Strange metal physics at high fields in “clean” CeOs₄Sb₁₂

The filled skutterudite CeOs₄Sb₁₂ has attracted attention because of its proposed topologically protected states and its very striking non-monotonic field (H) - temperature (T) phase boundary that is associated with a valence transition. In its high-H phase at low T, CeOs₄Sb₁₂ possesses a simple, almost spherical Fermi surface. Despite this apparently trivial situation, between fields of 20 T and 50 T, the T- and H-dependent magnetoresistance and Hall effect exhibit unusual behavior that is more characteristic of “strange metals” such as cuprate and pnictide superconductors. However, whereas such conduct is often associated with disorder in the latter systems, CeOs₄Sb₁₂ shows strong magnetic quantum oscillations signifying relative freedom from defects. We speculate that the strange metal physics is here associated with proximity to a quantum-critical point that also results in a H-dependent effective mass.