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Magnetic, electric-field and light induced control of spin-polarized supercurrents: fundamentals for an offbeat electronics

Periodic Reporting for period 3 - SUSPINTRONICS (Magnetic, electric-field and light induced control of spin-polarized supercurrents: fundamentals for an offbeat electronics)

Reporting period: 2018-10-01 to 2020-03-31

Superconductors are materials in which electrical currents flow without energy loss. Ferroics have a different remarkable property: memory. Among them we find ferromagnets, which present a spontaneous magnetic moment that can be reversed by magnetic field pulses; and ferroelectrics, which present instead a dipolar moment switchable by electric field pulses. All of those properties are of great technological relevance, and hold potential for novel applications. However, those based on superconductors are generally disconnected from those based on ferroics. This is because superconductivity and ferroic order are usually antagonistic –very rare natural materials show both caracteristics simultaneously.

This project is devoted to the study of hybrids in which superconducting and ferroics are deliberately put in intimate contact. This provides a platform to study, understand and control the competing interactions between them. With two main goals. One is to search the conditions under which the coexistence of superconductivity and magnetism can be promoted; for instance, to create and manipulate dissipation-less currents that carry a net spin, or to couple changes in the magnetic moment with changes in the superconducting state. All of that is somewhat equivalent to endowing superconductivity with magnetic memory. The second goal is to transfer into superconductors the ferroic’s sensitivity to certain stimuli (for instance, electric-fields or light).

To reach those goals, the research project encompasses a series of electrical transport experiments in oxide-based superconducting/ferroic heterostructures, junctions and circuits. The work includes the growth, structural and functional characterization of novel materials combinations, as well as the development of approaches for the fabrication nan-junctions and nano-circuits based on them.

The goals we pursue are important for society because they will enlarge fundamental knowledge, and also from the technological point of view, since the expected advances will open the door to new applications in the field of superconducting electronics and spintronics.
After optimizing the growth of different types of oxide heretroctrutures comining superconductors and ferroelectrics, on one side, and superconductors, ferromagnets, half metals and normal metals on the other, we have undertaken different work lines which have allowed

a) exploiting ferroelectric-field effects to modulate Josephson coupling at the nanoscale in planar circuits
b) determining the intrinsic and extrinsic factors that determine the strength of the coupling between ferroelectric polarization and superconducting state
c) demonstrating how ferroelectrics can modify quasiparticle tunneling across vertical junctions.
d) improving the detection of triplet correlations in vertical junctions of half-metals and cuprate superconductors
e) developing a novel nano-lithography approach to design planar circuits of oxide superconductors and half-metals.
f) unveiling two mechanisms of coupling between the superconducting state and magnetization dynamics.
e) creating an experimental set up the coupling manipulating of the interface competing mechanism by visible light.
Among the results that are not confidential at this time (some of key results cannot go public by now):
a) We have realized a rewritable superconducting weak-link produced by ferroelectric field-effect, which demonstrates the concept of reconfigurable superconducting circuits.
b) Our studies on ferroelectric/superconducting heterostructures have unveiled the link the atomic terminations at the interface, the microscale ferroelectric structure, and the size ferroelectric effects on superconductivity. This understanding is crucial and provides the recipe for increasing those effects.
c) Realized a proof-of-concept for a no type of ferroelectric Josephson junction (a patent has been submitted and already published).
d) Unveiled a novel manifestation of the coupling between the ferromagnetic domain structure and the superconducting state in hybrids of both materials.
e) Unveiled a light induced modulation of the electronic phase transition of certain strongly correlated oxides.
Planar reconfigurable Josephson weak-link defined by ferroelectric field effect