Multigap Superconductivity in Y2C3: A 13C-NMR Study

Harada, Atsushi; Akutagawa, Satoshi; Miyamichi, Y.; Mukuda, H.; Kitaoka, Y.; Akimitsu, Jun

doi:10.1143/jpsj.76.023704

Cited by 41 publications

(53 citation statements)

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“…2, particularly in the high temperature region near T c . Such a fitting gives the following parameters: 2∆ 1 /k B T c = 4.9, 2∆ 2 /k B T c = 1.1 and x = 0.86, which are in good agreement with those in NMR [23] and µSR measurements [24]. However, significant deviation of ρ s (T ) from the two-gap model is observed at temperatures below 0.4T c (see inset (a) in Fig.…”

supporting

confidence: 81%

“…While there is some variation among the weights reported, the fits near T c all give a dominant large gap of 2∆ 1 /k B T c ≈ 5 and a small gap of 2∆ 2 /k B T c ≈ 1.1-2. On the other hand, the Knight shift in NMR decreases to approximately 2/3 of its normal-state value, and the temperature dependence of 1/T 1 deviates from the predictions of a conventional BCS model [23]. Recently, we noticed that Y 2 C 3 shows a high upper critical field (µ 0 H c2 (0) ≃ 29T), which might indicate the impor-…”

mentioning

confidence: 87%

“…A two-gap scenario, as previously discussed in MgB 2 [27,28], has been proposed to describe the NMR and µSR data for Y 2 C 3 [23,24]. Here we tried to fit ρ s (T ) with a two-gap BCS model: ρ s (T ) = xδρ s (∆ 1 (0), T ) + (1 − x)δρ s (∆ 2 (0), T ), where ∆ i (i = 1 and 2) are the energy gaps at T = 0 and x is the relative weight for the ∆ 1 .…”

mentioning

confidence: 99%

“…Thus it might provide another example in which to study the effect of ASOC on superconductivity. Measurements of nuclear-magnetic-resonance (NMR) [23] and muon spin relaxation (µSR) [24] indicate a complex gap structure in Y 2 C 3 which cannot be described in terms of a simple s-wave or a d-wave gap function, but can be qualitatively fitted with a two-gap model at temperatures near T c . While there is some variation among the weights reported, the fits near T c all give a dominant large gap of 2∆ 1 /k B T c ≈ 5 and a small gap of 2∆ 2 /k B T c ≈ 1.1-2.…”

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Evidence of nodal gap structure in the noncentrosymmetric superconductorY2C3

et al. 2011

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The magnetic penetration depth λ(T ) and the upper critical field µ0Hc2(Tc) of the noncentrosymmetric (NCS) superconductor Y2C3 have been measured using a tunnel-diode (TDO) based resonant oscillation technique. We found that the penetration depth λ(T ) and its corresponding superfluid density ρs(T ) show linear temperature dependence at very low temperatures (T ≪ Tc), indicating the existence of line nodes in the superconducting energy gap. Moreover, the upper critical field µ0Hc2(Tc) presents an upturn at low temperatures with a rather high value of µ0Hc2(0) ≃ 29T, which slightly exceeds the weak-coupling Pauli limit. We discuss the possible origins for these nontrivial superconducting properties, and argue that the nodal gap structure in Y2C3 is likely attributed to the absence of inversion symmetry, which allows the admixture of spin-singlet and spin-triplet pairing states. The symmetries of a superconductor, e.g., timereversal and spatial inversion symmetries, may impose important constraints on the pairing states. Among the previously investigated superconductors, most possess an inversion center in their crystal structures, in which the Cooper pairs are either in an even-parity spin-singlet or odd-parity spin-triplet pairing state, according to the Pauli principle and parity conservation [1,2]. However, the tie between spatial symmetry and the Cooper-pair spins might be violated in a superconductor lacking inversion symmetry [3][4][5][6][7]. In these materials, an asymmetric potential gradient yields an antisymmetric spin-orbit coupling (ASOC), which splits the Fermi surface into two spin-ordered subsurfaces, with pairing allowed both across one subsurface and between the two. ASOC splits the degeneracy of conduction electron, and allows the admixture of spin-singlet and spin-triplet pairing states within the same orbital channel. Various exotic electromagnetic properties may arise in the parity-violated materials [3][4][5][6][7].Until now, only a very few non-centrosymmetric (NCS) superconductors have been investigated. In the heavy fermion NCS superconductors, e.g., CePt 3 Si and CeMSi 3 (M=Rh, Ir), the upper critical field is greatly enhanced in comparison with that of other heavy fermion materials [8][9][10], exceeding the Pauli limit in a weak coupling BCS model. Measurements of thermodynamic properties in CePt 3 Si indicated the existence of line nodes in the superconducting gap, even though a weak Hebel-Slichter coherence peak is observed below T c [11][12][13][14]. These unconventional features were interpreted in terms of a Rashbatype spin-orbit coupling model arising from the absence of inversion symmetry [5][6][7]. However, the strong electronic correlations and the closeness to a magnetic instability might complicate the analysis of the ASOC effect on superconductivity. Recent work on Li 2 (Pd 1−x Pt x ) 3 B systems demonstrated that spin-singlet and spin-triplet order parameters can add constructively and destructively, leading to two different gap functions and the possible occurrence of acc...

