Abnormal magnetoresistance effect in the Nb/Si superconductor-semiconductor heterojunction

Ultrathin superconducting Nb films of about 8 nm thick have been deposited on heavily doped Si substrates through DC magnetron sputtering and then the high-quality Nb/Si superconductor-semiconductor heterojunctions have been fabricated by electron beam lithography and reactive ion etching. An abnormal magnetoresistance effect, which manifests itself as a zero field resistance peak under a magnetic field applied perpendicular to the interface, has been distinctly observed when the Nb film is in the superconductiing state. By considering the heterojunction interface being equivalent to the structure of superconductor-barrier layer-superconductor configuration, we could generally understand this unusual effect based on the Andreev reflection mechanism. Our results can be of help for the future development on compatibility and scalability of the silicon-based nanoscale superconducting devices for integrated circuits and superconducting quantum electronics.