Discontinuous Transition from a Real Bound State to Virtual Bound State in a Mixed-Valence State of SmS

TL;DR

This paper investigates the pressure-induced transition in SmS from a mixed-valence, pseudogap state with local bound states to a metallic Kondo state, revealing a discontinuous phase change.

Contribution

It provides experimental evidence for a discontinuous transition from a real bound state to a virtual Kondo bound state in SmS under pressure.

Findings

Identification of a pseudogap caused by local spin singlet bound states.

Observation of a discontinuous transition at critical pressure P_c.

Transition from an insulating to a metallic, antiferromagnetic state.

Abstract

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.