SQUID picovoltometry of single crystal Bi2Sr2CaCu2O8+ delta : Observation of the crossover from high-temperature Arrhenius to low-temperature vortex-glass behavior.

Abstract

Using a SQUID voltmeter we have measured current-voltage curves in untwinned crystals of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ as a function of temperature and magnetic field. Our data show a clear crossover from high-temperature Arrhenius behavior to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents \ensuremath{\nu}(z-1)=7\ifmmode\pm\else\textpm\fi{}1 in this system are in accord with theoretical models and previous measurements in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. The width of the critical region collapses below 2 T, reflecting the changing role of dimensionality with field.