Sub-Gap Structure in the Conductance of a Three-Terminal Josephson Junction

TL;DR

This paper investigates three-terminal superconductor-normal metal-superconductor Josephson junctions, revealing new sub-gap structures linked to correlated Cooper pair motion, supported by theoretical calculations.

Contribution

It introduces the observation of sub-gap structures in three-terminal Josephson junctions and explains them as quartets of entangled Cooper pairs, supported by theoretical modeling.

Findings

Sub-gap structures appear at specific superconductor chemical potentials.

Correlated Cooper pair motion persists above the Thouless energy.

Theoretical calculations support the quartet formation interpretation.

Abstract

Three-terminal superconductor (S) - normal metal (N) - superconductor (S) Josephson junctions are investigated. In a geometry where a T-shape normal metal is connected to three superconducting reservoirs, new sub-gap structures appear in the differential resistance for specific combinations of the superconductor chemical potentials. Those correspond to a correlated motion of Cooper pairs within the device that persist well above the Thouless energy and is consistent with the prediction of quartets formed by two entangled Cooper pairs. A simplified nonequilibrium Keldysh Green's function calculation is presented that supports this interpretation.