Modulated vortex states in Rashba non-centrosymmetric superconductors

TL;DR

This paper investigates vortex lattice structures in Rashba non-centrosymmetric superconductors under magnetic fields, revealing a transition from FFLO-type modulated states to new gap amplitude modulated states influenced by spin-orbit coupling.

Contribution

It introduces a theoretical analysis of vortex lattice modulations considering spin-orbit coupling and paramagnetic effects, highlighting a transition between different vortex states in non-centrosymmetric superconductors.

Findings

FFLO-type vortex lattice appears at low spin-orbit coupling.

A new vortex lattice with gap amplitude modulation emerges at higher spin-orbit coupling.

Structural transition correlates with the upper critical field curve.

Abstract

Vortex lattice structures to occur in Rashba non-centrosymmetric superconductors under a magnetic field parallel to the basal plane are studied by assuming a singlet Cooper pairing and taking account of both the paramagnetic and orbital depairings. A vortex lattice of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type with modulation perpendicular to the field is expected to occur in the limit of vanishing ${\tilde \eta}$, where ${\tilde \eta}$ is the spin-orbit coupling {\it normalized} by Fermi energy. As ${\tilde \eta}$ increases, however, this state tends to be replaced by another new vortex lattice with a modulation of the gap amplitude parallel to the helical phase modulation induced by the absence of inversion symmetry. Differences of the present results from those in the Pauli limit and a correlation of a structural transition with the $H_{c2}(T)$-curve are discussed in relation to possible experimental realization.