Nuclear Spin Relaxation in Normal and Superconducting Aluminum

Hebel, L. C.; Slichter, Charles P.

doi:10.1103/physrev.113.1504

Cited by 655 publications

(257 citation statements)

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“…We note that the magnetization recovery did not follow a simple exponential law in the SC state, rather a stretched exponential behavior indicating a distribution of relaxation times [20], likely due to misaligned crystallites and the vortex state. The T 2 behavior is indeterminate as to the orbital structure of the Cooper pairs, however the salient features are that 1/T 1 decreases as a power law and there is no evidence of a Hebel-Slichter coherence peak [21]. With these factors considered, it is likely that U 2 PtC 2 does not have a fully gapped Fermi surface, rather a nodal structure, the details of which may become more clear from measurements on single crystals.…”

mentioning

confidence: 95%

Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples Using
Mounce
¹
,
Yaśuoka
²
,
Koutroulakis
³

et al. 2015
Phys. Rev. Lett.
5
1
3
0
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Nuclear magnetic resonance (NMR) measurements on the 195 Pt nucleus in an aligned powder of the moderately heavy-fermion material U2PtC2 are consistent with spin-triplet pairing in its superconducting state. Across the superconducting transition temperature and to much lower temperatures, the NMR Knight shift is temperature independent for field both parallel and perpendicular to the tetragonal c-axis, expected for triplet equal-spin pairing superconductivity. The NMR spin-lattice relaxation rate 1/T1, in the normal state, exhibits characteristics of ferromagnetic fluctuations, compatible with an enhanced Wilson ratio. In the superconducting state, 1/T1 follows a power law with temperature without a coherence peak giving additional support that U2PtC2 is an unconventional superconductor. Bulk measurements of the AC-susceptibility and resistivity indicate that the upper critical field exceeds the Pauli limiting field for spin-singlet pairing and is near the orbital limiting field, an additional indication for spin-triplet pairing.

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mentioning

confidence: 95%

Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples Using
Mounce
¹
,
Yaśuoka
²
,
Koutroulakis
³

et al. 2015
Phys. Rev. Lett.
5
1
3
0
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“…The NMR rate in the presence of a spin-singlet swave superconducting state is enhanced just below a critical temperature T c , owing to the coherence factor [23]. This coherence peak (Hebel-Slichter peak) [24,25] comes from the formation of superconducting gaps. The absence of the peak and a power-law behavior of T −1 1 at low temperatures indicate the occurrence of unconventional states [26][27][28].…”

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confidence: 99%

Inverse coherence effects in nuclear magnetic relaxation rates as a sign of topological superconductivity

2015

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We reveal that three-dimensional multi-orbital topological superconductivity can be identified by a bulk measurement, i.e., the temperature dependence of nuclear magnetic relaxation (NMR) rates. Below a critical temperature Tc, the NMR rate in the topological state exhibits an anti-peak profile, which is opposite to the conventional s-wave state. This inversion coherence effect comes from a twist of order parameters with respect to orbital and spin degrees of freedom. Our self-consistent calculations in the model for CuxBi2Se3 prove that the inverse coherence effect appears as a concave temperature dependence of the NMR rates. We propose that a time-reversal-invariant orbitalsinglet spin-triplet topological superconductivity is characterized by the temperature dependence of the NMR rate. [17][18][19]. Among these studies, although the gapless bound states on surfaces at low temperatures are actively studied [9,11,[20][21][22], observing an intrinsic behavior via bulk measurements is rarely argued. In addition, the setups of surface measurements would be sensitively affected by the characteristics of the interfaces between materials and probes. Thus, a bulk measurement sensitive to topological characters is important for supporting results in surface measurements and revealing the properties of Cooper-pair condensations.A key quantity of connecting topological characters with bulk measurements is a correlation function. Current-current correlation functions, for example, lead to the quantized conductance in integer quantum Hall effects [5]. Spin-spin correlation functions are essential for superconductivity since these quantities well reflect the spin-state properties of Cooper pairs. Nuclear magnetic relaxation (NMR) rates (T −1 1 ) are directly related to the spin-spin correlation functions. Therefore, it is interesting and important question to ask whether NMR rates contain any characteristic information on topological superconductivity. Specifically, the coherence effect is notable. The NMR rate in the presence of a spin-singlet swave superconducting state is enhanced just below a critical temperature T c , owing to the coherence factor [23]. This coherence peak (Hebel-Slichter peak) [24,25] comes from the formation of superconducting gaps. The absence of the peak and a power-law behavior of T −1 1 at low temperatures indicate the occurrence of unconventional states [26][27][28].In this paper we claim that the bulk measurements of NMR rates detect a 3D odd-parity fully-gapped topological superconducting state in time-reversal-invariant multi-orbital systems. An inverse coherence effect just below T c is the signature of this odd-parity state; the coherence factor contributes to the NMR rates with an opposite sign to that of the conventional s-wave states. Our self-consistent calculations in the model of Cu x Bi 2 Se 3 [13] show that this sign reversal leads to an anti-peak behavior of the NMR rates below T c . Using the Fermion anticommutation property, we show that the odd parity allows a twist of a gap fun...

