Discovery of superconductivity in β-Nb₂N and its electronic properties

Since the discovery of relatively high Tc in δ-NbN in 1941, the Nb-N system has been studied extensively. However, during the last 80 years, superconductivity of β-Nb₂N has not been observed due to its relatively low Tc and the difficulty in making a high quality crystal of this phase. We present the growth conditions used to make phase-pure β-Nb₂N using Molecular Beam Epitaxy (MBE), its electronic and structural properties and its superconducting transition at about 0.5K. β-Nb₂N, due to its hexagonal symmetry, is symmetry-matched to Wurtzite AlN and coincidentally they are also lattice matched. This allows us to grow highest quality Josephson Junctions (JJs) where the barrier and the superconductor belong to same family of materials (Nitrides in our case) and are symmetry and lattice matched. Devices were fabricated out of β-Nb₂N/AlN/β-Nb₂N JJ heterostructure and their properties will be discussed.