Induced Kramer-Pesch-Effect in a Two Gap Superconductor: Application to MgB2

TL;DR

This paper investigates the Kramer-Pesch effect in two-gap superconductors, specifically MgB2, showing that the effect can be induced in the dirty band even if only one band is clean, supported by numerical and analytical models.

Contribution

It demonstrates the existence of an induced Kramer-Pesch effect in two-gap superconductors with mixed clean and dirty bands, extending understanding beyond single-gap cases.

Findings

The Kramer-Pesch effect exists in both bands of MgB2 even if only one is in the clean limit.

An analytical model for the vortex core radius near the vortex center is developed.

Numerical results support the presence of an induced Kramer-Pesch effect in the dirty band.

Abstract

The size of the vortex core in a clean superconductor is strongly temperature dependent and shrinks with decreasing temperature, decreasing to zero for T -> 0. We study this so-called Kramer-Pesch effect both for a single gap superconductor and for the case of a two gap superconductor using parameters appropriate for Magnesium Diboride. Usually, the Kramer-Pesch effect is absent in the dirty limit. Here, we show that the Kramer-Pesch effect exists in both bands of a two gap superconductor even if only one of the two bands is in the clean limit and the other band in the dirty limit, a case appropriate for MgB2. In this case an induced Kramer-Pesch effect appears in the dirty band. Besides numerical results we also present an analytical model for the spatial variation of the pairing potential in the vicinity of the vortex center that allows a simple calculation of the vortex core radius even in the limit T -> 0.