Electrical transport properties of C$_{60}$ superconductors in the vicinity of Mott metal-insulator transition

It was revealed in 2008 that Cs$_{3}$C$_{60}$ showed superconductivity up to 38K under high pressure [1]. As the lattice constant is increased, the superconducting critical temperature ($T_{C})$ decreases after experiencing the maximum $T_{C}$ and finally Cs$_{3}$C$_{60}$ becomes a Mott insulator [2]. This result suggests that C$_{60}$ superconductors cannot be simply explained by the BCS theory [1-4]. There are strong electron correlations in the vicinity of Mott metal-insulator transition. Electrical transport properties are required because they provide us importantly intrinsic information on the electronic states, but the systematical electrical transport measurements have not been made due to the experimental difficulties. It will be reported that we have successfully obtained the electrical transport properties of expanded C$_{60}$ superconductors in pellet form by using a specially designed pressure cell. [1] A. Y. Ganin \textit{et al.}, \textit{Nat. Mater}. \textbf{7}, 367 (2008). [2] A. Y. Ganin \textit{et al.}, \textit{Nature} \textbf{466}, 221 (2010). [3] Y. Takabayashi \textit{et al.}, \textit{Science}, \textbf{323}, 1585 (2009). [4] R. H. Zadik \textit{et al.}, \textit{Sci. Adv.} \textbf{1}, e1500059 (2015).