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Electrostatic manipulation of High-Tc superconductivity: the hammer and the scalpel
Javier E. Villegas - Unité Mixte de Physique CNRS/Thales, Palaiseau, France
Mercredi 30/01/2019, 11:00-12:00
SPEC Salle Itzykson, Bât.774, Orme des Merisiers


Field-effect devices based on oxide superconductors constitute an interesting playground to investigate a rich variety of physical phenomena. They also bear much potential for novel functionalities. To illustrate that, I will show transport experiments on junctions between oxide-superconductors and non-superconducting materials, in which the conductance is modulated by electric field effects via different mechanisms.
First I will briefly discuss the observation of quasiparticle tunnel electroresistance in superconducting junctions. The term “tunnel electroresistance” was formerly coined to describe a non-volatile resistive switching observed in ferroelectric tunnel junctions upon application of a voltage pulse. This effect, which has opened the door to a new class of memories, can be explained by subtle mechanisms related to the nonvolatile reversal of the ferroelectric polarization. Our experiments with superconducting electrodes demonstrate that the same electroresistance can be produced by a more prosaic mechanism: oxygen electro-migration and the resulting modification of the electrodes’ ground-state. Furthermore, we demonstrate that the electroresistance is orders-of-magnitude stronger for quasiparticles than for normal electrons [1.2].
Second, I will discuss the electrostatic manipulation of the proximity effect in cuprate superconductor/graphene junctions [3]. Here, the underlying mechanism is the controlled variation the graphene’s Fermi vector through electrical gating. This allows tuning electron interferences that modulate the Andreev reflection at the superconductor/graphene interface. Furthermore, a different type of interferences –this time controlled by the bias voltage– are observed which are due to geometrical resonances and the coherent propagation of electron/hole pairs in graphene.
[1] L. Bégon-Lours et al, Physical Review Materials
[2] V. Rouco et al, submitted
[3] D. Perconte et al. Nature Physics 14, 25 (2018)
*In collaboration with: D. Perconte, V. Rouco, C. Ulysse, D. Bercioux, J. Trastoy, A. Sander, P. R. Kidambi, S. Hofmann, B. Dlubak, P. Seneor, F. S. Bergeret, R. El Hage, J. Grandal, J. Briatico, S. Collin, K. Bouzehouane, A.I. Buzdin, G. Singh, N. Bergeal, C. Feuillet-Palma, J. Lesueur, M. Varela, and J. Santamaría
Work supported by the ERC grant Nº 647100, French ANR grant ANR-15-CE24-0008-01 and COST “Nanoscale Coherent Hybrid Devices For Superconducting Quantum Technologies” - Action CA16218.

A coffee break will be served at 11h00.



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