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 t he resistivity for the prism and plate specimens is approximately the same above the melting transition temperature, However below this temp erature, for equivalent current densities, the (nonlinear) resistivity for the plate goes rapidly to zero, while for the prism it shows a pr onounced tail. This behavior is discussed in relation to geometrical e ffects in the two specimens. It establishes that the nonlinear transpo rt properties of plate-shaped crystals in this regime do not reflect b ulk vortex pinning properties and strongly suggests hat the vortex lat tice melting is accompanied by vortex decoupling. [S0163-1829(98)04925 -X].