  The Mott insulator Ca$_2$RuO$_4$ exhibits a rare insulator-to-metal
transition (IMT) induced by DC current. While structural changes associated
with this transition have been tracked by neutron diffraction, Raman
scattering, and x-ray spectroscopy, work on elucidating the response of the
electronic degrees of freedom is still in progress. Here we unveil the
current-induced modifications of the electronic states of Ca$_2$RuO$_4$ by
employing angle-resolved photoemission spectroscopy (ARPES) in conjunction with
four-probe transport. Two main effects emerge: a clear reduction of the Mott
gap and a modification in the dispersion of the Ru-bands. The changes in
dispersion occur exclusively along the $XM$ high-symmetry direction, parallel
to the $b$-axis where the greatest in-plane lattice change occurs. These
experimental observations are reflected in dynamical mean-field theory (DMFT)
calculations simulated exclusively from the current-induced lattice constants,
indicating a current driven structural transition as the primary mechanism of
the IMT. Furthermore, we demonstrate this phase is distinct from the
high-temperature zero-current metallic phase. Our results provide insight into
the elusive nature of the current-induced IMT of Ca$_2$RuO$_4$ and advance the
challenging, yet powerful, technique of transport-ARPES.

Strongly Correlated Electrons