Title: Dirac dispersion and non-trivial Berry's phase in three-dimensional semimetal RhSb3,
Abstract: We report observations of magnetoresistance, quantum oscillations and
angle-resolved photoemission in RhSb$_3$, a unfilled skutterudite semimetal
with low carrier density. The calculated electronic band structure of RhSb$_3$
entails a $Z_2$ quantum number $\nu_0=0,\nu_1=\nu_2=\nu_3=1$ 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 ($\sim 1.3\times 10^6$ ms$^{-1}$), high
carrier mobility ($\sim 14$ $m^2$/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
RhSb$_3$ is a new class of zero-gap three-dimensional Dirac semimetal.