  Tantalum arsenide is a member of the non-centrosymmetric monopnictides, which
are putative Weyl semimetals. In these materials, three-dimensional chiral
massless quasiparticles, the so-called Weyl fermions, are predicted to induce
novel quantum mechanical phenomena, such as the chiral anomaly and topological
surface states. However, their chirality is only well-defined if the Fermi
level is close enough to the Weyl points that separate Fermi surface pockets of
opposite chirality exist. In this article, we present the bulk Fermi surface
topology of high quality single crystals of TaAs, as determined by
angle-dependent Shubnikov-de Haas and de Haas-van Alphen measurements combined
with ab-initio band-structure calculations. Quantum oscillations originating
from three different types of Fermi surface pocket were found in magnetization,
magnetic torque, and mag- netoresistance measurements performed in magnetic
fields up to 14 T and temperatures down to 1.8 K. Of these Fermi pockets, two
are pairs of topologically non-trivial electron pockets around the Weyl points
and one is a trivial hole pocket. Unlike the other members of the
non-centrosymmetric monopnictides, TaAs is the first Weyl semimetal candidate
with the Fermi energy suffciently close to both types of Weyl points to
generate chiral quasiparticles at the Fermi surface.
