Vortex Imaging in the pi-Band of Magnesium Diboride

TL;DR

This study uses scanning tunneling spectroscopy to image vortices in MgB2, revealing unique vortex core properties in the pi-band and suggesting induced superconductivity from the sigma-band.

Contribution

First direct imaging of vortex lattice in MgB2's pi-band, showing large vortex cores and absence of localized states, indicating induced superconductivity.

Findings

Large vortex core size in pi-band

Absence of localized states in vortex cores

Superconductivity in pi-band is induced by sigma-band

Abstract

We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2. By tunneling parallel to the c-axis, a single superconducting gap (Delta = 2.2 meV) associated with the pi-band is observed. The vortices in the pi-band have a large core size compared to estimates based on Hc2, and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. These results suggest that superconductivity in the pi-band is, at least partially, induced by the intrinsically superconducting sigma-band.