Scanning Tunneling Spectroscopy on Single Crystal MgB2

TL;DR

This study uses scanning tunneling spectroscopy on single crystal MgB2 to identify two distinct superconducting gaps associated with different electronic bands, revealing unique vortex properties and field responses.

Contribution

It provides direct spectroscopic evidence of two-gap superconductivity in MgB2 and characterizes vortex behavior and anisotropic gap features.

Findings

Identification of two distinct superconducting gaps (Delta_pi and Delta_sigma).

Observation of large vortex core sizes and absence of localized states.

Superconductivity between vortices is rapidly suppressed by magnetic field.

Abstract

We report on the results of scanning tunneling spectroscopy measurements on single crystals of Mg2. Tunneling was performed both parallel and perpendicular to the crystalline c-axis. In the first case, a single superconducting gap (Delta_pi = 2.2 meV) associated with the pi-band is observed. Tunneling parallel to the ab-plane reveals an additional, larger gap (Delta_sigma ~ 7 meV) originating in the highly two-dimensional sigma-band. Vortex imaging in the pi-band was performed with the field and tunnel current parallel to the c-axis. The vortices 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. A comparison to specific heat measurements is performed.