Absence of a Zero Temperature Vortex Solid Phase in Strongly Disordered Superconducting Bi Films

TL;DR

This study investigates ultrathin amorphous Bi films near the resistance quantum, revealing the absence of a vortex solid phase at high disorder levels and discussing implications for superconductor-insulator transitions.

Contribution

It demonstrates that strong disorder suppresses the vortex solid phase in superconducting Bi films, challenging previous assumptions about vortex states at high resistance.

Findings

Vortex solid signatures appear only when resistance is below the quantum resistance.

Above the quantum resistance, resistive tails are non-activated, indicating no vortex solid.

Disorder-induced fluctuations can eliminate the vortex solid phase.

Abstract

We present low temperature measurements of the resistance in magnetic field of superconducting ultrathin amorphous Bi films with normal state sheet resistances, $R_N$, near the resistance quantum, $R_Q={\hbar\over {e^2}}$. For $R_N<R_Q$, the tails of the resistive transitions show the thermally activated flux flow signature characteristic of defect motion in a vortex solid with a finite correlation length. When $R_N$ exceeds $R_Q$, the tails become non-activated. We conclude that in films where $R_N>R_Q$ there is no vortex solid and, hence, no zero resistance state in magnetic field. We describe how disorder induced quantum and/or mesoscopic fluctuations can eliminate the vortex solid and also discuss implications for the magnetic-field-tuned superconductor-insulator transition.