Orientational order in A3C60: Effects on valence bands and infrared optical spectra.

A.I.Liechtenstein, I.I.Mazin, O.Gunnarsson, O.K.Andersen, S.E.Burkov, and V.P.Antropov
Max-Planck-Institut für Festkörperforschung, Stuttgart

By analysis of the electronic contribution to the binding in A3C60, we show that the problem of orientational ordering can be mapped onto the fcc nearest-neighbor antiferromagnetic Ising model with J of the order of 100K. The ground state crystal structure should be therefore antiferromagnetically ordered in two dimensions and disordered in the third. This is not inconsistent with present X-ray powder data. We find that the low-temperature conduction-band structure closely resembles that of the simplest antiferromagnetically ordered (so-called bi-directional) crystal. Calculated optical conductivity can be fitted by a Drude-like contribution and an ``interband'' Lorenzian peak at 400-500 cm^-1.

Electronic Properties of Fullerenes, Eds. H. Kuzmany, J. Fink, M. Mehring, and S. Roth, Springer Series in Solid State Sciences 117, Springer, Berlin, 1993, p. 211.

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