NMR Investigation of the Quasi One-dimensional Superconductor K$_{2}$Cr$_{3}$As$_{3}$

TL;DR

This study uses NMR to explore the magnetic fluctuations and unconventional superconductivity in the quasi one-dimensional superconductor K$_{2}$Cr$_{3}$As$_{3}$, revealing strong spin fluctuations and Luttinger liquid behavior.

Contribution

First NMR investigation revealing spin fluctuation enhancement and unconventional superconductivity in K$_{2}$Cr$_{3}$As$_{3}$, highlighting its Tomonaga-Luttinger liquid characteristics.

Findings

Strong enhancement of Cr spin fluctuations above T_c

Power law temperature dependence of 1/T_1T consistent with Luttinger liquid

Absence of Hebel-Slichter peak indicating unconventional superconductivity

Abstract

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