Evidence for three-dimensional flux creep in thin-film Bi2Sr2CaCu2O8+δ

We have measured sweep-rate-dependent magnetization hysteresis curves of thin-film Bi2Sr2CaCu2O8+δ using a Hall probe magnetometer in an unconventional geometry. We find a structure in the response well below the three-dimensional to two-dimensional crossover field. The observed strong enhancement of the perpendicular field component's creep rate in the presence of an in-plane applied magnetic field is in contrast to recent findings. We attribute this to the existence of a finite correlation length between vortex pancakes along the field direction larger than the interlayer spacing leading to a three-dimensional behavior of flux lines in Bi2Sr2CaCu2O8+δ at 77 K