Preparation of ramp-edge Josephson junctions with natural barriers

We have demonstrated ramp-edge Josephson junctions using high temperature superconductors without depositing artificial barriers. We use a surface barrier formed naturally during an etching process by an Ar ion beam. The resistivity of the barrier, which is evaluated in the Nb/Au/YBCO structures, changes over 4 orders in accordance with the gas pressure in the vacuum annealing executed before the deposition of the counter-electrode. All the junctions having a YBCO/barrier/YBCO structure exhibit RSJ-like current-voltage characteristics over the entire temperature range of operation. Fraunhofer-like modulation patterns are observed with a very small amount of excess current even at low temperatures except for large junctions. The temperature dependence of J(c) and R(n)A are similar to those in HTS grain boundary junctions. Since the junction parameters are controlled by the total pressure during the vacuum annealing, the junctions made through this procedure have a potential for circuit applications.