Direct evidence for two-band superconductivity in MgB_2 single crystals from directional point-contact spectroscopy in magnetic fields

TL;DR

This study uses directional point-contact spectroscopy with magnetic fields to directly observe and distinguish the two superconducting gaps in MgB_2 single crystals, providing strong evidence for two-band superconductivity.

Contribution

It introduces a novel directional spectroscopy technique with magnetic fields to separate and measure the two superconducting gaps in MgB_2, enabling more accurate testing of the two-band model.

Findings

Direct measurement of sigma and pi band gaps

Temperature dependence of each gap obtained independently

Supports the two-band superconductivity model in MgB_2

Abstract

We present the results of the first directional point-contact spectroscopy experiments in high-quality MgB_2 single crystals. Due to the directionality of the current injection into the samples, the application of a magnetic field allowed us to separate the contributions of the sigma and pi bands to the total conductance of our point contacts. By using this technique, we were able to obtain the temperature dependency of each gap independent of the other. The consequent, strong reduction of the error on the value of the gap amplitude as function of temperature allows a stricter test of the predictions of the two-band model for MgB_2.