Pair charging gap observed near the magneticc-field-induced superconductor-insulator transition in granular films

Abstract

Measured differential resistance (DR) of granular In/InOx films near the magnetic-field-induced superconductor-insulator (SI) transition is reported. In the field-induced transition regime a sharp zero-bias peak in the DR developed inside the superconducting (SC) gap of the grains, where time gap itself was much weakened in the field. We confirmed that the peak in the DR originated from the Coulomb blockade of pair tunnelings between adjacent grains. It strongly suggests that, in granular systems, the global SI transition is caused by fluctuations between grains as the pair tunnelings are reduced due to grain charging effect.