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Superconducting proximity effects in high-TC hybrids - Javier E. Villegas

Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris Saclay

In artificial hybrids, competing interactions, interplay and proximity effects at the interface between the different constituents often yield to interesting physics, sometimes to novel effects and, occasionally, to new functionalities.
In superconductor-based hybrids, one of the key interaction mechanisms is the proximity effect, via which superconducting correlations leak into a non-superconducting material, eventually allowing it to sustain supercurrents. This effect is very much affected not only by the pairing symmetry in the superconductor, but also by the electronic structure in the non-superconducting material. For example, the presence in the latter of a finite spin polarization (e.g. as in ferromagnets), Dirac fermions (i.e. as in graphene), or spin-orbit coupling (e.g. as in topological insulators) lead to a variety of “exotic” behaviors as compared to the normal-metals case.
In this talk, I will review two examples on which we have been working these last years.
The one is proximity effects at high-temperature superconductor / half-metal ferromagnet oxides, in which the unexpected long-range penetration of superconductivity correlation is explained in terms of equal-spin triplet correlations. I will discuss the controversies, opportunities and challenges brought by this so called spin-polarized superconductivity.
The second example addresses proximity effects at high-temperature superconductors/graphene interfaces. I will discuss the pains and joys of playing with that materials combination, and show conductance experiments in which the Andreev reflection can be modulated electrostatically, which we can understand based on interference effects at the normal-superconductor interface.


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