Control of superconducting currents via spin and field effects: fundamentals for an offbeat electronics – SUPERTRONICS

This proposal aims at understanding and tailoring interface interactions between high-temperature superconductors, ferromagnets and ferroelectrics. Despite the fundamental character of the issues investigated, the ultimate goal is to obtain new functionalities based on those interactions. In particular, this project aims at establishing the fundamentals for a new class of superconducting electronics. The basic ingredient for this ambitious project is complex-oxide heterostructures.
The present proposal grounds on earlier results obtained by the project partners, partially within the frame of previous ANR contracts. Those results, and the developed know-how, place this consortium in an especially advantageous position to carry out this research, even when considering an international comparison pool. A key virtue of the consortium is that it combines three teams of experimentalist, one team of nanotechnologists, and one team of theoreticians.
Two main issues are addressed in this project:
1) The one is the possibility to unite the dissipationless, long-range coherent charge transport of superconductors and the spin-polarized one proper of ferromagnets. As recently demonstrated, this is possible via the generation of equal-spin triplet superconducting correlations at the interface between ferromagnets and superconductors. We will first address a series of fundamental questions, in particular about the origin of triplet superconductivity in these systems ?seeking for the ability to switch ON/OFF triplet superconductivity via external stimuli? and on the possibility to transfer it from ferromagnetic to non-magnetic materials. In addition to the fundamental interest it bears, equal-spin triplet superconductivity may open the door to new spintronic applications, in which the information carried by spin-polarized electrons may travel protected by the superconducting correlations, therefore resulting is large “spin signal” Interestingly, these studies will be done with high-temperature superconductors, which endows this research with greater potential for technological applications.
2) The second issue is to the study of Josephson coupling between to superconducting electrode across a ferroelectric spacer, experimentally and theoretically. Almost no previous research has been reported on this issue, and in particular no experimental work exists (due to the difficulty in obtaining sufficiently thin ferroelectric layers, overcome only very recently). Josephson junctions are the cornerstone of classical superconducting electronics, and also a building block for quantum bits. Typically, the Josephson junctions' control parameters are the applied magnetic field and the injected electrical current. The ferroelectric polarization effects sought here would provide an additional external knob to tune Josephson coupling: the momentary application of an electric field or of visible light. Thus, in addition to its fundamental interest, this research may bring novel possibilities to superconducting electronics.