Large spectral gap and impurity-induced states in a two-dimensional Abrikosov vortex

TL;DR

This paper investigates the subgap spectrum of a 2D Abrikosov vortex in an s-wave superconductor, revealing multiple spectral branches and impurity-induced states, with implications for experimental observation via scanning tunneling spectroscopy.

Contribution

It provides a detailed analysis of the vortex subgap spectrum, including the effects of impurities and magnetic screening, using both Eilenberger and Gor'kov formalisms, which is novel in the context of 2D vortices.

Findings

Multiple subgap spectral branches can exist in 2D vortices.

A single impurity can induce up to four discrete quasiparticle states.

Most spectral features are observable in scanning tunneling spectroscopy.

Abstract

We study the subgap spectrum of a 2D Abrikosov vortex in an s-wave superconductor in the absence and presence of a point impurity. By solving the Eilenberger equations without impurity for two models of the vortex (including a self-consistent one), we find multiple subgap spectral branches. The number of these branches may be arbitrary large provided that the magnetic field screening length is large enough. The quasiclassical spectrum of the vortex has a local gap with a width of the order of the bulk gap and a spatial extent of several coherence lengths. The existence of such gap is the prerequisite for the appearance of discrete impurity-induced states. Within the Gor'kov equations formalism, we find that a single impurity induces up to four discrete quasiparticle states in the vortex. The energies and wavefunctions of the impurity states are calculated for different parameters. We claim that most of the predicted spectral features can be observed in scanning tunnel spectroscopy experiments.