EVIDENCE FOR A VORTEX-GLASS TRANSITION FOR B-PERPENDICULAR-TO-C IN BI2SR2CACU2O8

Between 0.1 Hz and 50 MHz the conductivity sigma(omega) is determined from the ac-susceptibility measured in a field of 1T parallel and perp endicular to ($) over right arrow c. For ($) over right arrow B parall el to ($) over right arrow c, thermally activated dynamics is observed down to T-m approximate to 20 K where melting of a 2D vortex-lattice is expected. Below T-m, the dynamics is algebraic, sigma(omega) simila r to (i omega)(-0.5) with no signs of a vertex-glass (VG) down to 10 K . For ($) over right arrow B perpendicular to ($) over right arrow c, dynamical scaling of sigma(omega) reveals a VG transition at T-g = 26 K which may be related to the binding of dislocation pairs in the ab-p lanes.