Fulde-Ferrell state induced purely by the orbital effect in a superconducting nanowire

TL;DR

This paper shows that a Fulde-Ferrell superconducting phase can be induced solely by the orbital effect in a cylindrical nanowire, leading to unique magnetic field-dependent stability regions.

Contribution

It demonstrates a novel mechanism for FF phase formation driven purely by orbital effects in nanowires, distinct from traditional spin-based mechanisms.

Findings

Orbital effects lift degeneracy and create Fermi wave vector mismatch.

Nonzero Cooper pair momentum compensates for the mismatch, forming FF phase.

Multiple FF stability regions appear with increasing magnetic field.

Abstract

We demonstrate that the Fulde-Ferrell (FF) phase can be induced uniquely by the orbital effect in a cylindrical metallic nanowire. In the external magnetic field the two-fold degeneracy with respect to the orbital quantum number $m$ is lifted what leads to a Fermi wave vector mismatch between the subbands with opposite orbital momenta in the paired state. This mismatch can be compensated by the nonzero total momentum of the Cooper pairs created by electrons from split subbands what results in the formation of the FF phase. With increasing magnetic field a series of FF stability regions appear in between which the standard BCS superconducting phase is stable.