Specific heat of a superconducting multilayer: 2D fluctuations and 2D-0D crossover

Abstract

We have measured the specific heat of multilayers of superconducting amorphous ${\mathrm{Mo}}_{77}$${\mathrm{Ge}}_{23}$ layers separated by insulating amorphous germanium. We observe a fluctuation regime in quantitative agreement with predictions for two-dimensional superconductivity. The fluctuation peak is rapidly suppressed by the application of small magnetic fields perpendicular to the layers, and the transition becomes extremely broad as the field is increased. The transition widths scale as expected for a field-induced 2D to 0D crossover, and are in excellent agreement with the exact result for 0D fluctuations.