Absence of a zero-temperature vortex solid phase in strongly disordered superconducting Bi films

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, $R_Q=ħ{/e}^2.$ 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 nonactivated. 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.