  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.
