ELECTROMAGNETIC PROPERTIES AT THE GRAIN-BOUNDARY INTERFACE OF A YBA2CU3O7-DELTA BICRYSTAL JOSEPHSON-JUNCTION

Electromagnetic resonances along a YBa2Cu3O7-delta bicrystal grain boundary junction made it possible to determine the ratio between the barrier/boundary thickness and the relative dielectric constant t(d)/epsilon(r), the London penetration depth lambda(L), and to estimate the surface resistance R(s) at the interfaces of the grains. From resonances at 256-638 GHz, their Q values, and the Stewart-McCumber parameter, we find t(d)/epsilon(r) approximate to 0.4 nm, lambda(L) = 140+/-30 nm, and R(s) similar to 20 m Omega at f = 280 GHz. This indicates that the boundary is dielectric, and that the grains are well superconducting within 5-20 nm from the boundary interfaces.