Role of local temperature in the current-driven metal–insulator transition of Ca₂RuO₄

It was recently reported that a continuous electric current is a powerful control parameter to trigger changes in the electronic structure and metal–insulator transitions (MITs) in Ca₂RuO₄. However, the spatial evolution of the MIT and the implications of the unavoidable Joule heating have not been clarified yet, often hindered by the difficulty to assess the local sample temperature. We present infrared thermal imaging measurements performed on single-crystal Ca₂RuO₄ while controlling the MIT by electric current. The change in emissivity at the phase transition allows us to monitor the gradual formation and expansion of metallic phase upon increasing current. Our local temperature measurements indicate that, within our experimental resolution, the MIT always occurs at the same local transition temperatures, irrespectively if driven by temperature or by current. Our results highlight the importance of local heating, phase coexistence, and microscale inhomogeneity when studying strongly correlated materials under the flow of electric current.