2011/07/14 by Serena Eley, Sarang Gopalakrishnan, Paul M. Goldbart +1 · 2 citations
Physics and Astronomy · #cond-mat.supr-con #cond-mat.mes-hall
paper · pdf · doi:10.1038/nphys2154
published as Nature Physics 8, 59 (2012) · 15 pages, 5 figures
arxiv created 2011/07/14 · arxiv updated 2011/12/30
Systems of superconducting islands placed on normal metal films offer tunable realizations of two-dimensional (2D) superconductivity; they can thus elucidate open questions regarding the nature of 2D superconductors and competing states. In particular, island systems have been predicted to exhibit zero-temperature metallic states. Although evidence exists for such metallic states in some 2D systems, their character is not well understood: the conventional theory of metals cannot explain them, and their properties are difficult to tune. Here, we characterize the superconducting transitions in mesoscopic island-array systems as a function of island thickness and spacing. We observe two transitions in the progression to superconductivity; both transition temperatures exhibit unexpectedly strong depression for widely spaced islands. These depressions are consistent with the system approaching zero-temperature metallic states. The nature of the transitions and the state between them is explained using a phenomenological model involving the stabilization of superconductivity on each island via a weak coupling to and feedback from its neighbors.