Electronic Structure of Vortices Pinned by Columnar Defects

TL;DR

This paper investigates how insulating columnar defects affect the electronic structure of vortex lines in type-II superconductors, revealing the formation of additional spectral branches and the dependence of the minigap on defect size.

Contribution

It provides a detailed analysis of vortex electronic spectra near columnar defects using Bogolubov-de Gennes theory, including spectrum transformation for arbitrary vorticity.

Findings

Additional subgap spectral branch forms due to normal reflection at defect surface.

The minigap increases with the defect radius.

Spectrum transformation scenario is generalized for arbitrary vorticity.

Abstract

The electronic structure of a vortex line trapped by an insulating columnar defect in a type-II superconductor is analysed within the Bogolubov-de Gennes theory. For quasiparticle trajectories with small impact parameters defined with respect to the vortex axis the normal reflection of electrons and holes at the defect surface results in the formation of an additional subgap spectral branch. The increase in the impact parameter at this branch is accompanied by the decrease of the excitation energy. When the impact parameter exceeds the radius of the defect this branch transforms into the Caroli--de Gennes--Matricon one. As a result, the minigap in the quasiparticle spectrum increases with the increase in the defect radius. The scenario of the spectrum transformation is generalized for the case of arbitrary vorticity.