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confidence: 81%

mentioning

confidence: 87%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Evidence of nodal gap structure in the noncentrosymmetric superconductorY2C3

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“…As a consequence of inversion symmetry breaking, exotic properties have been predicted and observed, such as multigap and nodal superconductivity [8][9][10][11], large upper critical fields [12][13][14], nontrivial quantum topology in the superconducting ground state [15], as well as charge and spin currents along the edge [16]. The understanding of the nature of the pairing and the mechanisms that lead to superconductivity in materials without inversion symmetry is thus a fundamental and highly debated issue in the field of unconventional superconductors.…”

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Evidence of double-gap superconductivity in noncentrosymmetricNb0.18Re0.82single crystals

et al. 2015

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Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. We combine point contact spectroscopy with specific heat measurements to probe the superconducting state in noncentrosymmetric Nb 0.18 Re 0.82 single crystals. The conductance spectra clearly exhibit a two-peak structure that is well reproduced within a two-band model with isotropic gaps in the spectrum. Such an observation is confirmed by distinct features of the specific heat both at low temperatures and in the range approaching the transition to the normal state. The analyses provide convincing evidence that the two-gap superconducting pairing is a robust feature of Nb 0.18 Re 0.82 .

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Carbon Based Superconductors

Kremer

Kim

Simon

2007

High Tc Superconductors and Related Transition Metal Oxides

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We review the characteristics of some carbon based novel superconductors which emerged in the past two decades since the discovery of superconductivity in the high-T c oxocuprates. In particular, we summarize the properties of ternary layered carbide halides of the rare rarth metals with composition RE 2 C 2 X 2 (RE = Y, La; X=Cl, Br, I) and of the rare earth di-and sesquicarbides, YC 2 , LaC 2 and La 2 C 3 . Finally, we briefly discuss the properties of the recently discovered Ca and Yb intercalated graphite superconductors, CaC 6 and YbC 6 . PACS numbers: abc 1 I. INTRODUCTIONThe discovery of high-T c superconductivity by Bednorz and Müller 1 in 1986 marks the beginning of a period of a vivid search for -chemically and physically partly extremely complex -new oxocuprates and for theoretical approaches to understand their puzzling properties, quite a few of which remained controversial even until today. The advent of this completely unexpected class of new superconductors also revived the interest in more conventional -'low-T c ' -superconductors. In due course, a number of new systems were found, and already known superconductors were reinvestigated with improved and refined experimental and theoretical tools. These activities led to surprising new discoveries as that of the 40 K superconductor MgB 2 by Nagamatsu et al. 2 Apart from its T c , MgB 2 is special primarily for two reasons: Compared e.g. to the high-T c oxocuprates its crystal structure is of remarkable simplicity allowing electronic and phononic structure calculations of high precision, and MgB 2 is the first system for which multigap superconductivity has independently been evidenced by several experimental techniques. 3,4,5 Until the discovery of MgB 2 , doped fullerenes had shown the highest T c values after the high-T c oxocuprates. With large enough quantities of purified C 60 available, 6 Hebard et al. prepared superconductors with a T c of 18 K by doping polycrystalline C 60 and C 60 films with alkali metals. 7 Subsequently, by adjusting the separation of the C 60 molecules using a proper composition of different alkali metals, T c 's up to ∼33 K were reached. 8 Superconductivity in doped fullerenes also redraw attention to carbon based superconductors in general. Especially, binary and quasibinary transition metal carbides have a long history in showing T c 's which were among the highest found before the discovery of the high-T c oxocuprates. 9 Later borocarbides of composition REM 2 B 2 C, with RE = Y or Lu and M = Ni or Pd, with T c 's up to 22 K attracted considerable interest. 10,11 Superconductivity in graphite intercalation compounds (GICs) is another early field of research which recently was revived. The discovery of superconducting GICs dates back to the pioneering work of Bernd Matthias' group in the 1960's, however, the T c 's of these early GICs remained well below 1 K. 12,13 Subsequently, the T c 's of alkali metal intercalated GICs could be raised by intercalation under pressure with e.g. Li and Na, but T c did not signifi...

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Multigap Superconductivity in Y₂C₃: A ¹³C-NMR Study

Cited by 41 publications

References 11 publications

Evidence of nodal gap structure in the noncentrosymmetric superconductorY2C3

Evidence of nodal gap structure in the noncentrosymmetric superconductorY2C3

Evidence of double-gap superconductivity in noncentrosymmetricNb0.18Re0.82single crystals

Carbon Based Superconductors

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