Intrinsically shunted Josephson junctions with high characteristic voltage based on epitaxial NbN/TaN/NbN trilayer

Abstract

We investigate the current–voltage characteristics and the interface properties of epitaxial NbN/TaN/NbN Josephson junctions in this study. The crystal structure and interface properties of the NbN/TaN/NbN junctions are determined using x-ray diffraction and cross-sectional scanning transmission electron microscopy, and the epitaxial growth of the NbN/TaN/NbN trilayer exhibited a smooth and clear interface. The characteristic voltage can be easily tuned over more than one or two orders of magnitude by precisely and independently controlling the barrier thickness and resistivity. For the barrier resistivity of 79 mΩ cm, the junctions show excellent Josephson properties with a characteristic voltage of 2.04 ± 0.08 mV at 4.2 K, corresponding to a large normal metal coherence length of 2.51 ± 0.03 nm and a fast diffusion rate of 24.9 ± 0.4 mm2/s. A high junction quality was also confirmed by the large characteristic voltage of 0.88 ± 0.03 mV at 10.0 K, making the intrinsically shunted NbN junctions promising for use in higher speed and temperature-superconducting devices and circuits.