Shear viscosity measurements at the vortex melting transition in confined geometry in optimally doped Bi2Sr2CaCu2O8

In order to probe the vortex shear viscosity in the vortex liquid phase, we have introduced two types of vortex-confining structures in optimally doped Bi(2)Sr(2)CaCu(2)O(8) single crystals. First, walls of strong vortex pinning separated by weakly pinning channels are fashioned by heavy ion irradiation through 25 mu m-thick Ni masks. Second, a low density of homogeneously distributed amorphous columnar defects is known to impose as polycrystalline structure to the vortex lattice. Resistivity measurements show that the inclusion of confining structures impede vortex flow in the liquid. The resistivity is remarkably well described by the Halperin-Nelson theory for the viscosity due to free two-dimensional vortex lattice dislocations.