Quantum crossover in moderately damped epitaxial NbN/MgO/NbN junctions with low critical current density

摘要

High quality epitaxial NbN/MgO/NbN Josephson junctions have been realizedwith MgO barriers up to a thickness of d=1 nm. The junction propertiescoherently scale with the size of barrier, and low critical current densitiesdown to 3 A/cm$^2$ have been achieved for larger barriers. In this limit,junctions exhibit macroscopic quantum phenomena for temperatures lower than 90mK. Measurements and junction parameters support the notion of a possible useof these devices for multiphoton quantum experiments, taking advantage of thefast non equilibrium electron-phonon relaxation times of NbN.