Negative magneto- and electroresistance of silicon films with superconducting nanopreciptates - the role of inelastic cotunneling

The electronic transport properties of insulating Si:Ga films with superconducting, Ga-rich nanopreciptates are investigated in dependence on temperature, current, and magnetic field. The large negative magnetoresistance, observed below the critical temperature, can be explained by Cooper pair breaking and subsequent tunneling of the fermionic quasiparticles. Localization due to quantum interferences of bosons or fermions, as recently discussed, seems not to be the reason for the insulating state and the large magnetoresistance. Cooper pair tunneling is blocked by the high Coulomb barrier. The quasiparticles can overcome the barrier by inelastic cotunneling that results in nonlinear current-voltage characteristics and negative electroresistance. Since the experimental results obtained for the Si:Ga film resemble that of many other films with superconducting nanoprecipitates the conclusions drawn here could be quite general.