SQUID PICOVOLTOMETRY OF SINGLE-CRYSTAL BI2SR2CACU2O8+DELTA - OBSERVATION OF THE CROSSOVER FROM HIGH-TEMPERATURE ARRHENIUS TO LOW-TEMPERATURE VORTEX-GLASS BEHAVIOR

Using a SQUID voltmeter we have measured current-voltage curves in untwinned crystals of Bi2Sr2CaCu2O8 + delta as a function of temperature and magnetic field. Our data show a clear crossover from high-temperature Arrhenius behavior to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z - 1) = 7 +/- 1 in this system are in accord with theoretical models and previous measurements in YBa2Cu3O7. The width of the critical region collapses below 2 T, reflecting the changing role of dimensionality with field.