NMR study of black-phase in SmS

We report the result of the ³³S nuclear magnetic resonance (NMR) measurement on the nonmagnetic semiconductor SmS at ambient pressure. For this measurement, the ³³S isotope enriched powder sample of SmS was prepared to increase the ³³S NMR intensity. We have attempted ³³S NMR measurement on SmS and successfully observed the signal of it. With decreasing temperature, the spectrum measured at the constant magnetic field shifted to lower frequency and became weakly temperature dependent below 50 K. The presence of the energy gap was microscopically established by the rapid decrease in the nuclear spin-lattice relaxation rate 1/T₁. The activation energy was deduced to be 625 K from an Arrhenius plot of T₁