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Séminaire confinement quantique - matériaux 2D

Putting a spin on the Josephson Effect - Marcelo Goffman - Mardi 18 décembre 2018 à 11 h

INSP - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Marcelo Goffman - Chercheur CEA dans le groupe Quantronics du Service de Physique de l’état Condensée (SPEC) - CNRS /université Paris-Saclay

Abstract

The Josephson supercurrent that flows through a weak link between two superconductors is mediated by quasiparticle states localized at the weak link : the Andreev bound states. Spectroscopy experiments on carbon nanotubes [1], atomic-size contacts [2] and semiconducting nanowires [3] have clearly revealed these fermionic states. The role of spin of these excitations, however, is still not unveiled. This is a topical issue in the rapid growing fields of hybrid superconducting devices [4] and of topological superconductivity [5]. In this talk, I will present the microwave spectroscopy of superconducting weak links with strong spin-orbit coupling realized on an InAs-Al (core-full shell) epitaxially-grown nanowire. The spectra present distinctive features that we interpret as arising from zero-field spin-split Andreev states. A simple analytical model, which takes into account the Rashba spin-orbit interaction in a multichannel nanowire, explains these features and their evolution with magnetic field. Our results show that the spin of quasiparticles can be a relevant degree of freedom in Josephson weak links.

Work done in collaboration with L. Tosi, C. Metzger, C. Urbina and H. Pothier from Quantronics, Sunghun Park and A. Levy Yeyati from Departamento de Fisica Teorica de la material Condensada, Universidad de Madrid, Spain and J. Nygard and P. Krogstrup from Center for Quantum devices and Station Q Copenhagen, Denmark.

[1] J. D. Pillet et al., Nat. Phys. 6, 965 (2010).

[2] L. Bretheau et al., Nature 499, 312 (2013) ; C. Janvier et al., Science 349, 1199 (2015).

[3] E. J. H. Lee et al., Nat. Nanotech. 9, 79 (2014) ; D. J. Woerkom et al., Nat. Phys. 13, 876 (2017).

[4] S. De Franceschi et al., Nat. Nanotech. 5, 703 (2010).

[5] A. Zazunov et al., Phys. Rev. B 96, 024516 (2017) ; M. T. Deng et al., Phys. Rev. B 98, 085125 (2018).