Flux Lattice Melting and Thermal Activation in the High T sub c Superconductor BSCCO

We have studied thermally activated flux flow on single crystal BSCCO using both resistivity and ac susceptibility over the frequency range 10Hz-100MHz for B|| ^ above c and B the perpendicular ^ above c. The same sample was studied with our mechanical oscillator technique used in flux lattice melting studies. Magnetic fields up to 50kG were used. The susceptibility data are approximately fit using a wide range of activation energies centered near 450K. Direct imaging of the flux lattice using the high resolution Bitter technique gives vortex diffusion constants consistent with this picture. The magnetization relaxation time, determined by the mechanical oscillator, gives a dissipation peak displaced from the empirically determined H sub (c2)(w) by a few degrees which can be well fit using a Lindemann melting criterion.