Evidence of Vortices on the Insulating Side of the Superconductor-Insulator Transition

TL;DR

This study investigates magnetoresistance in ultrathin Bi films near the superconductor-insulator transition, providing evidence that vortices exist on the insulating side, challenging traditional quantum interference explanations.

Contribution

It presents experimental evidence of vortices on the insulating side of the superconductor-insulator transition, a novel insight into the transition's nature.

Findings

Magnetoresistance is negative deep in the localized regime.

Magnetoresistance becomes positive with increasing film thickness.

Vortices are suggested to exist on the insulating side of the transition.

Abstract

The magnetoresistance of ultrathin insulating films of Bi has been studied with magnetic fields applied parallel and perpendicular to the plane of the sample. Deep in the strongly localized regime, the magnetoresistance is negative and independent of field orientation. As film thicknesses increase, the magnetoresistance becomes positive, and a difference between values measured in perpendicular and parallel fields appears, which is a linear function of the magnetic field and is positive. This is not consistent with the quantum interference picture. We suggest that it is due to vortices present on the insulating side of the superconductor-insulator transition.