Symmetry-enforced Fermi degeneracy in topological semimetal RhSb3

Predictions of a topological electronic structure in the skutterudite TPn3 family (T=transition metal, Pn = pnictogen) are investigated via magnetoresistance, quantum oscillation, and angle-resolved photoemission experiments on RhSb3, a semimetal with low carrier density. Electronic band structure calculations and symmetry analysis of RhSb3 indicate this material to be a zero-gap semimetal protected by symmetry with inverted valence and conduction bands that touch at the Gamma point close to the Fermi level. Transport experiments reveal an unsaturated linear magnetoresistance that approaches a factor of 200 at 60 T magnetic fields and quantum oscillations observable up to 150 K that are consistent with a large Fermi velocity (similar to 1.3 x 10(6) m/s), high carrier mobility [-14 m(2)/(V s)], and the existence of a small three-dimensional hole pocket. A very small, sample-dependent effective mass falls to values as low as 0.018(2) of the bare electron mass and scales with the Fermi wave vector. This, together with a nonzero Berry's phase and the location of the Fermi level in the linear region of the valence band, suggests RhSb3 as representative of a material family of topological semimetals with symmetry-enforced Fermi degeneracy at the high-symmetry points.