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Yoshihiko Ihara - LPS, Orsay & Department of Physics, Kyoto university.

Magnetism and pressure induced superconductivity in alkali doped fulleride Cs3C60 studied with 133Cs and 13C NMR

Alkali doped fullerides AxC60 show superconductivity when three electrons are doped into the t1u moleculer orbital of C60 balls. In addition to rather high Tc (up to 40 K), this system is of interest from the viewpoint of strong electron-electron correlations, which is proved from the Mott state in (NH3)xNa3C60 [1] and Mott-Jahn-Teller state [2] in A4C60, A2C60.


The discovery of Cs3C60 with A15 structure opened a way to study the electronic state near Mott transition without any impurity effect caused by NH3 molecules [3]. However, the sample contains three different phases, which are A15 phase Cs3C60, face centered cubic (fcc) phase Cs3C60 and semiconducting Cs4C60.


We succeeded in assigning the NMR signal from each phase in a mixed-phase sample, and investigating their properties separately. The fcc phase is found to be superconducting under pressure, as A15 is, while magnetism at ambient pressure is quite different between the two phases.


[1] M. J. Rosseinsky et al., Nature 364 (1993) 425.
[2] M. Capone et al., PRB 62 (2000) 7619.
[3] A. Y. Ganin et al., Nature Materials 7 (2008) 367.


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