Superconductivity in hole-doped germanium point contacts

TL;DR

This study reports the discovery of superconductivity in heavily p-doped germanium point contacts, characterized by a high superconducting gap and specific magnetic field and temperature dependencies.

Contribution

First observation of superconductivity in heavy p-doped germanium via point contact spectroscopy, with detailed analysis of the superconducting gap and magnetic field effects.

Findings

Superconductivity observed below 6 K and 1 T in p-doped Ge point contacts.

Superconducting gap ratio 2 Delta/kBTc ≈ 10, higher than conventional superconductors.

Magnetic field suppresses Andreev reflection features and moderately decreases the SC gap.

Abstract

We have observed superconductivity in heavy p-doped Ge by measuring of differential resistance dV/dI(V) of Ge - PtIr point contacts. The superconducting (SC) features disappear above 6 K or above 1 T, what can be taken as the critical temperature and the critical magnetic field, respectively. The observed dV/dI(V) spectrum with Andreev reflection like features was fitted within one-gap Blonder-Tinkham-Klapwijk model. The extracted SC gap demonstrates Bardeen-Cooper-Schrieffer-like behavior with 2 Delta/kBTc = 10+/-1 ratio, which is much higher that expected for conventional superconductors. Magnetic field suppresses Andreev reflection features, but the SC gap moderately decreases in magnetic field similarly as it was observed previously for the type-II superconductors, including nickel borocarbide and iron-based superconductors. Curiously, we have not yet observed superconductivity in n-doped Ge with a similar dopant concentration.