Vorticity and vortex-core states

TL;DR

This paper investigates the origin of vortex-core states in superconductors, showing that phase topology, not superfluid density suppression, is crucial, and demonstrating their robustness against phase disorder through numerical experiments.

Contribution

It reveals that vortex-core states are primarily due to phase topology rather than superfluid density suppression, challenging potential well interpretations.

Findings

Core states form without superfluid density suppression.

Topological phase defect is crucial for core states.

Core states are robust against phase disorder.

Abstract

The origin of the vortex-core states in s-wave and d_{x^2-y^2}-wave superconductors is investigated by means of some selected numerical experiments. By relaxing the self-consistency condition in the Bogoliubov-de Gennes equations and tuning the order parameter in the core region, it is shown that the suppression of the superfluid density in the core is not a necessary condition for the core states to form. This excludes ``potential well'' types of interpretations for the core states. The topological defect in the phase of the order parameter, however, plays a crucial role. This observation is explained by considering the effect of the vortex supercurrent on the Bogoliubov quasiparticles, and illustrated by comparing conventional vortices with multiply-quantized vortices and vortex-antivortex pairs. The core states are also found to be extremely robust against random phase disorder.