NMR Investigation of the Quasi-One-Dimensional SuperconductorK2Cr3As3

Abstract

We report ^{75}As NMR measurements on the new quasi-one-dimensional superconductor K_{2}Cr_{3}As_{3} (T_{c}∼6.1 K) [J. K. Bao et al., Phys. Rev. X 5, 011013 (2015)]. We found evidence for strong enhancement of Cr spin fluctuations above T_{c} in the [Cr_{3}As_{3}]_{∞} double-walled subnanotubes based on the nuclear spin-lattice relaxation rate 1/T_{1}. The power-law temperature dependence, 1/T_{1}T∼T^{-γ} (γ∼0.25), is consistent with the Tomonaga-Luttinger liquid. Moreover, absence of the Hebel-Slichter coherence peak of 1/T_{1} just below T_{c} suggests an unconventional nature of superconductivity.

Temperature and angular dependence of the upper critical field in K2Cr3As3

“…We argue that a dominant spintriplet pairing is more natural to meet the experimental data. Note that the spin-triplet pairing is consistent with the previous implications/suggestions in experimental and theoretical studies [14,15,[20][21][22][23][25][26][27]. We hope our result helps to find the exact superconducting order parameter in K 2 Cr 3 As 3 , which might expand the overall understanding of unconventional superconductivity.…”

“…(3) The 75 As nuclear quadrapole resonance (NQR) shows a strong enhancement of Cr-spin fluctuations above T c and, there is no Hebel-Slichter coherence peak in the temperature dependence of nuclear spinlattice relaxation rate just below T c for K 2 Cr 3 As 3 [20]. Similar result is given by the nuclear magnetic resonance (NMR) for Rb 2 Cr 3 As 3 , from which ferromagnetic spin fluctuations are additionally evidenced [21], supporting a spin-triplet pairing scenario.…”

Tripletpz-wave pairing in quasi-one-dimensionalA2Cr3As3superconductorsWu1, Yang2, Le3 et al. 2015Phys. Rev. B99101093View full textAdd to dashboardCite

“…The electronic structures calculated from Density Functional Theory (DFT) suggests that the 3d orbitals of Cr make major contribution near Fermi surfaces(FSs) 19,20 . The large electronic specific-heat coefficient 10 , the non-fermi liquid behavior in the normal state 10 and the abnormality in NMR relaxationrate 17 all suggest possible strong electron correlations in the family. The linearly temperature-dependent London penetration depth 18 , the lack of the Hebel-Slichter peak in NMR relaxation-rate upon the superconducting transition 17 , and the √ H-dependence of C v in the mixed state 11 suggest unconventional SC with line nodes in the system.…”

“…The large electronic specific-heat coefficient 10 , the non-fermi liquid behavior in the normal state 10 and the abnormality in NMR relaxationrate 17 all suggest possible strong electron correlations in the family. The linearly temperature-dependent London penetration depth 18 , the lack of the Hebel-Slichter peak in NMR relaxation-rate upon the superconducting transition 17 , and the √ H-dependence of C v in the mixed state 11 suggest unconventional SC with line nodes in the system. More importantly, the upper critical field largely exceeds the Pauli limit [10][11][12] , implying possible triplet pairings in the family.…”

Observation of a Raman-active phonon with Fano line shape in the quasi-one-dimensional superconductorK2Cr3As3

“…When the electron-phonon coupling is strong enough, the spectral lineshape of Raman phonon excitations is characterized by an asymmetric profile called Fano lineshape [1]. Despite a superconducting transition temperature (T c ) up to 6.1 K comparable to that of conventional superconductors, the recently discovered quasi-one-dimensional superconductors A 2 Cr 3 As 3 (A = K, Rb, Cs) have exotic properties that tentatively earned them the label of unconventional superconductors [2][3][4], such as an abnormal power law divergence of the 75 As nuclear spin lattice relaxation rate near T c [5]. Penetration depth measurements suggest a nodal line in the superconducting gap [6] and a large zero temperature upper critical field H c2 (0) compared to the Pauli limit has been attributed to a spin triplet p-wave pairing [2], in agreement with a theoretical study revealing strong ferromagnetic fluctuations caused by the frustration of Cr moments within one layer [7].…”