Quasiclassical analysis of vortex lattice states in Rashba noncentrosymmetric superconductors

TL;DR

This paper analyzes vortex lattice states in Rashba noncentrosymmetric superconductors using quasiclassical theory, revealing complex phase diagrams with structural transitions and critical points influenced by spin-orbit coupling.

Contribution

It introduces a combined quasiclassical and Landau level approach to study vortex structures, uncovering novel phase transitions and the role of Rashba spin-orbit coupling.

Findings

Identification of discontinuous and continuous vortex lattice transitions.

Discovery of a critical end point in the phase diagram.

Predictions for local density of states observable in STM experiments.

Abstract

Vortex lattice states occurring in noncentrosymmetric superconductors with the spin-orbit coupling of Rashba type under a magnetic field parallel to the symmetry plane are examined by assuming the $s$-wave pairing case and in an approach combining the quasiclassical theory with the Landau level expansion of the superconducting order parameter. The resulting field-temperature phase diagrams include not only a discontinuous transition but a continuous crossover between different vortex lattice structures, and, further, a critical end point of a structural transition line is found in an intermediate field and at a low temperature in the present approach. It is pointed out that the strange field dependence of the vortex lattice structure is a consequence of that of an anisotropy stemming from the Rashba spin-orbit coupling, and that the critical end point is related to the helical phase modulation peculiar to these materials in the ideal Pauli-limited case. Further, calculation results on the local density of states detectable in STM experiments are also presented.