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Skinta, John A.; Kim, Mun-Seog; Lemberger, Thomas R.; Greibe, Tine; Naito, Makio

doi:10.1103/physrevlett.88.207005

Cited by 131 publications

(66 citation statements)

References 21 publications

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“…However, this has been contrasted by tunnelling [12,13] and some other specific heat [14] and penetration depth measurements [15,16,17]. In particular, there may be a crossover from d-wave to s-wave symmetries by changing the doped electron concentration [18,19] or decreasing temperature [20]. Although such a crossover may explain the conflicting experimental results on the pairing symmetry in the electron-doped cuprates, the characteristics of such possible s-wave pairing symmetry has yet to be established.…”

Section: Introductionmentioning

confidence: 82%

Distinct pairing symmetries inNd1.85Ce0.15CuO4−yandLa1.89

et al. 2005

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We used point-contact tunnelling spectroscopy to study the superconducting pairing symmetry of electron-doped N d1.85Ce0.15CuO4−y (NCCO) and hole-doped La1.89Sr0.11CuO4 (LSCO). Nearly identical spectra without zero bias conductance peak (ZBCP) were obtained on the (110) and (100) oriented surfaces (the so-called nodal and anti-nodal directions) of NCCO. In contrast, LSCO showed a remarkable ZBCP in the nodal direction as expected from a d-wave superconductor. Detailed analysis reveals an s-wave component in the pairing symmetry of the NCCO sample with ∆/kBTc = 1.66, a value remarkable close to that of a weakly coupled BCS superconductor. We argue that this s-wave component is formed at the Fermi surface pockets centered at (±π,0) and (0,±π) although a d-wave component may also exist.

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Section: Introductionmentioning

confidence: 82%

Distinct pairing symmetries inNd1.85Ce0.15CuO4−yandLa1.89

et al. 2005

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“…We also note that throughout the exotics this synergy is consistent with the considerable deviations from a strict T c µ et al 2002). Other data shows nodes for underdoped films together with the absence of nodes for overdoped films of this material, and likewise for the lanthanum analog of this material (Biswas et al 2002, Skinta et al 2002b see also Zheng et al 2002).But instead of characterizing the latter electron-doped cuprate results as "a d to s transition", as in these papers, it is far more straightforward and therefore more reasonable to interpret this as simply a change in the degree of anisotropy within the swave gap form of Eq. (1).…”

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confidence: 80%

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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“…Pairing symmetry of electron-doped high-T c cuprate superconductors such as Nd 2−x Ce x CuO 4 and Pr 2−x Ce x CuO 4 is a long standing problem [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Although no consensus has been reached yet, more and more recent experimental results have suggested that the order parameter of electron-doped cuprates is likely to have d x 2 −y 2 -wave pairing symmetry [1,2,3,5,9,10,14,16,17], in close resemblance to that of hole-doped materials.…”

Section: Introductionmentioning

confidence: 99%

Two-band model of Raman scattering on electron-doped high-Tcsuperconductors

Liu

Luo

et al. 2006

Phys. Rev. B

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We have analyzed the B1g and B2g Raman spectra of electron-doped cuprate superconductors Nd2−xCexCuO4 and Pr2−xCexCuO4 using a weakly coupled two-band model. One of these two bands is centered around (±π/2, ±π/2) and couples more strongly with the B2g mode, while the other is centered around (±π, 0) and (0, ±π) and couples more strongly with the B1g mode. This model explains in a natural way why the B2g Raman peak occurs at a higher frequency than the B1g one at optimal doping, and how these two peaks change with doping in agreement with experiments. The result thus supports that there are two kinds of quasiparticles in electron-doped cuprates and d x 2 −y 2 -wave superconductivity is driven by the holelike band and a proximity effect on the electronlike band.

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Evidence for a Transition in the Pairing Symmetry of the Electron-Doped CupratesLa2−xCex

Cited by 131 publications

References 21 publications

Distinct pairing symmetries inNd1.85Ce0.15CuO4−yandLa1.89

Distinct pairing symmetries inNd1.85Ce0.15CuO4−yandLa1.89

Strongly anisotropic s-wave gaps in exotic superconductors

Two-band model of Raman scattering on electron-doped high-Tcsuperconductors

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