KOSTERLITZ-THOULESS TRANSITION IN HIGH-TC SUPERCONDUCTOR FILMS

Dynamical theory for the polarization of bound vortex-antivortex pairs near the Kosterlitz-Thouless transition (TKT=88.4 K) has been applied to thin films of YBa2Cu3O7. Calculations show that the correct order of magnitude is predicted for the loss function G/c2 at TKT, but the temperature dependence below the transition is wrong. The theoretical value drops much more rapidly with decreasing temperature than observed experimentally. Similar disagreement is found for the penetration depth (T). Estimates of the loss function at microwave frequencies show rather large effects near the critical temperature, but these become negligible by 80 K. The performance of microwave devices operating at liquid-N2 temperature should not be degraded by vortex-antivortex pairs. © 1990 The American Physical Society.