  Strongly correlated iridate pyrochlores with geometrically frustrated spins
have been recognized as a potentially interesting group of oxide materials
where novel topological phases may appear. A particularly attractive system is
the metallic Pr$_2$Ir$_2$O$_7$, as it is known as a Fermi node semimetal
characterized by quadratic band touching at the Brillouin zone center,
suggesting that the topology of its electronic states can be tuned by moderate
lattice strain. In this work we report the growth of epitaxial
Pr$_2$Ir$_2$O$_7$ thin films grown by solid-state epitaxy. We show that the
strained parts of the films give rise to a spontaneous Hall effect that
persists up to 50 K without having spontaneous magnetization within our
experimental accuracy. This indicates that a macroscopic time reversal symmetry
(TRS) breaking appears at a temperature scale that is too high for the
magnetism to be due to Pr 4$f$ moments, and must thus be related to magnetic
order of the iridium 5$d$ electrons. The magnetotransport and Hall analysis
results are consistent with the formation of a Weyl semimetal state that is
induced by a combination of TRS breaking and cubic symmetry breaking due to
lattice strain.
