Role of sample geometry on nonlinear transport properties of the vortex solid in Bi2Sr2CaCu2O8

Transport and magnetization measurements have been made on prism- and plate-shaped crystals of Bi2Sr2CaCu2O8. For fields below about 60 Oe the resistivity for the prism and plate specimens is approximately the same above the melting transition temperature, However below this temperature, for equivalent current densities, the (nonlinear) resistivity for the plate goes rapidly to zero, while for the prism it shows a pronounced tail. This behavior is discussed in relation to geometrical effects in the two specimens. It establishes that the nonlinear transport properties of plate-shaped crystals in this regime do not reflect bulk vortex pinning properties and strongly suggests hat the vortex lattice melting is accompanied by vortex decoupling. [S0163-1829(98)04925-X].