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. The authors demonstrate here 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 tunneling 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.

Top: on the left, the junctions’ sketch. On the right, transmission electron microscope image of the interface between the junction materials. Bottom: on the left, switching of the tunnel conductance by application of voltage pulses of amplitude Vpol. The switching takes place between two conductance levels separated by several orders of magnitude. It is bipolar and reversible. On the right: electronic density of states in the electrode (green=high density), in a temperature-energy diagram.

This work is the result of a collaboration between the CNRS/Thales Joint Lab (Palaiseau), the LPEM (ESPCI, Paris), the LOMA (University of Bordeaux) and the Complutense University of Madrid (Spain), and was funded by the ERC “SUSPINTRONICS” and the ANR “SUPERTRONICS”.

Contact: Javier E. Villegas

V. Rouco, R. El Hage, A. Sander, J. Grandal, K. Seurre, X. Palermo, J. Briatico, S. Collin, J. Trastoy, K. Bouzehouane, A. I. Buzdin, G. Singh, N. Bergeal, C. Feuillet-Palma, J. Lesueur, C. Leon, M. Varela, J. Santamaría & Javier E. Villegas, Nature Communications 11, 658 (2020)