On the origin of the controversial electrostatic field effect in superconductors

I Golokolenov,Yu A Pashkin,A Guthrie,V Tsepelin,S Kafanov

doi:10.1038/s41467-021-22998-0

Abstract

Superconducting quantum devices offer numerous applications, from electrical metrology and magnetic sensing to energy-efficient high-end computing and advanced quantum information processing. The key elements of quantum circuits are (single and double) Josephson junctions controllable either by electric current or magnetic field. The voltage control, commonly used in semiconductor-based devices via the electrostatic field effect, would be far more versatile and practical. Hence, the field effect recently reported in superconducting devices may revolutionise the whole field of superconductor electronics provided it is confirmed. Here we show that the suppression of the critical current attributed to the field effect, can be explained by quasiparticle excitations in the constriction of superconducting devices. Our results demonstrate that a miniscule leakage current between the gate and the constriction of devices perfectly follows the Fowler-Nordheim model of electron field emission from a metal electrode and injects quasiparticles with energies sufficient to weaken or even suppress superconductivity.

Highlights

Superconducting quantum devices offer numerous applications, from electrical metrology and magnetic sensing to energy-efficient high-end computing and advanced quantum information processing
A supercurrent through the whole structure was observed and controlled electrostatically by a nearby gate, due to the proximised superconductivity in the semiconductor[13,14,15]. At low voltages these devices act as Josephson junctions with a gate-controlled critical current, at high voltages they behave as conventional fieldeffect transistor (FET)
A series of four meander-shaped resonators are incorporated into a manifold frequency multiplexing network (FMN)[21], which allows independent probing of each resonator at its resonance frequency using a single feedline

Summary

Introduction

Superconducting quantum devices offer numerous applications, from electrical metrology and magnetic sensing to energy-efficient high-end computing and advanced quantum information processing. The effect was discovered in gated nanoscale constrictions and nanowires as a suppression of the critical current under the application of intense electric field and interpreted in terms of an electric field-induced perturbation propagating inside the superconducting film This interpretation is in stark contrast to the existence of the commonly accepted screening effect in metals. A mesoscopic superconductor–normal metal–superconductor Josephson junction was predicted[9] and realised[10] by controlling the supercurrent flow via a “normal” current traversing the normal metal between the superconducting electrodes[11] This control was attributed to the modified quasiparticle distribution, which was driven far from equilibrium by a voltage applied across the normal metal. At low voltages these devices act as Josephson junctions with a gate-controlled critical current, at high voltages they behave as conventional FETs

Methods

Results

Conclusion