Magnetic-field-driven superconductor insulator transition in granular In/InOx films

Abstract

We have measured the differential resistance of granular In/InOx films near the magnetic-field-driven superconductor-insulator (SI) transition. We observed the development of a sharp zero-bias peak in the differential resistance inside the superconducting gap in the field-driven insulating regime. We confirmed that the peak in the differential resistance originated from the Coulomb blockade of pair tunnelings between adjacent superconducting grains. Although almost full phase fluctuations are induced in a magnetic field which is far lower than the critical field of the SI transition, the global SI transition in granular systems is caused by additional phase fluctuations along with reduced pair tunnelings due to Coulomb blockade between superconducting grains.