Spin-flip Enhanced Thermoelectricity in Superconductor-Ferromagnet Bilayers

TL;DR

This paper investigates how spin-flip scattering influences thermoelectric effects in superconductor-ferromagnet bilayers, revealing that spin-flip scattering can significantly enhance thermopower due to complex charge and spin interactions.

Contribution

It demonstrates that spin-flip scattering, contrary to expectations, can boost thermoelectric performance in superconductor-ferromagnet heterostructures, supported by theoretical analysis of density of states and thermopower.

Findings

Thermopower exceeds $k_{B}/e$ by about 5 times.

Spin-flip scattering enhances thermoelectricity at low fields and temperatures.

Thermopower shows nonmonotonic dependence on spin-splitting and spin-flip rate.

Abstract

We study the effects of spin-splitting and spin-flip scattering in a superconductor (S) on the thermoelectric properties of a tunneling contact to a metallic ferromagnet (F) using the Green's function method. A giant thermopower has been theoretically predicted and experimentally observed in such structures. This is attributed to the spin-dependent particle-hole asymmetry in the tunneling density of states in the S/F heterostructure. Here, we evaluate the S density of states and thermopower for a range of temperatures, Zeeman-splitting, and spin-flip scattering. In contrast to the naive expectation based on the negative effect of spin-flip scattering on Cooper pairing, we find that the spin-flip scattering strongly enhances the thermoelectric performance of the system in the low-field and low-temperature regime. This is attributed to a complex interplay between the charge and spin conductances caused by the softening of the spin-dependent superconducting gaps. The maximal value of the thermopower exceeds $k_{B}/e$ by a factor of $\approx$ 5 and has a nonmonotonic dependence on spin-splitting and spin-flip rate.