Indications of pair electron effect above field induced superconductor–insulator transition in amorphous ultra thin W films with Si/W/Si structure

Abstract

We present the measurements of the superconductor–insulator transition (SIT) driven by both thickness and magnetic field for the Si/a–W/Si system. The thickness of the W-film was varied over a range from 1 to 5 nm. We found the universal quantum sheet resistance at SIT driven by thickness. Field induced SIT for two samples with 1.6 and 3 nm W thick was investigated in detail. In the insulator side, the evidence of Bose glass state for our homogeneous disordered two dimensional system is inferred by comparing SIT field B c with the upper critical field at 0 K H c2(0) estimated from measurements of d H c2/d T| T c and the field dependent magneto-resistance at various temperatures.