Comment on ``Quasiparticle Spectra around a Single Vortex in a d-wave Superconductor''

TL;DR

This paper critiques a previous study on quasiparticle states in d-wave superconductors, arguing that their approximation leads to unphysical results and does not accurately describe vortex core states.

Contribution

The authors demonstrate that the approximation used in prior work is inadequate, challenging the validity of the claimed bound states and symmetry properties.

Findings

The approximation used is fundamentally flawed for d-wave vortices.

The observed circular symmetry is an artifact of the approximation.

The actual quasiparticle states differ from those predicted by the flawed model.

Abstract

In a recent Letter Morita, Kohmoto and Maki analyzed the structure of quasiparticle states near a single vortex in a d-wave superconductor using an approximate version of the Bogoliubov - de Gennes theory. Their principal result is the existence of a bound state within the core region at finite energy with full rotational symmetry, which they assert explains the recent scanning tunneling microscopy results on YBCO single crystals. Here we argue that the approximation used in this work is fundamentally inadequate for the description of a d-wave vortex and that the obtained circular symmetry of the local density of states is an unphysical artifact of this approximation.