PERTURBED-ANGULAR-CORRELATION EXPERIMENTS WITH IN-111 IN MBA2CU3O7-DELTA (M = Y, YB) - THE CU(1)-SITE PUZZLE

Perturbed-angular-correlation spectroscopy has been used to study the hyperfine interaction of In-111 implanted into YbBa2Cu3O7-delta. Five different electric field gradients have been observed that depend on the annealing temperature in a similar way as the ones found with the same probe in YBa2Cu3O7-delta. The comparison with the electric field gradients measured at Cd-111 in the constituents Yb2Cu2O5 and Y2Cu2O5 clearly demonstrates that the hyperfine interactions previously attributed to the Cu(1) site in YBa2Cu3O7-delta have their origin in the Y2Cu2O5 structure. A simple model is proposed that embeds a Y2Cu2O5 or a Yb2Cu2O5 microscopic structure between the (CuO2)infinity planes of the high-T(c) superconductors YBa2Cu3O7-delta or YbBa2Cu3O7-delta, respectively.