FLUXOID QUANTIZATION IN MESOSCOPIC AL MULTILOOP STRUCTURES

Mesoscopic superconducting loops exhibit a well-known h/2e periodic mo dulation of the transition temperature T-c with the enclosed magnetic flux Phi, which is due to the fluxoid quantization. We have found subs tructures of this modulation in the magnetoresistance R(Phi) and the p hase boundaries T-c(Phi) of microladders containing several square loo ps of 1.4 mu m size. The substructures are due to transitions between superconducting states differing in the order parameter profile and th e flow pattern of the supercurrents. The experimental data are in exce llent agreement with the theoretical phase boundaries obtained within the de Gennes-Alexander approach for superconducting micronetworks.