Phase transitions in superconductor/ferromagnet bilayer driven by spontaneous supercurrents

TL;DR

This paper explores how Rashba spin-orbit interaction at the superconductor/ferromagnet interface induces spontaneous supercurrents, affecting the superconducting phase transition, critical temperature, and current anisotropy, with potential experimental implications.

Contribution

It demonstrates the impact of spin-orbit coupling-induced supercurrents on phase transitions and critical temperature shifts in superconductor/ferromagnet bilayers, including first-order transitions and anisotropic effects.

Findings

Spontaneous supercurrents increase the critical temperature in thin superconducting films.

The phase transition can be of the first order in type-I superconducting films.

Critical temperature depends on the orientation of external magnetic and exchange fields.

Abstract

We investigate superconducting phase transition in superconductor(S)/ferromagnet(F) bilayer with Rasba spin-orbit interaction at S/F interface. This spin-orbit coupling produces spontaneous supercurrents flowing inside the atomic-thickness region near the interface, which are compensated by the screening Meissner currents [S. Mironov and A. Buzdin, Phys. Rev. Lett \textbf{118}, 077001 (2017)]. In the case of thin superconducting film the emergence of the spontaneous surface currents causes the increase of the superconducting critical temperature and we calculate the actual value of the critical temperature shift. We also show that in the case of type-I superconducting film this phase transition can be of the first order. In the external magnetic field the critical temperature depends on the relative orientation of the external magnetic field and the exchange field in the ferromagnet. Also we predict the in-plane anisotropy of the critical current which may open an alternative way for the experimental observation of the spontaneous supercurrents generated by the SOC.