We report observations of magnetoresistance, quantum oscillations and
angle-resolved photoemission in RhSb3​, a unfilled skutterudite semimetal
with low carrier density. The calculated electronic band structure of RhSb3​
entails a Z2​ quantum number ν0​=0,ν1​=ν2​=ν3​=1 in analogy to
strong topological insulators, and inverted linear valence/conduction bands
that touch at discrete points close to the Fermi level, in agreement with
angle-resolved photoemission results. 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 (∼1.3×106 ms−1), high
carrier mobility (∼14m2/Vs), and small three dimensional hole pockets
with nontrivial Berry phase. A very small, sample-dependent effective mass that
falls as low as 0.015(7) bare masses scales with Fermi velocity, suggesting
RhSb3​ is a new class of zero-gap three-dimensional Dirac semimetal.Comment: 9 pages, 4 figure