VORTEX SHEAR MODULUS AND LATTICE MELTING IN TWIN BOUNDARY CHANNELS OFYBA2CU3O7-DELTA

Melting of the vortex lattice is probed directly by investigating the flow of vortices in channels created by twin boundaries. The angular-d ependent resistivity p(T,H)(theta) has a maximum above the melting tem perature T-m and crosses over to a minimum below, corresponding to the onset of a shear modulus which reduces vortex how in the channels. A peak effect in the critical current below T-m is accompanied by a shar p increase in the twin boundary pinning accommodation angle. We calcul ate the effective twin boundary pinning energy by relating the accommo dation angle to a thermal depinning angle.