Emergence of a metallic metastable phase induced by electrical current in Ca2RuO4

A comprehensive study of the behavior of the Mott insulator Ca2RuO4 under electrical current drive is performed by combining two experimental probes: The macroscopic electrical transport and the microscopic X-ray diffraction. The resistivity, ρ, versus electric current density, J, and temperature, T,ρ(J,T), resistivity map is drawn. In particular, the metastable state, induced between the insulating and the metallic thermodynamic states by current biasing Ca2RuO4 single crystals, is investigated. Such an analysis, combined with the study of the resulting RuO6 octahedra energy levels, reveals that a metallic crystal phase emerges in the metastable regime. The peculiar properties of such a phase, coexisting with the well-established orthorhombic insulating and tetragonal metallic phases, allow one to explain some of the unconventional and puzzling behaviors observed in the experiments as a negative differential resistivity.