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Séminaire NANO

Jeudi 30 avril à 9H30,
Salle Rémy Lemaire, K223

Orateurs : Denis Feinberg et Régis Melin (ThNano)
"DC Josephson currents and quartet resonances in an out-of-equilibrium three-terminal bijunction"

Abstract  :

In this talk we show that a new Josephson physics takes place in a bijunction, e.g. when three (instead of two) superconductors are connected by a small metallic region or a quantum dot. Contrary to a biased simple Josephson junction which only carries AC Josephson currents, a biased bijunction also carries DC Josephson modes, provided the two relevant biases are commensurate. In the simplest case of opposite biases (V, -V), quartet modes made of two entangled pairs flow through the bijunction, despite the fact that each superconductor is a "good" BCS one. This dynamical phenomenon takes place at a resonance formed by multiple Andreev reflections. The quartet current depends on a phase variable that can be in principle controlled with a SQUID-like experiment.

In a disordered metallic bijunction, a recent experiment in F. Lefloch’s group in INAC has indeed shown transport anomalies that can be interpreted in terms of quartet modes. This has motivated new theoretical results for a short metallic bijunction, obtained using quantum circuit theory. Moreover, the coexistence of nonequilibrium dissipative processes and steady coherent channels leads to peculiar properties in terms of slow dynamics, due either to a finite branching time of the couplings, or to the existence of inelastic effects.

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