Schrama<i>et al.</i>Reply:

Schrama, J. M.; Singleton, John

doi:10.1103/physrevlett.86.3453

Cited by 51 publications

(71 citation statements)

References 13 publications

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“…This dichotomy is also found in the many studies of temperature dependence of the London penetration depth, which is well known for providing both power-law (node) behavior (Kanoda et al 1990, Le et al 1992, Achkir et al 1993, Tsubokura et al 1995, Carrington et al 1999, Pinteric et al 2000, Pratt et al 2001) and activated (nodeless) behavior (Harshman et al 1990, 1994, Klein et al 1991, Lang et al 1992a,b, 1994, Dressel et al 1993, 1994. Several other types of experiments have indicated gap nodes: thermal conductivity (Belin et al 1998, Izawa et al 2002b), millimeter-wave cavity absorption (Schrama et al 1999, Schrama andSingleton 2001), and tunnelling (Arai et al 2001). Earlier tunnelling work by the same team (of Arai et al 2001) had, however, found gap anisotropy without nodes (Nomura et al 1995, Ichimura et al 1997.…”

Section: Planar Organicsmentioning

confidence: 86%

Strongly anisotropic s-wave gaps in exotic superconductors

Brandow

2003

Philosophical Magazine

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The exotic superconductors, defined as those which follow the phenomenological trend of Uemura (T c approximately µ l L -2 ), presently constitute the most broad and general class of superconductors which can reasonably be considered "similar to the high-T c cuprates". It is therefore of much interest to determine the forms of their pairing gap functions. We examine evidence for the gap forms in non-cuprate exotics, and demonstrate some general features. The cubic materials often have highly anisotropic gaps. The planar materials tend to have even stronger gap anisotropy, to the extent that they often have gap nodes, but nevertheless they usually have an s-wave-like gap symmetry. There is good evidence for the latter even in the controversial cases of planar organics and nickel borocarbides. Exceptions to these generalizations are also pointed out and discussed. §1. INTRODUCTIONThere are now many unusual superconductors which are recognized to share some of the novel features of the high-T c cuprate superconductors. The possibility of further similarity to the cuprates, in particular the possibility of pairing by exchange of a virtual spin fluctuation or paramagnon, has motivated suggestions of d-wave gap forms in some of these other superconductors, in cases where there is evidence for gap nodes. This argument has been applied especially to the planar organics and sometimes also to the 2 nickel borocarbides, in addition to the well known cases of heavy-fermion materials. This line of reasoning calls for a careful examination of the evidence for the gap forms in these and other unusual superconductors.In this paper we focus on the exotic superconductors of Uemura and co-workers. 1 These exotics include a number of the unusual superconductors of earlier (pre-cuprate) interest, as well as the cuprates themselves and others discovered after the cuprates, and they include most of the materials previously suggested as being similar to the cuprates. 2 As discussed below, they now constitute the most broad and general class of superconductors that can reasonably be considered similar to the cuprates. (The variety of crystal structures and material chemistries in this class of materials is remarkably extensive.2 ) It is therefore very reasonable to focus on these materials. We now examine many of the non-cuprate exotic materials and material families, those for which there is reasonable gap-form evidence, in order to establish two general conclusions about their superconducting phenomenology: (1) In the cubic and nearly-cubic materials, which are conventionally expected to have nearly isotropic gaps, there is often evidence of very strong gap anisotropy. Sometimes there even appear to be gap nodes, although the gap symmetry remains s-wave-like. (2) In the planar (quasi-two-dimensional) materials there are often gap nodes, but nevertheless they typically still have an s-wave-like gap symmetry.[Here s-wave-like means having the full point-group symmetry of the crystal structure, a condition which does allow the p...

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Section: Planar Organicsmentioning

confidence: 86%

Strongly anisotropic s-wave gaps in exotic superconductors

Brandow

2003

Philosophical Magazine

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“…For the present organic superconductors, these techniques include mm-wave transmission [334], STM spectroscopy [335] and thermal conductivity [62] studies. A mm-wave magneto-optical technique was used to determine the angle dependence of the high-frequency conductivity of κ-(ET) 2 Cu(NCS) 2 [334,336]. The results have been interpreted to support an anisotropic gap with "X shape", i.e.…”

Section: Superconductivity-induced Phonon Renormalizationmentioning

confidence: 99%

Organic Superconductors

Lang

Müller

2004

The Physics of Superconductors

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“…It is interesting to speculate as to why the heat capacity data should imply such a different superconducting groundstate from the other experimental probes. Discussion on this matter has encompassed experimental difficulties, including the possible field dependence of the thermometry used [114], the extreme difficulty in subtracting the other contributions to the heat capacity, the presence of other fielddependent contributions to the heat capacity [114,115] and the evolution of the form of the superconducting order parameter with magnetic field [116]. At present, the matter is unresolved.…”

Section: Penetration-depth Muon Spin Rotation and Thermal Conductivit...mentioning

confidence: 99%

Quasi-two-dimensional organic superconductors: A review

Singleton¹,

Mielke²

2002

Contemporary Physics

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180

194

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Abstract. We present a review of quasi-two-dimensional organic superconductors. These systems exhibit many interesting phenomena, including reduced dimensionality, strong electron-electron and electron-phonon interactions and the proximity of antiferromagnetism, insulator states and superconductivity. Moreover, it has been possible to measure the electronic bands of many of the organics in great detail, in contrast to the situation in other well-known systems in which similar phenomena occur. We describe the crystal structure and normal-state properties of the organics, before presenting the experimental evidence for and against exotic superconductivity mediated by antiferromagnetic fluctuations. Finally, three instances of field-induced unconventional superconductivity will be described.

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Schramaet al.Reply:

Cited by 51 publications

References 13 publications

Strongly anisotropic s-wave gaps in exotic superconductors

Strongly anisotropic s-wave gaps in exotic superconductors

Organic Superconductors

Quasi-two-dimensional organic superconductors: A review

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