  Perovskite SrIrO3 has long been proposed as an exotic semimetal induced by
the interplay between the spin-orbit coupling and electron correlations.
However, its low-lying electronic structure is still lacking. We synthesize
high-quality perovskite SrIrO3 (100) films by means of oxide molecular beam
epitaxy, and then systemically investigate their low energy electronic
structure using in-situ angle-resolved photoemission spectroscopy. We find that
the hole-like bands around R and the electron-like bands around U(T) intersect
the Fermi level simultaneously, providing the direct evidence of the
semimetallic ground state in this compound. Comparing with the density
functional theory, we discover that the bandwidth of states near Fermi level is
extremely small, and there exists a pronounced mixing between the Jeff = 1/2
and Jeff = 3/2 states. Moreover, our data reveal that the predicted Dirac
degeneracy protected by the mirror-symmetry, which was theoretically suggested
to be the key to realize the non-trivial topological properties, is actually
lifted in perovskite SrIrO3 thin films. Our findings pose strong constraints on
the current theoretical models for the 5d iridates.
