Transport of Non-Equilibrium Quasiparticle Excitations in Superconducting Aluminum

The electron transport of non-equilibrium quasiparticles injected into superconducting aluminum from a normal metal has been experimentally studied at ultralow temperatures. We studied hybrid nanostructures in the form of a T-shaped normal metal electrode (copper)—a dielectric tunnel layer (aluminum oxide)—a superconducting fork (aluminum), which can be considered as a solid-state analogue of a double-slit optical interferometer. At fixed bias voltages larger than the superconducting gap, a non-monotonic dependence of the tunnel current on perpendicular magnetic field has been observed. The effect is interpreted as the presence of a coherent component of the quasiparticle current.