Above-gap Conductance Anomaly Studied in Superconductor-graphene-superconductor Josephson Junctions

TL;DR

This study explores the electrical transport in superconductor-graphene-superconductor Josephson junctions, revealing an above-gap conductance anomaly linked to electron heating, with implications for understanding superconducting proximity effects.

Contribution

It uncovers an above-gap conductance anomaly in SGS junctions and links it to electron temperature effects, providing new insights into high-bias transport phenomena.

Findings

Observed an anomalous conductance jump above the superconducting gap

Identified the anomaly's dependence on electron temperature and bias power

Demonstrated the anomaly's insensitivity to backgate voltage at a characteristic power

Abstract

We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. In low voltage bias, we observed conventional proximity-coupled Josephson effect, such as the supercurrent flow through the graphene, sub-gap structure of differential conductance due to Andreev reflection, and periodic modulation of the critical current Ic with perpendicular magnetic field H to the graphene. In high bias above the superconducting gap voltage, however, we also observed an anomalous jump of the differential conductance, the voltage position of which is sensitive to the backgate voltage Vg. Our extensive study with varying Vg, temperature, and H reveals that the above-gap structure takes place at a characteristic power P*, which is irrespective of Vg for a given junction. Temperature and H dependences of P* are well explained by the increase of the electron temperature in graphene.