Superconductivity of alpha-gallium probed on the atomic scale by normal and Josephson tunneling

TL;DR

This study uses advanced tunneling techniques to analyze the superconducting properties of alpha-gallium at the atomic scale, confirming BCS theory applicability and exploring Josephson effects, thus advancing surface science of mesoscopic superconductivity.

Contribution

First detailed atomic-scale investigation of alpha-gallium's superconductivity using STM and spectroscopy, including Josephson junction analysis with Coulomb blockade modeling.

Findings

Superconducting gap Δ_Ga = 163 μeV on the (112) facet.

Superconducting spectra are highly homogeneous across the surface.

Josephson junction features are well described by Coulomb blockade theory.

Abstract

We investigate superconducting gallium in its $\alpha$ phase using scanning tunneling microscopy and spectroscopy at temperatures down to about 100 mK. High-resolution tunneling spectroscopies using both superconducting and normal tips show that superconducting $\alpha$-Ga is accurately described by Bardeen-Cooper-Schrieffer theory, with a gap $\Delta_{\rm Ga}$ = 163 $\mu$eV on the $\alpha-$Ga(112) facet, with highly homogeneous spectra over the surface, including atomic defects and step edges. Using a superconducting Pb tip, we furthermore study the low-bias conductance features of the Josephson junction formed between tip and sample. The features are accurately described by dynamical Coulomb blockade theory, highlighting $\alpha-$Ga as a possible platform for surface science studies of mesoscopic superconductivity.