Magnetic field induced global paramagnetic response in Fulde-Ferrell superconducting strip

TL;DR

This paper theoretically investigates how a superconductor/ferromagnet/normal-metal strip in a Fulde-Ferrell state exhibits a magnetic field-induced transition from diamagnetic to paramagnetic response and back, revealing unique magnetic properties.

Contribution

It introduces the concept that FF superconducting strips can switch magnetic responses with increasing magnetic field, showing a novel paramagnetic phase transition.

Findings

FF strip can switch from diamagnetic to paramagnetic and back with increasing magnetic field

Existence of a magnetic field-driven second order phase transition in FF state

Paramagnetic response linked to nonlinear dependence of supercurrent on supervelocity

Abstract

We theoretically study magnetic response of a superconductor/ferromagnet/normal-metal (SFN) strip in an in-plane Fulde--Ferrell (FF) state. We show that unlike to ordinary superconducting strip the FF strip can be switched from diamagnetic to paramagnetic and then back to diamagnetic state by {\it increasing} the perpendicular magnetic field. Being in paramagnetic state FF strip exhibits magnetic field driven second order phase transition from FF state to the ordinary state without spatial modulation along the strip. We argue that the global paramagnetic response is connected with peculiar dependence of sheet superconducting current density on supervelocity in FF state and it exists in nonlinear regime.