Experimental Evidence for a First-Order Magnetic Transition in Thin Superconducting Aluminum Films

Abstract

We have measured the critical magnetic field $H_c$ of aluminum films, 50-220 Å thick, at temperatures between 0.4°K and the transition temperature. For the thinnest films a qualitative change in the form of the transition for $\frac{T}{T_c}<0.5\mathrm{}$ indicates the presence of the first-order phase transition predicted for paramagnetically limited superconductors. The results also seem to demonstrate the existence of fluctuation broadening at higher temperatures.