A class of high-Tc YBa2Cu3O7−x grain boundary junctions with high-IcRn products

The properties of symmetric 24° and asymmetric 45° [100] tilt YBa2Cu3O7−x bicrystal grain boundary junctions (GBJs) have been extensively investigated. A large number of junctions, with dimensions ranging from 2 to 20 µm, have been fabricated and characterized at 4.2 K. Experimental data have been compared with [001] tilt bicrystal and [100] tilt biepitaxial YBa2Cu3O7−x junctions. [100] GBJs show high IcRn products in the range 5–10 mV at T = 4.2 K, these being slightly sensitive to the critical current density values. A direct tunnelling mechanism for both Cooper pair and quasiparticles has been evidenced. The reduced IcRn values of asymmetric 45° with respect to symmetric 24° [100] tilt GBJs have been accounted for by considering a d-wave symmetry of the order parameter using the Sigrist–Rice equation.