Anisotropic superconducting gap probed by ${}^{125}$Te NMR in noncentrosymmetric Sc${}_{6}M$Te${}_2$ ($M$ = Fe, Co)

Abstract

The superconducting gap symmetry is investigated by ${}^{125}$Te NMR measurements on Sc${}_{6}M$Te${}_2$ ($M$ = Fe, Co) without spatial inversion symmetry. The spin susceptibility obtained from the Knight shift $K$ is suppressed below the superconducting transition temperature, while leaving a finite value down to the lowest temperature ($\simeq 0.4$ K). The nuclear spin-lattice relaxation rate $1/T_1$ follows a power law against temperature $T$ without showing a coherence peak characteristic of the isotropic gap. The result implies a pairing admixture or a residual density of states under magnetic field. The normal metallic state has a Korringa scaling relation between $1/T_{1}T$ and the Knight shift, reflecting a weak electron correlation.

7 pages, 7 figures

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