High-quality superconducting Josephson junctions on LiNbO3 electro-optical crystals

The attainment of high-quality Josephson junctions on electro-optical substrates constitutes a key step toward the fabrication of functional superconducting opto-electronics. We report on the fabrication of high-quality all-refractory niobium superconducting tunnel junctions deposited on X-cut LiNbO3 single crystals. A high quality factor Vm = 0.7 ?IgR2 mV (where ?Ig is the current jump at the sum gap voltage and R2 mV the static resistance at V = 2 mV) up to 61 mV has been measured at T = 4.2 K. The very low contribution of subgap leakage currents is demonstrated by the BCS-like quasiparticle current measured at V = 0.1 mV down to T = 1.9 K.