Phase Diagram*

The filled skutterudite compound CeOs₄Sb₁₂ displays Kondo insulating behavior accompanied by a ~1 K Spin-Density-Wave order state. Recently it has also been suggested as a potential topological insulator. In penetration depth and magnetic susceptibility measurements, we found a Fermi-surface reconstruction in CeOs₄Sb₁₂ and an unusual phase boundary in the temperature T vs magnetic field H diagram associated with the valence transition from the Ce⁴⁺ to Ce³⁺ state, denoted as an L and an H phase, respectively. Based on the experimental features from magnetostriction, magnetoresistance, and high T skin depth, a newly modified T-H phase boundary of the L to H phases becoming much broader than what originally thought.^1,2 The cyclotron mass of the conduction electron has a significant enhancement below ~35 T.
¹ arXiv:1907.09181 ² PRB 94, 205140 (2016).