Pressure-induced shift of effective Ce valence, Fermi energy and phase boundaries in CeOs$_4$Sb$_{12}$

TL;DR

This study investigates how pressure influences the electronic phases, Fermi surface, and valence states of CeOs$_4$Sb$_{12}$, revealing shifts in phase boundaries and unexpected changes in electronic structure under high magnetic fields.

Contribution

It provides new insights into pressure effects on CeOs$_4$Sb$_{12}$'s phase diagram, Fermi surface, and valence, with detailed measurements up to 3 GPa and 41 T.

Findings

High-temperature valence transition shifts to higher T with pressure.

Fermi surface size decreases with increasing pressure.

Pressure has limited effect on low-temperature $ ext{S}$-phase properties.

Abstract

CeOs$_4$Sb$_{12}$, a member of the skutterudite family, has an unusual semimetallic low-temperature $\cal{L}$-phase that inhabits a wedge-like area of the field $H$ - temperature $T$ phase diagram. We have conducted measurements of electrical transport and megahertz conductivity on CeOs$_4$Sb$_{12}$ single crystals under pressures of up to 3 GPa and in high magnetic fields of up to 41 T to investigate the influence of pressure on the different $H$-$T$ phase boundaries. While the high-temperature valence transition between the metallic $\cal{H}$-phase and the $\cal{L}$-phase is shifted to higher $T$ by pressures of the order of 1 GPa, we observed only a marginal suppression of the $\cal{S}$-phase that is found below 1 K for pressures of up to 1.91 GPa. High-field quantum oscillations have been observed for pressures up to 3.0 GPa and the Fermi surface of the high-field side of the $\cal{H}$-phase is found to show a surprising decrease in size with increasing pressure, implying a change in electronic structure rather than a mere contraction of lattice parameters. We evaluate the field-dependence of the effective masses for different pressures and also reflect on the sample dependence of some of the properties of CeOs$_4$Sb$_{12}$ which appears to be limited to the low-field region.