Fluxoid Quantization in Superconducting Al Nano-Rings

The Little-Parks experiment on superconducting cylinders is an important demonstration of fluxoid quantization in superconductors. The transition temperature oscillations in magnetic field have a period of $h/2e$ for the micro cylinders in their studies, which was further evidence for Cooper paring at the time {[}W. A. Little, R. D. Parks, PRL 1964, 9, 9{]}. However recent theoretical works have suggested that in superconducting loops smaller than the coherence length this period changes from $h/2e$ to $h/e$, for details see {[}F. Loder, et al. PRB, 2008, 78, 174526{]} and references therein. We present experimental work in an effort to achieve this limit with Al nano-rings prepared by electron beam lithography. The rings presented here are smaller than others reported in the literature by as much as a factor of two or three {[}H. Wang, et al. PRB, 2007, 75, 064509{]}.