Unique Band Structure of Pressure Induced Semiconducting State in SmS Characterized by 33S-Nuclear Magnetic Resonance Measurements

In Kondo insulators, where a small energy gap evolves only at low temperatures, it is challenging to experimentally clarify their electronic structures, especially under high pressure. In this study, we have carried out high-pressure ³³S-nuclear magnetic resonance measurements on a pressure-induced semiconducting phase with a small energy gap of SmS. To analyze the recovery curve of nuclear spin–lattice relaxation time T₁, consisting of multiple components, the Bayesian inference was introduced. The unique temperature dependence of 1/T₁ is reproduced based on a simplified rectangular band model and a periodic Anderson model, which allows to obtain parameters characterizing the semiconducting state semi-quantitatively: the bandwidths of conduction electrons and quasiparticles are much narrower and the energy gap is smaller than for SmB₆, a prototypical Kondo insulator. This peculiar band structure in the small gap state may arise from the characteristics of weak correlations and relatively strong hybridization.