Magnetic-flux periodic response of nanoperforated ultrathin superconducting films

We have patterned ultrathin $\mathrm{Bi}∕\mathrm{Sb}$ films with a hexagonal array of nanoscale holes. These regular perforations result in a phase-sensitive periodic response to an applied magnetic field. Thus by measuring this response in the resistive transitions we are able to distinguish between superconducting fluctuations of the amplitude and phase. Our results delineate three distinct portions of the $R(T)$ in which fluctuations of the amplitude, both the amplitude and phase, and the phase of the superconducting order parameter dominate. In addition, as ${T}_{c0}$ is lowered the region of the superconducting transition dominated by amplitude fluctuations is large and grows with proximity to the superconductor to insulator transition.