Talk given by Dr. Régis Mélin Three superconductors contacted within a narrow region form a Josephson bijunction, controlled by two independent voltages, and by two independent phase differences. Coherent DC multipair currents can flow at resonance, for commensurate voltage bias values [1]. The amplitude of those currents depends on the value of a well-defined static phase mode. I will first explain the notion of nonlocal quartets as obtained from the elementary "butterfly" diagram, and explain with an intuitive argument why the quartet current is pi-shifted. Next, I will present the results from the recent Grenoble experiment in the François Lefloch group, in which a T-shaped metallic normal region is connected to three superconductors [2]. This experiment provides evidence for an anomaly in the voltage dependence of the differential resistance, compatible with the quartets in the sense that the signal at resonance shows no sign of weakening even if the bias is increased above about 8 times the Thouless energy. However, this recent experiment does not constitute in itself a direct experimental proof for the quartets. Theoretically, synchronization in this type of bijunction should be reconsidered from the beginning, taking simultaneously quartets and nonequilibrium populations into account. I will then focus on a model of a bijunction formed with two gate-controllable quantum dots [3]. Tuning the dot energies at resonance with the voltages V, -V yields very high values for the phase-sensitive current. In addition, phase-sensitive multiple Andreev reflections appear at higher voltage close to the gap. I will continue with a simpler set-up (a N-Sa-Sb junction) in which a phase-sensitive normal current can appear. This offers the possibility to realize nonconventional side-spectroscopy of a Josephson junction [4]. Finally, I will conclude with our proposal for a new interference device (a bisquid), intended to provide evidence for multipair correlations at equilibrium [5]. References: [1] Production of nonlocal quartets and phase-sensitive entanglement in a superconducting beam splitter, A. Freyn, B. Douçot, D. Feinberg and R. Mélin, Phys. Rev. Lett. 106, 257005 (2011). [2] Transport in a three-terminal Josephson bijunction: sub-gap structure and correlated pair motion, A. Pfeffer, J.-E. Duvauchelle, H. Courtois, R. Mélin, D. Feinberg and F. Lefloch, submitted to Phys. Rev. B (2014). [3] Multipair dc Josephson resonances in a biased all-superconducting bijunction, T. Jonckheere, J. Rech, T. Martin, B. Douçot, D. Feinberg and R. Mélin, Phys. Rev. B 87, 214501 (2013). [4] Phase-sensitive transport at a normal metal-superconductor interface close to a Josephson junction, D. Gosselin, G. Hornecker, R. Mélin and D. Feinberg, Phys. Rev. B 89, 075415 (2014). [5] A proposal for the observation of nonlocal multipair production: the biSQUID, J. Rech, T. Jonckheere, T. Martin, B. Douçot, D. Feinberg, R. Mélin, submitted to Phys. Rev. B (2014).

This event is part of the eventgroup INT Talks

Homepage
https://www.int.kit.edu/events.php

Speaker
Dr. Régis Mélin

Institut Néel, CNRS-UJF, Grenoble, France
Groupe Théorie et Nanosciences

Organizer
Dr. Romain Danneau
Institute of Nanotechnology (INT)
Karlsruhe Institute of Technology (KIT)
Eggenstein-Leopoldshafen
Tel: 0721/608-28896
Mail: romain danneau ∂does-not-exist.kit edu

Targetgroup
Interested / Everyone