Abstract
We deposited amorphous Bi films with a thickness between 3 and 6.5 nm at 4.2 K on top of previously deposited Co clusters having a mean size of ∼4.5 nm. The Co cluster layers thickness was between 2.3 and 5 nm. In-situ electrical transport measurements were performed between 2 and 100 K. Measurements on as-prepared samples having a Bi layer thickness of 3.0 nm show hopping (tunneling) conductivity as σ(T) = σ 0 exp[−(T 0/T)1/2] above the superconducting transition temperature T C and re-entrance behavior again with hopping (tunneling) conductivity below T C . Annealing of films having a Bi layer thickness of 5.5 nm results in a decrease of resistivity, with variable-range hopping conduction behavior as σ(T) = σ 0 exp[−(T 0/T)1/3 ]. Quite different are the findings for films having a Bi layer thickness of 6.5 nm: annealing of these films results in a power-law behavior as σ(T) = σ 0 T α with α = 2/3, indicating that these films are close to a quantum critical point separating superconducting and insulating phases. A phase diagram including all experimental observations is proposed.
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Herrera, W.T., Dinola, I.S., Continentino, M.A. et al. Superconductor-insulator transition tuned by annealing in Bi-film on top of Co-clusters. Eur. Phys. J. B 86, 508 (2013). https://doi.org/10.1140/epjb/e2013-40337-3
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DOI: https://doi.org/10.1140/epjb/e2013-40337-3