Normal and Superconducting Properties of the Noncentrosymmetric Mo3Al2C

Abstract

We have investigated the noncentrosymmetric superconductor Mo3Al2C prepared by spark plasma sintering, in which the amount of impurity phase was considerably reduced. Another phase transition in the normal state was clearly observed in the spark plasma sintered sample as an abrupt change in the 27Al nuclear magnetic resonance (NMR) spectra and an anomaly in the electrical resistivity. In the transition, a partial gap opening on the Fermi surface is inferred from the decrease in the nuclear spin–lattice relaxation rate \(1/T_{1}\) and the magnetic susceptibility χ below 200 K. The simultaneous presence of two components in the NMR spectra and thermal hysteresis in χ at \({\sim}200\) K indicates the first-order character of the transition. These results imply the formation of the charge-density wave state in Mo3Al2C. In the superconducting state, \(1/T_{1}\) shows a peak just below \(T_{\text{c}}\) and decreases exponentially with temperature, in good agreement with that is expected for the \(s\)-wave super...