NMR/NQR and AC-susceptibility Studies in the Weyl Semimetal Superconductor 1T-MoTe 2 under Pressure

We performed the Te-nuclear magnetic resonance, the Mo-nuclear quadrupole resonance, and the AC susceptibility in the Weyl semimetal superconductor 1T-MoTe2 at pressures up to 2.17GPa. From the temperature and pressure dependence of the AC susceptibility, the superconducting transition temperature Tc and the upper critical field Hc2 were estimated. The results deviate from the Werthamer–Helfand–Hohenberg model but are well described by Hc2(T) = Hc2(0)[1 − T=Tc]α. The latter fit yields Hc2(0) = 1.50T, Tc = 3.81K, and α = 1.1 at 2.17GPa, suggesting that the superconductivity lies in a strong-coupling regime. Since the nuclear spin–lattice relaxation rate divided by temperature, 1=T1T, follows the Korringa relation at ambient pressure, the increase in 1=T1T with pressure up to approximately 0.7GPa indicates an increase in the density of states (DOS), N(EF). This trend mirrors the pressure dependence of Tc in the low-pressure region, consistent with the BCS mechanism. Above 0.7GPa, however, N(EF) slightly decreases while Tc continues to rise, suggesting an additional pairing contribution beyond the conventional BCS picture. In the 1TA phase at 2.17GPa, the absence of a coherence peak in 1=T1T around Tc, accompanied by a two-step decrease just below Tc, was observed, which may be a signature of unconventional superconductivity. 1. Introduction.