Phonon anomalies at the valence transition of SmS : An inelasticX-ray scattering study under pressure

TL;DR

This study investigates how phonon behaviors in SmS change under pressure during its valence transition, revealing softening of certain phonon modes that may facilitate pressure-induced superconductivity.

Contribution

It provides the first detailed inelastic x-ray scattering analysis of phonon dispersion in SmS across the valence transition under pressure.

Findings

Significant softening of longitudinal acoustic phonons along [111]

Stable phonon softening up to 80 kbar pressure

Conditions favorable for pressure-induced superconductivity

Abstract

The phonon dispersion curve of SmS under pressure was studied by inelastic x-ray scattering around the pressure-induced valence transition. A significant softening of the longitudinal acoustic modes propagating along the [111] direction was observed spanning a wide $q$ region from ($\frac{2\pi}{3a},\frac{2\pi}{3a},\frac{2\pi}{3a}$) up to the zone boundary as SmS becomes metallic. The largest softening occurs at the zone boundary and stays stable up to the highest measured pressure of 80 kbar while a gradual hardening of the low $q$ modes simultaneously appears. This phonon spectrum indicates favorable conditions for the emergence of pressure-induced superconductivity in SmS.