1/f critical current noise in short ballistic graphene Josephson junctions

Francesco M. D. Pellegrino,Giuseppe Falci,Elisabetta Paladino

doi:10.1038/s42005-019-0275-9

Abstract

Short ballistic graphene Josephson junctions sustain superconducting current with a non-sinusoidal current-phase relation up to a critical current threshold. The current-phase relation, arising from proximitized superconductivity, is gate-voltage tunable and exhibits peculiar skewness observed in high quality graphene superconductors heterostructures with clean interfaces. These properties make graphene Josephson junctions promising sensitive quantum probes of microscopic fluctuations underlying transport in two-dimensions. We show that the power spectrum of the critical current fluctuations has a characteristic 1/f dependence on frequency, f, probing two points and higher correlations of carrier density fluctuations of the graphene channel induced by carrier traps in the nearby substrate. Tunability with the Fermi level, close to and far from the charge neutrality point, and temperature dependence of the noise amplitude are clear fingerprints of the underlying material-inherent processes. Our results suggest a roadmap for the analysis of decoherence sources in the implementation of coherent devices by hybrid nanostructures.

Highlights

Short ballistic graphene Josephson junctions sustain superconducting current with a nonsinusoidal current-phase relation up to a critical current threshold
High-quality graphene superconductor heterostructures with clean interfaces, realized by encapsulating graphene in hexagonal boron nitride with one-dimensional edge contacts to superconducting leads, allowed the observation of ballistic transport of Cooper pairs over micronscale lengths, of gate-tunable supercurrents that persist at large parallel magnetic fields[1,2,3] and of different features of 2D Andreev physics[4,5,6]
We show that fluctuations with 1=f power spectrum of the critical current of a short ballistic Graphene Josephson junctions (GJJs) directly probe carrier density fluctuations of the graphene channel induced by the presence of charge traps in the nearby substrate

Summary

Introduction

Short ballistic graphene Josephson junctions sustain superconducting current with a nonsinusoidal current-phase relation up to a critical current threshold. The current-phase relation, arising from proximitized superconductivity, is gate-voltage tunable and exhibits peculiar skewness observed in high quality graphene superconductors heterostructures with clean interfaces. These properties make graphene Josephson junctions promising sensitive quantum probes of microscopic fluctuations underlying transport in two-dimensions. High-quality graphene superconductor heterostructures with clean interfaces, realized by encapsulating graphene in hexagonal boron nitride (hBN) with one-dimensional edge contacts to superconducting leads, allowed the observation of ballistic transport of Cooper pairs over micronscale lengths, of gate-tunable supercurrents that persist at large parallel magnetic fields[1,2,3] and of different features of 2D Andreev physics[4,5,6].

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Results

Conclusion