Flux-periodicity crossover from h/2e to h/e in aluminium nano-loops

We study the magnetoresistance of aluminium 'double-networks' formed by connecting the vertexes of nano-loops with relatively long wires, creating two interlaced subnetworks of small and large loops (SL and LL, respectively). Far below the critical temperature, Aharonov-Bohm like quantum interference effects are observed for both the LL and the SL subnetworks. When approaching T _c, both exhibit the usual Little-Parks oscillations, with periodicity of the superconducting flux quantum Φ ₀ =h/2e. For one sample, with a relatively large coherence length, ξ, at temperatures very close to T _c, the Φ ₀ periodicity of the SL disappears, and the waveform of the first period is consistent with that predicted recently for loops with a size a < ξ, indicating a crossover to 2Φ ₀ periodicity.