NMR characteristics in noncentrosymmetric Mo ₃Al ₂C

We present an extensive study of the noncentrosymmetric superconductor Mo ₃Al ₂C using 27Al nuclear magnetic resonance (NMR) spectroscopy. The NMR line shapes, Knight shifts, as well as spin-lattice relaxation rates in both superconducting and normal states have been identified. In the superconducting phase, the results of the Knight shift and relaxation rate signify the existence of finite density of states, attributed to the strong antisymmetric spin-orbital coupling effect enhanced by intrinsic defects. In the normal state, peculiar changes such as the broadening of the NMR linewidth and the distinct drop of the Knight shift were discerned across a characteristic temperature of T ^*196 K. Moreover, the magnitude of 1/T ₁T decreases markedly and develops pseudogaplike behavior below T ^*. We associated these anomalous features with distortions near the Al sites toward a lower symmetric structural environment, leading to the modification of electronic structures around Fermi surfaces.