Quasiparticle tunnel electroresistance in superconducting junctions

V Rouco,J Trastoy,M Varela,J Grandal,J Briatico,R El Hage,X Palermo,A Sander,C Feuillet-Palma,J Santamaría,K Seurre,A I Buzdin,C Leon,G Singh,K Bouzehouane,Javier E Villegas,S Collin,N Bergeal,J Lesueur

doi:10.1038/s41467-020-14379-w

Abstract

The term tunnel electroresistance (TER) denotes a fast, non-volatile, reversible resistance switching triggered by voltage pulses in ferroelectric tunnel junctions. It is explained by subtle mechanisms connected to the voltage-induced reversal of the ferroelectric polarization. Here we demonstrate that effects functionally indistinguishable from the TER can be produced in a simpler junction scheme—a direct contact between a metal and an oxide—through a different mechanism: a reversible redox reaction that modifies the oxide’s ground-state. This is shown in junctions based on a cuprate superconductor, whose ground-state is sensitive to the oxygen stoichiometry and can be tracked in operando via changes in the conductance spectra. Furthermore, we find that electrochemistry is the governing mechanism even if a ferroelectric is placed between the metal and the oxide. Finally, we extend the concept of electroresistance to the tunnelling of superconducting quasiparticles, for which the switching effects are much stronger than for normal electrons. Besides providing crucial understanding, our results provide a basis for non-volatile Josephson memory devices.

Highlights

The term tunnel electroresistance (TER) denotes a fast, non-volatile, reversible resistance switching triggered by voltage pulses in ferroelectric tunnel junctions
While redox reactions and the resulting changes in the electrodes’ oxidation state may not be the dominant TER mechanism in many of the ferroelectric tunnel junctions studied in the literature, the present study shows that electrochemistry can account for the TER in some cases, in particular if the reduction potential of the involved materials is very different
We show here that functional characteristics of the TER and those that make it unique as compared to other resistive switching phenomena, can be obtained without the use of ferroelectrics if the junction’s electrodes are judiciously chosen

Summary

Introduction

The term tunnel electroresistance (TER) denotes a fast, non-volatile, reversible resistance switching triggered by voltage pulses in ferroelectric tunnel junctions. In most of the existing experiments, at least one of the involved materials (ferroelectric and/or electrodes) is a complex oxide These junctions show a characteristic switching between two (or more) non-volatile resistance states that is obtained by applying few-volts pulses across the ferroelectric barrier. A series of mechanisms explain the TER under the premise that the applied voltage pulses reverse the ferroelectric polarisation[2,15,16]: changes of the orbital hybridisation at the junction interfaces (which modify the probability of electron transmission)[2], piezoelectric effects (which modify the tunnel barrier thickness)[17], and effects related to the screening of the polarisation charges[15]. We found that none of these mechanisms are dominant

Methods

Results

Conclusion