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Theoretical Analysis of Drag Resistance in Amorphous Thin Films Exhibiting Superconductor-Insulator-Transition

The magnetical field tuned superconductor-insulator transition in amorphous thin films, e.g., Ta and InO, exhibits a range of yet unexplained curious phenomena, such as a putative low-resistance metallic phase intervening the superconducting and the insulating phase, and a huge peak in the magnetoresistance at large magnetic field. Qualitatively, the phenomena can be explained equally well within several significantly different pictures, particularly the condensation of quantum vortex liquid, and the percolation of superconducting islands embedded in normal region. Recently, we proposed and analyzed a new measurement that should be able to decisively point to the correct picture: a drag resistance measurement in an amorphous thin-film bilayer setup. Neglecting interlayer tunneling, we found that the drag resistance within the vortex paradigm has opposite sign and is orders of magnitude larger than that in competing paradigms. For example, two identical films as in Sambandamurthy et al. 2004 with 25 nm layer separation at 0.07 K would produce a drag resistance $\sim10^{-4}Ω$ according the vortex theory, but only $\sim10^{-12}Ω$ for the percolation theory. We provide details of our theoretical analysis of the drag resistance within both paradigms, and report some new results as well.