In the hyperexpanded bcc-structured A15 Cs₃C₆₀, superconductivity emerges upon applied pressure out of an antiferromagnetic insulating state and displays a dome in T_c as a function of the volume per C₆₀^3- anion. Whereas in the high-T_c cuprates, the Cu²⁺ cation is limited to one structural arrangement (a 2D square lattice), we have now isolated a second polymorph of the magnetic and superconducting fulleride Cs₃C₆₀ with an fcc structure. This enables a comparison between these two cooperative electronic states when the same electronically active unit is arranged differently in space. The dominant role of electron correlations is then shown by a simple structure-independent scaling of T_c according to proximity to the correlation-driven Mott metal-insulator transition.

Universal trend in the superconducting transition temperature as a function of the proximity to the Mott transition.
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 ISIS muons were vital in the discovery of spin ordering of the fcc variant, where magnetism is dramatically suppressed by the frustrated nature of the lattice structure.

K Prassides (Durham University), MJ Rosseinsky (University of Liverpool), PJ Baker (ISIS)

Research date: December 2009

Further Information

Contact: Prof K Prassides, K.Prassides@durham.ac.uk

Further information: AY Ganin et al., Nature 466 (2010) 221​