Fluxoid quantization effects in superconducting mesoscopic Al multiloop structures

We have studied fluxoid quantization effects in mesoscopic Al samples consisting of a small number of square loops. In short microladders a pronounced substructure of the Little-Parks oscillations (i.e. the oscillations of the critical temperature Tc as a function of the applied magnetic flux ${\mit \Phi}$) has been found. These new features in $T_{\rm c}({\mit \Phi})$ originate from transitions between different quantum states, each having a specific order parameter profile and flow pattern of the supercurrents. The experimental data are in excellent agreement with the $T_{\rm c}({\mit \Phi})$ calculated within the de Gennes-Alexander model for superconducting micronetworks