Measurements on Superconducting Nanorings Smaller than the Coherence Length*

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, \emph{PRL} \textbf{9}, 9 (1964){]}. 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. \emph{PRB} \textbf{78}, 174526 (2008){]} and references therein. The destructive regime has also been observed experimentally in cylinders whose diameter is small compared to the coherence length {[}Y. Liu, et al. \emph{Science} \textbf{294}, 2332 (2001){]}. We present experimental work in an effort to achieve this limit in Al nanorings prepared by electron beam lithography. These measurements achieve a regime hitherto unexplored in nanorings with interesting consequences.