  We have performed high-resolution angle-resolved photoemission spectroscopy
of ternary pnictide CaAuAs which is predicted to be a three-dimensional
topological Dirac semimetal (TDS). By accurately determining the bulk-band
structure, we have revealed the coexistence of three-dimensional and
quasi-two-dimensional Fermi surfaces with dominant hole carriers. The band
structure around the Brillouin-zone center is characterized by an energy
overlap between hole and electron pockets, in excellent agreement with
first-principles band-structure calculations. This indicates the occurrence of
bulk-band inversion, supporting the TDS state in CaAuAs. Because of the high
tunability in the chemical composition besides the TDS nature, CaAuAs provides
a precious opportunity for investigating the quantum phase transition from TDS
to other exotic topological phases.
