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 dependence of the muon spin rotation (mu SR) linewidth is found to have a strong field dependence, which is attributed to the effect on the line shapes resulting from thermal fluctuations of the vortex positions. This provides important information concerning the form of the fluctuations and moreover gives a measure of the anisotropy parameter gamma. By combining this result with a mu SR determination of the penetration depth lambda(T) and the melting line B-m(T), we are further able to obtain the Lindemann number c(L).