Infrared properties of exotic superconductors

Timusk, T.

doi:10.1016/s0921-4534(99)00042-8

Cited by 39 publications

(2 citation statements)

References 58 publications

(67 reference statements)

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“…Tunnelling data have shown very good agreement with BCS (isotropic gap) modelling (Sato et al 1990, Huang et al 1990, Sharifi et al 1991, Zasadzinski et al 1991, Kussmaul et al 1993, Kosugi et al 1994). The T << T c data for penetration depth (Pambianchi et al 1994) and specific heat (Woodfield et al 1999) show isotropic-gap behavior, and the optical conductivity of BKBO also looks quite conventional (Puchkov et al 1994, Timusk 1999. BKBO thus appears "anomalously conventional" in this respect.…”

Section: Bkbomentioning

confidence: 94%

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: Bkbomentioning

confidence: 94%

Strongly anisotropic s-wave gaps in exotic superconductors

Brandow

2003

Philosophical Magazine

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“…Due to the ambient pressure superconductivity (TMTSF) 2 ClO 4 has drawn most attention starting from the early days [60,[102][103][104] until the nice reviews of Timusk in the 1990s [80,105,106]. In order to allow the anions to order near 24 K, the sample has to be cooled down very slowly through T AO ; only then the metallic state is preserved and superconductivity reached at T c = 1.2 K. Fast cooling results in the insulating spin-density-wave ground state (Figure 7(b)0.…”

Section: Very Low-frequency Behaviormentioning

confidence: 99%

Electrodynamics of Bechgaard Salts: Optical Properties of One-Dimensional Metals

Dressel

2012

ISRN Condensed Matter Physics

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The electrodynamic properties of the quasi-one-dimensional organic conductors (TMTSF)2X are discussed, with particular emphasis on important deviations from the simple Drude model, the transition from a Luttinger-liquid to a Fermi-liquid behavior at the dimensional crossover when pressure is applied or temperature reduced, indications of a pseudogap as well as a low-frequency collective mode. Superconductivity and spin-density-wave ground states breaking the symmetry and gaps should occur in the excitation spectra. The previous literature is summarized and the current status of our understanding presented. Novel THz experiments on (TMTSF)2PF6 and (TMTSF)2ClO4 not only shine light into some of the open questions, but also pose new ones.

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Pair-Transfer Superconductivity on Doping Determined Bands and the Pseudogap

Kristoffel

Rubin

2002

New Trends in Superconductivity

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Infrared properties of exotic superconductors

Cited by 39 publications

References 58 publications

Strongly anisotropic s-wave gaps in exotic superconductors

Strongly anisotropic s-wave gaps in exotic superconductors

Electrodynamics of Bechgaard Salts: Optical Properties of One-Dimensional Metals

Pair-Transfer Superconductivity on Doping Determined Bands and the Pseudogap

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