Magnetotransport measurements in aluminium nano loop array

Aalto Quantum Physics Seminar (Micronova). Speaker: Ms. Rebekka Garreis (University of Konstanz, Germany).

In 1963, Little and Parks demonstrated experimentally that the charge carriers in superconductors amount twice the single electron charge. For several thin walled hollow cylinders, they measured a periodic dependence of the critical temperature with the periodicity of the flux quantum h/2e, resulting in a change in the resistivity at the critical temperature with the magnetic field. This effect can be described as fluxoid quantisation in superconducting rings. Amongst others, the coherence length of the superconductor determines these oscillations. Theory predicts a crossover to a h/e periodicity in the magneto-resistance if the ring dimensions become smaller than the coherence length. Even though only hints for the predicted crossover were measured experimentally so far, investigations on aluminium double networks consisting of decoupled small rectengular loops and coupled large loops reveal several interesting features.