  Dirac and Weyl nodal materials can host low-energy relativistic
quasiparticles. Under strong magnetic fields, the topological properties of
Dirac/Weyl materials can directly manifest through quantum Hall states.
However, most Dirac/Weyl nodes generically exist in semimetals without
exploitable bandgaps due to their accidental band-crossing origin. Here we
report the first experimental observation of Weyl fermions in a semiconductor.
Tellurene, the 2D form of tellurium, possesses chiral crystal structure which
induces unconventional Weyl nodes with a hedgehog-like radial spin texture near
the conduction band edge. We synthesize high-quality n-type tellurene by a
hydrothermal method with subsequent dielectric doping and detect a
topologically non-trivial pi Berry phase in quantum Hall sequences. Our work
expands the spectrum of Weyl matter into semiconductors and offers a new
platform to design novel quantum devices by marrying the advantages of
topological materials to versatile semiconductors.
