Nonlinear thermoelectric effects in MoGe films

Thermoelectric effects refer to the voltage generation from temperature gradients in a solid. Although the linear thermoelectric effects have been used in heat-power generation, the thermoelectric voltage disappears when temperature fluctuates temporarily or spatially without macroscopic temperature gradients, limiting their application. In contrast to the linear thermoelectric effects, nonlinear thermoelectric effects, which have been theoretically predicted, can convert temperature fluctuations into electric power, breaking through the limit. In this talk, we report second-order nonlinear thermoelectric effects in a superconducting MoGe film on a ferrimagnetic insulator Y₃Fe₅O₁₂. We found that the MoGe film exhibits a voltage proportional to the square of the applied temperature gradient. In the MoGe film, mobile superconducting vortices, which generate a thermoelectric voltage, can sense the different magnetic environment between the top and bottom surfaces. Our theoretical analysis shows that the magnetic asymmetry between the surfaces of the MoGe film is attributable to the nonlinear thermoelectric effects. Our result will offer an operating principle for power generators from temperature fluctuations.