Fermi-surface topologies and low-temperature phases of the filled Skutterudite compounds CeOs$_4$Sb$_{12}$ and NdOs$_4$Sb$_{12}$

TL;DR

This study investigates the Fermi surface topologies and low-temperature phases of CeOs$_4$Sb$_{12}$ and NdOs$_4$Sb$_{12}$ using high-field measurements, revealing distinct electronic behaviors and phase transitions related to their Fermi surfaces.

Contribution

The paper provides detailed Fermi surface mappings and identifies a field-induced transition in CeOs$_4$Sb$_{12}$, linking it to known Ce $ extit{ extalpha- extgamma}$ transitions, and compares NdOs$_4$Sb$_{12}$ to PrOs$_4$Sb$_{12}$.

Findings

NdOs$_4$Sb$_{12}$ has a Fermi surface similar to PrOs$_4$Sb$_{12}$ with smaller effective masses.

CeOs$_4$Sb$_{12}$ undergoes a field-induced transition from a semimetal to a state with a spherical Fermi surface.

The phase transition in CeOs$_4$Sb$_{12}$ is analogous to the $ extalpha- extgamma$ transition in Ce.

Abstract

MHz conductivity, torque magnetometer and magnetization measurements are reported on single crystals of CeOs$_4$Sb$_{12}$ and NdOs$_4$Sb$_{12}$ using temperatures down to 0.5~K and magnetic fields of up to 60~tesla. The field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas oscillations is deduced by rotating the samples about the $[010]$ and $[0\bar{1}1]$ directions. The results indicate that NdOs$_4$Sb$_{12}$ has a similar Fermi surface topology to that of the unusual superconductor PrOs$_4$Sb$_{12}$, but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of NdOs$_4$Sb$_{12}$. By contrast, CeOs$_4$Sb$_{12}$ undergoes a field-induced transition from an unusual semimetal into a high-field, high-temperature state characterized by a single, almost spherical Fermi-surface section. The behavior of the phase boundary and comparisons with models of the bandstructure lead us to propose that the field-induced phase transition in CeOs$_4$Sb$_{12}$ is similar in origin to the well-known $\alpha-\gamma$ transition in Ce and its alloys.