Vortex shear modulus and lattice melting in twin boundary channels of YBa2Cu3O7-delta

Melting of the vortex lattice is probed directly by investigating the flow of vortices in channels created by twin boundaries. The angular-dependent resistivity p(T,H)(theta) has a maximum above the melting temperature 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 sharp increase in the twin boundary pinning accommodation angle. We calculate the effective twin boundary pinning energy by relating the accommodation angle to a thermal depinning angle.