Temperature controlled FFLO instability in superconductor-ferromagnet hybrids

TL;DR

This paper demonstrates that layered superconductor-ferromagnet hybrids can exhibit a temperature-controlled transition to the FFLO phase, with potential for observable effects at several kelvins, especially with added normal metal layers.

Contribution

It reveals the conditions under which the FFLO phase emerges in S/F hybrids and how normal metal layers facilitate this transition at accessible temperatures.

Findings

FFLO phase appears below the superconducting transition temperature.

Adding a normal metal layer lowers the transition temperature into the FFLO state.

Transition involves damping of the Meissner response and sign change in current-velocity curvature.

Abstract

We show that a wide class of layered superconductor-ferromagnet (S/F) hybrids demonstrate the emergence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase well below the superconducting transition temperature. Decreasing the temperature one can switch the system from uniform to the FFLO state which is accompanied by the damping of the diamagnetic Meissner response down to zero and also by the sign change in the curvature of the current-velocity dependence. Our estimates show that an additional layer of the normal metal (N) covering the ferromagnet substantially soften the conditions required for the predicted FFLO instability and for existing S/F/N systems the temperature of the transition into the FFLO phase can reach several kelvins.