EVIDENCE FOR 2-DIMENSIONAL THERMAL FLUCTUATIONS OF THE VORTEX STRUCTURE IN BI2.15SR1.85CACU2O8+DELTA FROM MUON SPIN ROTATION EXPERIMENTS

In the mixed state of Bi2.15Sr1.85CaCu2O8+delta the temperature depend ence of the muon spin rotation (mu SR) linewidth is found to have a st rong field dependence, which is attributed to the effect on the line s hapes resulting from thermal fluctuations of the vortex positions. Thi s provides important information concerning the form of the fluctuatio ns and moreover gives a measure of the anisotropy parameter gamma. By combining this result with a mu SR determination of the penetration de pth lambda(T) and the melting line B-m(T), we are further able to obta in the Lindemann number c(L).