AC response of vortices subjected to pinning by columnar defects in Tl<SUB>2</SUB>Ba<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8</SUB> epitaxial films

A micro-Hall-probe-based ac susceptometer is used to study the dynamics of vortices in Tl2Ba2CaCu2O8 (Tl-2212) epitaxial films with and without correlated disorder in a low field (lt;6 kG) and high temperature (Tgt;60 K) regime. The Bean critical state model for a thin superconducting disc in perpendicular magnetic field is used to extract the critical current density of the films. The temperature and frequency dependence of the irreversibility field (Birr) is compared for samples with and without the linear defects. The Birr(T) curve shows a distinct discontinuity at B&#8776;B&#966;. The frequency dependence of the screening current density J(&#969;), extracted from the inphase component (TH) of the fundamental transmittivity, has been analyzed in the framework of Bose glass dynamics. This analysis shows that the vortex depinning temperature is &#8776;24 K for this Tl-2212 film and the depinning process starts via excitations of half-loops. The angle dependent studies of the susceptibility further suggest that these half-loops consist of many pancake vortices