POSSIBLE NEW VORTEX MATTER PHASES IN BI2SR2CACU2O8

The vortex matter phase diagram of Bi2Sr2CaCu2O8 crystals is analyzed by investigating vortex penetration through the surface barrier in the presence of a transport current. The strength of the effective surfac e barrier and its nonlinearity and asymmetry are used to identify a po ssible new ordered phase above the first-order transition. This techni que also allows sensitive determination of the depinning temperature. The solid phase below the first-order transition is apparently subdivi ded into two phases by a vertical line extending from the multicritica l point.