POSITRON-ANNIHILATION STUDIES ON A TETRAGONAL CALABACU3O6.85 SUPERCONDUCTOR

We report on a new result on positron annihilation studies in a single phase tetragonal CaLaBaCu3O6.85 (CLBCO) superconductor (a clone of YB CO) using Doppler broadened annihilation radiation (DEAR) measurements and positron life-time spectroscopy. A clear discontinuity in the S-p arameter is seen at the onset of superconductivity. Also, the life-tim e is seen to decrease in the superconducting state. The result is comp ared with that of YBCO and the temperature dependence is explained inv oking a local charge-transfer mechanism at the onset of T-c.