  A comprehensive study of the behavior of the Mott insulator Ca_2RuO_4 under
electrical current drive is performed by combining two experimental probes: the
macroscopic electrical transport and the microscopic X-Ray diffraction. The
resistivity, rho, vs electric current density, J, and temperature, T ,
rho(J,T), resistivity map is drawn. In particular, the meta-stable state,
induced between the insulating and the metallic thermodynamic states by current
biasing Ca_2RuO_4 single crystals, is investigated. Such an analysis, combined
with the study of the resulting RuO_6 octahedra energy levels, reveals that a
metallic crystal phase emerges in the meta-stable regime. The peculiar
properties of such a phase, coexisting with the well-established orthorhombic
insulating and tetragonal metallic phases, allow to explain some of the
unconventional and puzzling behaviors observed in the experiments, as a
negative differential resistivity.
