PINNING EFFECT ON FLUCTUATION CONDUCTIVITY IN A SUPERCONDUCTING UNTWINNED YBA2CU3O7-DELTA SINGLE-CRYSTAL WITH COLUMNAR DEFECTS

The effect of columnar defects on the critical dynamics of a supercond ucting untwinned YBa2Cu3O7-delta (YBCO) single crystal has been invest igated. The columnar defects are produced by Sn ion irradiation of whi ch dose corresponds to a matching field of 1 T. The in-plane longitudi nal resistivity of the irradiated YBCO crystal has been measured as a function of magnetic field H and temperature T. The extracted fluctuat ion conductivities are enhanced by the strong pinnings and do not exhi bit the same three-dimensional (3D) XY scaling behavior as for the uni rradiated YBCO single crystal; particularly at the magnetic field valu es near the matching field of 1 T, the fluctuation conductivities show a clear deviation from the critical dynamics. At higher magnetic fiel ds, however, the signature of the 3D-XY scaling appears.