  The recent discovery of Weyl fermions in solids enables exploitation of
relativistic physics and development of a spectrum of intriguing physical
phenomena. They are constituted of pairs of Weyl points with two-fold band
degeneracy, which in principle can be hosted in any materials without inversion
or time-reversal symmetry. However, previous studies of Weyl fermions have been
limited exclusively to semimetals. Here, by combining magneto-transport
measurements, angle-resolved photoemission spectroscopy, and band structure
calculations, Weyl fermions are identified in an elemental semiconductor
tellurium. This is mainly achieved by direct observation of the representative
transport signatures of the chiral anomaly, including the negative longitudinal
magnetoresistance and the planar Hall effect. Semiconductor materials are well
suited for band engineering, and therefore provide an ideal platform for
manipulating the fundamental Weyl fermionic behaviors. Furthermore,
introduction of Weyl physics into semiconductors to develop "Weyl
semiconductors" also creates a new degree of freedom for the future design of
semiconductor electronic and optoelectronic devices.
