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Polarity dependent heating at the phase interface in metal-insulator transitions

Current-driven insulator-metal transitions are in many cases driven by Joule heating proportional to the square of the applied current. Recent nano-imaging experiments in Ca$_2$RuO$_4$ reveal a metal-insulator phase boundary that depends on the direction of an applied current, suggesting an important non-heating effect. Motivated by these results, we study the effects of an electric current in a system containing interfaces between metallic and insulating phases. Derivation of a heat balance equation from general macroscopic Onsager transport theory, reveals a heating term proportional to the product of the current across the interface and the discontinuity in the Seebeck coefficient, so that heat can either be generated or removed at an interface, depending on the direction of the current relative to the change in material properties. For parameters appropriate to Ca$_2$RuO$_4$, this heating can be comparable to or larger than Joule heating. A simplified model of the relevant experimental geometry is shown to provide results consistent with the experiments. Extension of the results to other inhomogeneous metal-insulator transition systems is discussed.