Vortex lattice structure in Bi2Sr2CaCu2O8+delta at high temperatures

The microscopic structure of the magnetic Bur-line lattice (FLL) in Bi2Sr7CaCu2O8+delta superconductors was studied at temperatures up to 77 K by decoration. Comparison of FLLs obtained at 55 and 4.2 K shows that twisted bond defects are a manifestation of thermal fluctuations at elevated temperature. Analyses of the orientational and translational correlation functions for field and zero-field cooled lattices obtained at 55 K suggest that the observed FLL is an equilibrium hexatic. These data were also used to estimate the FLL freezing temperature.