Polymorphism control of superconductivity and magnetism in Cs3C60 close to the Mott transition

• Published in: Nature (London) 2010-07, Vol.466 (7303), p.221-225
• Main Authors: Ganin, Alexey Y., Takabayashi, Yasuhiro, Jeglič, Peter, Arčon, Denis, Potočnik, Anton, Baker, Peter J., Ohishi, Yasuo, McDonald, Martin T., Tzirakis, Manolis D., McLennan, Alec, Darling, George R., Takata, Masaki, Rosseinsky, Matthew J., Prassides, Kosmas
• Format: Article
• Language: English
• Subjects: 639/301/119/1003; 639/301/119/997; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states; Exact sciences and technology; Humanities and Social Sciences; letter; Magnetic properties; Metal-insulator transitions and other electronic transitions; multidisciplinary; Physics; Properties of type I and type II superconductors; Science; Science (multidisciplinary); Superconductivity
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature09120

Superconducting crystal balls Superconductivity and magnetic order are well known in C 60 compounds of the form A 3 C 60 (where A is an alkali metal). The spherical C 60 molecular ions in these superconducting crystals are almost exclusively arranged in a face-centred cubic lattice; the one exception is Cs 3 C 60 , where the known superconducting phase has a body-centred cubic packing. Now Ganin et al . have isolated the face-centred cubic polymorph of Cs 3 C 60 , and show that it too is superconducting, although its magnetic properties are very different from its body-centred cubic counterpart. The identification of these two distinct superconducting crystal structures in the same material should help to elucidate the nature of the subtle interplay between structure, magnetism and superconductivity in this and other high-temperature superconducting systems. Superconductivity and magnetic order are well known in C 60 compounds of the form A 3 C 60 (where A = alkali metal). The spherical C 60 molecular ions in these crystals are almost always arranged in a face-centred cubic (f.c.c.) packing, except in Cs 3 C 60 , where the known superconducting phase has a body-centred cubic (b.c.c) packing. Now the f.c.c. polymorph for Cs 3 C 60 has been isolated; it too is superconducting, although its magnetic properties are very different to those of its b.c.c counterpart. The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu 2+ units—a two-dimensional square lattice—is available to study the competition between the cooperative electronic states of magnetic order and superconductivity 1 . Crystals of the spherical molecular C 60 3- anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A 3 C 60 (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C 60 3- (refs 2 , 3 ), but recently the most expanded (and thus having the highest superconducting transition temperature, T c ; ref. 4 ) composition Cs 3 C 60 has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order 5 , 6 . Here we isolate the f.c.c. polymorph of Cs 3 C 60 to show how the spatial arrangement of the