Critical behavior of vortices in epitaxial Tl‐2201 films at zero external field

The resistive transition and current–voltage characteristics of a Tl‐2201 superconducting microbridge are measured close to the critical temperature in zero external magnetic field. The dissipation mechanism is studied by analyzing d V /d I and power dissipation P (= IV ) as functions of transport current. The J c – T curves exhibit three distinct types of behavior depending on temperature. In the low temperature regime, the critical current density is proportional to (1 – T / T c ). At intermediate temperatures, thermally activated flux creep dominates and J c is proportional to 1 – n ( T / T c ) – m ( T / T c ) 2 . In the high temperature regime, J c is equal to the G – L depairing current. The depinning current, J c 1 , is determined, taking into account thermally activated flux motion and flux motion induced by the transport current. J c 1 depends linearly on temperature and vanishes at 82 K, J c 1 = J c 1 (0) (1 – T / T c 1 ). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)