Golden SmS is a paramagnetic, mixed-valence system with a pseudogap. With increasing pressure across a critical pressure Pc, the system undergoes a discontinuous transition into a metallic, anti-ferromagnetically ordered state. By using a combination of thermodynamic, transport, and magnetic measurements, we show that the pseudogap results from the formation of a local bound state with spin singlet. We further argue that the transition Pc is regarded as a transition from an insulating electron-hole gas to a Kondo metal, i.e., from a spatially bound state to a Kondo virtually bound state between 4f and conduction electrons.
@article{arxiv.1110.4427,
title = {Discontinuous Transition from a Real Bound State to Virtual Bound State in a Mixed-Valence State of SmS},
author = {Keiichiro Imura and Shinkichi Kanematsu and Kazuyuki Matsubayashi and Hiroyuki S. Suzuki and Kazuhiko Deguchi and Noriaki K. Sato},
journal= {arXiv preprint arXiv:1110.4427},
year = {2015}
}