Current transfer lengths and the origin of linear components in the voltage-current curves of Ag-sheathed BSCCO components

The commonly observed linear sections in the voltage-current characteristics of Ag-sheathed BSCCO-2212 and BSCCO-2223 composites were studied. One source of such characteristics is due to ohmic losses in the silver at the current feed points. Characteristic current transfer lengths are of the order of millimetres at 4.2 K and tenths of millimetres at 77 K, However, linear components can also be observed well away from current feed points. These were found to be associated with regions of locally reduced critical current, which provoke local transfer of the excess current into the Ag, thus producing local, ohmic V-I characteristics. Because of the finite current transfer length, some ohmic voltage can be detected even outside regions of reduced critical current. When the silver was removed from lower critical current regions, ohmic voltages were no longer observed, even when the critical current was severely reduced by local damage with a laser, Within the range of electric field covered by this experiment (0.05-100 mu V cm(-1)), we conclude that all ohmic voltages are produced by current flow in Ag.