High quality superconducting Josephson junctions on LiNO3 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 DIgR2 mV swhere DIg is the current jump at the sum gap voltage and R2 mV the static resistance at V=2 mVd 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.