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“…Historically, nuclear magnetic resonance (NMR) studies showing up the so called Hebel-Slichter peak in the nuclear spin-lattice relaxation rate (NSLRR) played a significant role in establishing the BCS theory as the first microscopic description of conventional (weakly coupled) superconductors. 2 Physically, this behavior is caused by the coherence factors and the symmetry of a single nodeless superconducting (SC) gap. 3 Nowadays, within a simplified approach (ignoring damping, strong coupling, anisotropy, impurity, and inhomogeneity effects 4,5 ) its presence or absence together with the T -dependence of the NSLRR, 1/T 1 , below T c are frequently used to discriminate tentatively conventional from unconventional pairing.…”

mentioning

confidence: 99%

Unusual disorder effects in superconductingLaFeAs1−δO0.9F0.1as revealed by
Hammerath
¹
,
Drechsler
²
,
Grafe
³

et al. 2010
Phys. Rev. B

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We report 75 As NMR measurements of the spin-lattice relaxation in the superconducting state of LaFeAsO0.9F0.1 and As-deficient LaFeAs 1−δ O0.9F0.1. The temperature behavior of 1/T1 below Tc changes drastically from a T 3 -dependence for LaFeAsO0.9F0.1 to a T 5 -dependence for the Asdeficient sample. These results, together with the previously reported unexpected increase of Tc and the slope of the upper critical field near Tc for the As-deficient sample, are discussed in terms of non-universal SC gaps in Fe-pnictides and the effect of As deficiency as an exotic case where nonmagnetic 'smart' impurities even stabilize an s±−wave superconductor or within a scenario of a disorder-driven change to s++-superconductivity.PACS numbers: 74.70. Xa, 74.20.Rp The symmetry of the order parameter and the underlying Cooper-pairing mechanism in the newly discovered Fe-based superconductors 1 are one of the most challenging problems in contemporary solid state physics. Historically, nuclear magnetic resonance (NMR) studies showing up the so called Hebel-Slichter peak in the nuclear spin-lattice relaxation rate (NSLRR) played a significant role in establishing the BCS theory as the first microscopic description of conventional (weakly coupled) superconductors. 2 Physically, this behavior is caused by the coherence factors and the symmetry of a single nodeless superconducting (SC) gap. 3 Nowadays, within a simplified approach (ignoring damping, strong coupling, anisotropy, impurity, and inhomogeneity effects 4,5 ) its presence or absence together with the T -dependence of the NSLRR, 1/T 1 , below T c are frequently used to discriminate tentatively conventional from unconventional pairing. For a single Fermi surface (FS) sheet and superconductivity in the clean limit T 3 -and T 5 -dependencies would be regarded as evidence for line-and point-node SC order parameters, respectively, which for singlet pairing correspond to the d-and a special s + g-wave state. Recently it has been realized that the situation in multibands and especially in Fe-pnictides with impurities is far from being that simple, in particular, there is no universal behavior for the growing number of related compounds. 6 The s ± -scenario proposed 7-10 at the early stages of the Fe-pnictide research at present is still the most popular one. Due to the vicinity of a competing spin density wave state in the phase diagram, it is tempting to assume that antiferromagnetic (AFM) spin fluctuations might be the dominant pairing glue. Then, from the FS topology given by small hole (electron) pockets centered * Present address: Department of Physics, University of Florida, Gainesville,Florida 32611, USA around the Γ = (0, 0) (M = (π, π))-points of the Brillouin zone, a nodeless gap with opposite signs on each of the disconnected FS pockets separated by the wave vector Q = (π, π) is naturally suggested.With respect to pair-breaking interband impurity scattering some doubts about this sign-reversed s ± -scenario have been put forward. 11-17 Also the available weak couplin...

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Nuclear Spin Relaxation in Normal and Superconducting Aluminum

Cited by 655 publications

References 23 publications

Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples Using
Mounce
¹
,
Yaśuoka
²
,
Koutroulakis
³

et al. 2015
Phys. Rev. Lett.
5
1
3
0
View full text Add to dashboard Cite

Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples Using
Mounce
¹
,
Yaśuoka
²
,
Koutroulakis
³

et al. 2015
Phys. Rev. Lett.
5
1
3
0
View full text Add to dashboard Cite

Inverse coherence effects in nuclear magnetic relaxation rates as a sign of topological superconductivity

Unusual disorder effects in superconductingLaFeAs1−δO0.9F0.1as revealed by
Hammerath
¹
,
Drechsler
²
,
Grafe
³

et al. 2010
Phys. Rev. B

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Nuclear Spin Relaxation in Normal and Superconducting Aluminum

Cited by 655 publications

References 23 publications

Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples UsingMounce1, Yaśuoka2, Koutroulakis3 et al. 2015Phys. Rev. Lett.5130View full textAdd to dashboardCite

Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples UsingMounce1, Yaśuoka2, Koutroulakis3 et al. 2015Phys. Rev. Lett.5130View full textAdd to dashboardCite

Inverse coherence effects in nuclear magnetic relaxation rates as a sign of topological superconductivity

Unusual disorder effects in superconductingLaFeAs1−δO0.9F0.1as revealed byHammerath1, Drechsler2, Grafe3 et al. 2010Phys. Rev. B

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Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples Using
Mounce
¹
,
Yaśuoka
²
,
Koutroulakis
³

et al. 2015
Phys. Rev. Lett.
5
1
3
0
View full text Add to dashboard Cite

Detection of a Spin-Triplet Superconducting Phase in Oriented PolycrystallineU2PtC2Samples Using
Mounce
¹
,
Yaśuoka
²
,
Koutroulakis
³

et al. 2015
Phys. Rev. Lett.
5
1
3
0
View full text Add to dashboard Cite

Unusual disorder effects in superconductingLaFeAs1−δO0.9F0.1as revealed by
Hammerath
¹
,
Drechsler
²
,
Grafe
³

et al. 2010
Phys. Rev. B