Experimental evidence of the decoupling line in Bi 2212 single crystal by electronic transport measurements

Both in-plane rho (ab) and out-of-plane rho (c) resistivities measurements have been measured on Bi 2212 single crystals with a magnetic field applied along the c-axis direction. By studying the temperature dependence of the resistivity ratio, rho (ab)/rho (c), we identify a pancake "vortex gas" pha se. This phase is limited at low temperature by a crossover to an anisotrop ic tridimensional vortex lines liquid phase in which we observe a thermally activated behavior of rho (ab) which is in good agreement with the vortex loop creation model. Our data suggest a dimensional crossover describing th e decoupling of the liquid state into a decoupled pancake "vortex gas" stat e well above the first order melting line.