CURRENT DISTRIBUTION AND SUPERCONDUCTIVIT Y DESTRUCTION IN LARGE CONTACTS CONTAINING TYPE-II SUPERCONDUCTOR

The phenomena related to the electron transport in normal metal - type II superconductor contacts (1-70 mum in diameter) are studied. Superc onductivity is destroyed on achieving the critical current density ind ucing a continuous motion of vortices. The voltage at the critical poi nt V(c1) is not directly connected with the superconductor energy gap as is was assumed earlier but is dictated by the normal electrode and depends on the relation between the electron mean free path in the nor mal metal l(i) and the contact diameter d. Different current distribut ion can occur in point contacts. For relatively clean normal metal con tacts (l(i) approximately d) and clean contacts with a thin defective layer at the boundary between the electrodes, the current density is c onstant over the contact cross-section. In ultimately dirty contacts ( l(i) much-less-than d) an annular current flow takes place, whose dens ity is low at the center and increases towards the contact periphery. In S-c-S contacts in zero external magnetic fields the current also fl ows along a ring whose width starts to increase when the current-excit ed field exceeds H(c1) and the vortices penetrate into the contact cro ss-section.