Vortex dynamics in a Bi2Sr2CaCu2O8 crystal with columnar defects

The frequency-dependent shielding of an applied ac field is used to study the vortex dynamics in a Bi2Sr2CaCu2O8 single crystal irradiated with 5.8-GeV Pb ions. At fields below the matching field BΦ200 G, the sample exhibits strong pinning due to the irradiation-induced columnar defects. The dynamics in this field regime is shown to be in accurate agreement with the predictions of the Bose-glass theory of Nelson and Vinokur [Phys. Rev. B 48, 13 082 (1993)]. We propose to explain deviations from the Bose-glass predictions at fields greater than BΦ, and temperatures exceeding 85 K, by vortex decoupling and the appearance of a surface barrier, respectively. The crossover between creep of pancake vortices above BΦ and Bose-glass creep below BΦ is marked by a break in the irreversibility line. At all temperatures the irreversibility field is determined by the disappearance of the shielding current due to flux creep. No evidence for critical scaling of the resistivity was found.