### ?

## Extraordinary kinetic inductance of superconductor/ferromagnet/normal metal thin strip in an Fulde–Ferrell state

We have calculated kinetic inductance *L*k of a thin superconductor/ferromagnet/normal metal strip in an in-plane Fulde–Ferrell (FF) state. We consider range of parameters when FF state appears at temperature *T*FF < *T*c (*T*c is a transition temperature to superconducting state) when the paramagnetic response of FN layers overcomes the diamagnetic response of S layer. We show that *L*k diverges at *T* = *T*FF which is consequence of the second order phase transition to FF state, similar to divergency of *L*k at *T* = *T*c. Kinetic inductance also diverges at finite magnetic field at *T* < *T*FF which is consequence of magnetic field driven second order transition to/from FF state. Due to presence in the FF state finite supervelocity, at low current there are two states (metastable and ground) which have different *L*k. Metastable state is unstable above some critical current which is much smaller than depairing current, above which the ground state becomes unstable. It results in strong dependence of *L*k on current not only at large currents (near depairing current) but at low currents too. We argue that found properties could be useful in various applications which exploit temperature, current and magnetic field dependence of the kinetic inductance.