Europhys. Lett.
Volume 65, Number 4, February 2004
Page(s) 540 - 545
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 February 2004
Europhys. Lett., 65 (4) , pp. 540-545 (2004)
DOI: 10.1209/epl/i2003-10123-2

Current-dependent crossover in the flux dynamics of $\chem{MgB_2}$ thin films

S. L. Prischepa, M. Salvato and L. Maritato

Dipartimento di Fisica "E. R. Caianiello", Università di Salerno and INFM/Coherentia - Via S. Allende, I-84081 Baronissi (SA), Italy

(Received 19 June 2003; accepted in final form 10 December 2003)

We have investigated the dissipative behaviour of $\chem{MgB_2}$ textured thin films at different perpendicular magnetic fields H and bias currents J, to study activation energy dependencies U(J) and U(H). For J<J*, where J* is a magnetic-field-dependent crossover current, activation energies are weakly current dependent, $U(J)\approx$ const, while, for J>J*, $U(J)\sim-\ln J$. At J<J*, the magnetic-energy dependencies are logarithmic, $U(H)\sim-\ln H$, while for J>J*, $U(H)\sim H^{-1}$, up to $\mu_0H\approx 5$ $\un{T}$. The J*(H) curve separates two zones with different vortex dynamics. We discuss the J*(H) curve in terms of a current-driven transition from a thermally activated flux flow to a flux creep regime. For pronounced disorder, the data suggest the influence of the activation energy distribution on the U(J) and U(H) dependencies.

74.78.-w - Superconducting films and low-dimensional structures.

© EDP Sciences 2004