Effects of gap anisotropy upon the electronic structure around a superconducting vortex

TL;DR

This paper investigates how anisotropy in the superconducting energy gap influences the electronic structure around a vortex in a superconductor, using quasiclassical theory to explain STM observations in 2H-NbSe2.

Contribution

It demonstrates that gap anisotropy is essential for understanding vortex bound states and reproduces experimental STM features with an anisotropic s-wave gap model.

Findings

Reproduces STM-observed vortex LDOS structure in 2H-NbSe2

Highlights importance of gap anisotropy for bound states

Predicts additional fine structures in LDOS for future observation

Abstract

An isolated single vortex is considered within the framework of the quasiclassical theory. The local density of states around a vortex is calculated in a clean type II superconductor with an anisotropy. The anisotropy of a superconducting energy gap is crucial for bound states around a vortex. A characteristic structure of the local density of states, observed in the layered hexagonal superconductor 2H-NbSe2 by scanning tunneling microscopy (STM), is well reproduced if one assumes an anisotropic s-wave gap in the hexagonal plane. The local density of states (or the bound states) around the vortex is interpreted in terms of quasiparticle trajectories to facilitate an understanding of the rich electronic structure observed in STM experiments. It is pointed out that further fine structures and extra peaks in the local density of states should be observed by STM.