Fermi-surface topologies and low-temperature phases of the filled skutterudite compoundsCeOs4Sb12andNdOs4Sb12

Abstract

MHz conductivity, torque magnetometer and magnetization measurements are reported on single crystals of CeOs4Sb12 and NdOs4Sb12 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 [011] directions. The results indicate that NdOs4Sb12 has a similar Fermi surface topology to that of the unusual superconductor PrOs4Sb12, but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of NdOs4Sb12. By contrast, CeOs4Sb12 undergoes a field-induced transition from an unusual semimetal into a high-field, hightemperature 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 CeOs4Sb12 is similar in origin to the well-known α − γ transition in Ce and its alloys.

Unusual phase boundary of the magnetic-field-tuned valence transition inCeOs4Sb12

“…By contrast, we show here that the valence transition in CeOs 4 Sb 12 , identified by its effect on the Fermi surface and material properties [1], does not follow the above textbook elliptical behavior. We performed MHz conductivity, magnetostriction and resistivity measurements on CeOs 4 Sb 12 , to map out the phase diagram shown in Fig 1 . The valence transition separates the low-T , low-H, semimetallic L phase and the high-T , high-H, metallic H phase [1]; it is immediately obvious that it behaves very unconventionally, falling back to lower T as H → 0 and lower H as T → 0. We suggest that this unusual behavior is due to a sensitivity of the low-temperature groundstates of CeOs 4 Sb 12 to quantum fluctuations, and to a proximity to a topological semimetallic phase.…”

“…CeOs 4 Sb 12 is part of an interesting series of rareearth-based filled skutterudites that includes the unconventional superconductor PrOs 4 Sb 12 [12,13] and [9,[15][16][17] to the H−phase, characterized by a simple, almost spherical Fermi surface with a light effective mass [1]. Band structure calculations for the L-phase confirm the gapless ground state and predict the system to become a topological semimetal or topological Kondo insulator under applied strain [16,17].…”

“…Valence transitions, in which f -electrons undergo a temperature and/or magnetic-field driven transformation from itinerant to quasi-localized, are associated with significant changes in material properties [1][2][3] and dramatic alterations to the Fermi surface [1,4]. Perhaps the bestknown is the γ − α transition in Ce and its alloys, which leads to a spectacular volume collapse of the sample [2,3].…”

“…In Ref. [1], an attempt to trace the high-temperature limits of the L − H boundary was made using χ = ∂M/∂H contours, where M is the magnetization; however, subsequent experiments suggested that χ was not an accurate indicator of the (H, T ) position of the valence transition, prompting the current comprehensive series of measurements that reveal the much more unusual behavior shown in Fig. 1.…”

“…CeOs 4 Sb 12 single crystals were prepared using a molten-flux technique [15] with an excess of Sb. Further details can be found in [1]. Several single crystals (cubic space group T 5 h (Im3), no.…”