NMR Investigation of the Quasi-One-Dimensional Superconductor K2Cr3As3

We report As-75 NMR measurements on the new quasi-one-dimensional superconductor K2Cr3As3 (T-c similar to 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 [Cr3As3](infinity) double-walled subnanotubes based on the nuclear spin-lattice relaxation rate 1/T-1. The power-law temperature dependence, 1/T-1 T similar to T-gamma (gamma similar to 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.