Evidence for High T$_{c}$ Superconducting Transitions in Isolated Al$_{45}^{-}$ and Al$_{47}^{-}$ Nanoclusters

Heat capacities measured for Al$_{45}^{-}$ and Al$_{47}^{-}$ nanoclusters have reproducible peaks at $\sim $ 200 K. The data were obtained using a multi-collision dissociation method [1] allowing us to perform measurements for isolated nanoclusters. The peaks are observed for selected Al clusters only. These peaks are consistent with theoretical predictions that some clusters with highly degenerate electronic states near the Fermi level will undergo a transition into a high T$_{c}$ superconducting state [2]. An analysis based on a theoretical treatment of pairing in Al$_{45}^{-}$ and Al$_{47}^{-}$ agrees well with the experimental data in both the value of the critical temperature and in the size and width of the peaks in the heat capacity. The observed value of T$_{c}$ exceeds those found in bulk systems. [1] G.Breaux, C.Neal, B.Cao, M.Jarrold, Phys. Rev. Lett. \textbf{94}, 173401 (2005) [2] V.Z.Kresin, Yu.Ovchinnikov, Phys. Rev. B \textbf{74}, 024514 (2006)