The Disorder-Free Non-BCS Superconductor Cs3C60 Emerges from an Antiferromagnetic Insulator Parent State
Yasuhiro Takabayashi,1*
Alexey Y. Ganin,2*
Peter Jegli
,3
Denis Aron,3,4
Takumi Takano,5
Yoshihiro Iwasa,5
Yasuo Ohishi,6
Masaki Takata,6,7
Nao Takeshita,8
Kosmas Prassides,1
Matthew J. Rosseinsky2
The body-centered cubic A15-structured cesium fulleride Cs
3C
60 is not superconducting at ambient pressure and is free from
disorder, unlike the well-studied face-centered cubic A
3C
60 alkali metal fulleride superconductors. We found that in Cs
3C
60,
where the molecular valences are precisely assigned, the superconducting
state at 38 kelvin emerges directly from a localized electron
antiferromagnetic insulating state with the application of pressure.
This transition maintains the threefold degeneracy of the active
orbitals in both competing electronic states; it is thus a purely
electronic transition to a superconducting state, with a dependence
of the transition temperature on pressure-induced changes of
anion packing density that is not explicable by Bardeen-Cooper-Schrieffer
(BCS) theory.
2 Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK.
3 Institute Jo
ef Stefan, Jamova 39, 1000 Ljubljana, Slovenia.
4 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia.
5 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
6 Japan Synchrotron Radiation Research Institute, SPring-8, Hyogo 679-5198, Japan.
7 RIKEN SPring-8 Center, Hyogo 679-5148, Japan.
8 Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8562, Japan.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: k.prassides{at}durham.ac.uk (K.P.); m.j.rosseinsky{at}liverpool.ac.uk (M.J.R.)
