and irreversibility field of high temperature superconductors

Deutscher

2014

Apl Materials

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The existence of pseudo-gap states at energies larger than the coherence energy scale is shown to be at the origin of the difficulties encountered in achieving strong vortex pinning in the high Tc cuprates. Reduction or elimination of the pseudo-gap states by overdoping is effective in increasing the condensation energy and the irreversibility field. In YBa2Cu3O7, a full BCS state, with a single energy scale, can be restored, leading to the highest known irreversibility field and pinning strength. In the bismuthates, the detrimental effect of the pseudo-gap states can only be mitigated to some extent by overdoping.

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confidence: 88%

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confidence: 99%

Impact of pseudo-gap states on the pinning energy and irreversibility field of high temperature superconductors

Deutscher

2014

Apl Materials

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“…The same applies to more exotic pairing schemes such as the odd-gap pairing 145 , where the usual scattering suppression of T c is also very strong. Among mechanisms discussed for high-T c superconductors we should also mention different types of so-called van-Hove scenarios [146][147][148][149] , which are based upon the idea of T cenhancement due to some kind of the density of states singularity close to the Fermi level. For all such mechanisms rather strong T c suppression may be due to the potential scattering smoothing out these singularities.…”

Section: B T C Degradationmentioning

confidence: 99%

Superconductivity and localization

1997

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We present a review of theoretical and experimental works on the problem of mutual interplay of Anderson localization and superconductivity in strongly disordered systems. Superconductivity exists close to the metalinsulator transition in some disordered systems such as amorphous metals, superconducting compounds disordered by fast neutron irradiation etc. Hightemperature superconductors are especially interesting from this point of view. Only bulk systems are considered in this review. The superconductor-insulator transition in purely two-dimensional disordered systems is not discussed.We start with brief discussion of modern aspects of localization theory including the basic concept of scaling, self-consistent theory and interaction effects. After that we analyze disorder effects on Cooper pairing and superconducting transition temperature as well as Ginzburg-Landau equations for superconductors which are close to the Anderson transition. A necessary generalization of usual theory of "dirty" superconductors is formulated which allows to analyze anomalies of the main superconducting properties close to disorder-induced metal-insulator transition. Under very rigid conditions superconductivity may persist even in the localized phase (Anderson insulator).Strong disordering leads to considerable reduction of superconducting transition temperature T c and to important anomalies in the behavior of the upper critical field H c2 . Fluctuation effects are also discussed. In the vicinity of Anderson transition inhomogeneous superconductivity appears due to statistical fluctuations of the local density of states.We briefly discuss a number of experiments demonstrating superconductivity close to the Anderson transition both in traditional and high-T c superconductors. In traditional systems superconductivity is in most cases destroyed before metal-insulator transition. In case of high-T c superconductors a number of anomalies show that superconductivity is apparently conserved in the localized phase before it is suppressed by strong enough disorder. The concept of electron localization 1 is basic for the understanding of electron properties of disordered systems 2,3 . In recent years a number of review papers had appeared, extensively discussing this problem [4][5][6][7] . According to this concept introduction of sufficiently strong disorder into a metallic system leads to spatial localization of electronic states near the Fermi level and thus to a transition to dielectric state (Anderson transition). After this transition dc conductivity (at zero temperature, T = 0) vanishes, despite the finite value of electronic density of states at the Fermi level (at least in one-electron approximation).At the same time it is well-known that even the smallest attraction of electrons close to the Fermi level leads to formation of Cooper pairs and the system becomes superconducting at sufficiently low temperatures 8,9 . It is known that the introduction of disorder which does not break the time-reversal invariance (normal, nonm...

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“…Moreover, the transition is complete only at a fixed hole density, x ∼ 0.125 [3]. These features can be understood [4] in terms of the LTT phase splitting the degeneracy of the two van Hove singularities (vHs's) [5][6][7], at the X-and Y -points of the (HTT) Brillouin zone.…”

Section: Introductionmentioning

confidence: 99%

Van Hove excitons and high-Tc superconductivity

Markiewicz

1993

Physica C: Superconductivity

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The possible role of the van Hove singularity (vHs) in stabilizing the low-temperature orthorhombic (LTO) phase transition in La 2−x Sr x CuO 4 (LSCO) is discussed. It is found that the vHs can drive a structural distortion in two different ways, either due to spin-orbit coupling or to dynamic Jahn-Teller (JT) effects. This paper discusses the latter effect in some detail. It is shown that a model Hamiltonian introduced earlier to describe the coupled electron -octahedral tilt motions ('cageons') has a series of phase transitions, from a high-temperature disordered JT phase (similar to the high-temperature tetragonal phase of LSCO) to an intermediate temperature dynamic JT phase, of average orthorhombic symmetry (the LTO phase) to a low temperature static JT phase (the low temperature tetragonal phase). For some parameter values, the static JT phase is absent.

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The high-T_csuperconductors: a conservative view

Cited by 193 publications

References 227 publications

Impact of pseudo-gap states on the pinning energy and irreversibility field of high temperature superconductors

Impact of pseudo-gap states on the pinning energy and irreversibility field of high temperature superconductors

Superconductivity and localization

Van Hove excitons and high-Tc superconductivity

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The high-Tcsuperconductors: a conservative view

Cited by 193 publications

References 227 publications

Impact of pseudo-gap states on the pinning energy and irreversibility field of high temperature superconductors

Impact of pseudo-gap states on the pinning energy and irreversibility field of high temperature superconductors

Superconductivity and localization

Van Hove excitons and high-Tc superconductivity

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The high-T_csuperconductors: a conservative view