Influence of columnar defects on surface resistance of YBa2Cu3Ox superconducting thin films; nonlinear effects

We report on measurements of surface resistance (R-s) of YBa2Cu3Ox thin fil ms irradiated with 0.9 GeV Pb ions. Measurements of R-s versus microwave-fr equency (rf) magnetic field and temperature were carried out using a dielec tric resonator technique. At low temperatures, no significant difference wa s observed between surface resistance of irradiated and nonirradiated films . However, at higher temperatures the irradiated films exhibited not only h igher R-s but also a nonlinear dependence of R-s on rf magnetic field. A si mple model for microwave losses in thin superconducting films induced by co lumnar defects is proposed. Using this model, the observed changes in R-s h ave been attributed to additional losses and/or heating effects in the insu lator-superconductor boundary between an amorphous core of the columnar def ects (several nanometers in diameter) and the surrounding superconducting m aterial. (C) 1999 American Institute of Physics. [S0003-6951(99)04638-0].