Anomalous Thermoelectric Response in an Orbital-Ordered Oxide Near and Far from Equilibrium

TL;DR

This study investigates the thermoelectric behavior of Ca$_2$RuO$_4$ near and far from equilibrium, revealing non-thermal effects that alter the Seebeck coefficient through orbital and spin state modifications.

Contribution

It uncovers non-thermal, non-equilibrium effects on thermoelectric response in an orbital-ordered oxide, highlighting the impact of high electrical currents on orbital and spin states.

Findings

Seebeck coefficient shows non-monotonic temperature dependence near equilibrium.

High electrical currents increase the magnitude of the Seebeck coefficient.

Non-thermal effects modify orbital and spin states under current application.

Abstract

We report the thermoelectric transport properties in the orbital-ordered Mott insulating phase of Ca$_2$RuO$_4$ close to and far from equilibrium. Near equilibrium conditions where the temperature gradient is only applied to the sample, an insulating but non-monotonic temperature variation of the Seebeck coefficient is observed, which is accounted for in terms of a temperature-induced suppression of the orbital order. In non-equilibrium conditions where we have applied high electrical currents, we find that the Seebeck coefficient is anomalously increased in magnitude with increasing external current. The present result clearly demonstrates a non-thermal effect since the heating simply causes a decrease of the Seebeck coefficient, implying a non-trivial non-equilibrium effect such as a modification of the spin and orbital state in currents.