Pressure-induced shift of effective Ce valence, Fermi energy and phase boundaries in CeOs4Sb12

Abstract

CeOs _4 Sb _12 , a member of the skutterudite family, has an unusual semimetallic low-temperature $\mathcal{L}$ -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 $\mathcal{H}$ -phase and the $\mathcal{L}$ -phase is shifted to higher T by pressures of the order of 1 GPa, we observed only a marginal suppression of the $\mathcal{S}$ -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 $\mathcal{H}$ -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.

Keywords

• pressure
• valence transition
• CeOs4Sb12
• quantum oscillations
• quantum criticality