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