Structure of Haloform Intercalated C60 and Its Influence on Superconductive Properties
Robert E. Dinnebier,1
Olle Gunnarsson,1
Holger Brumm,1
Erik Koch,1
Peter W. Stephens,2
Ashfia Huq,2
Martin Jansen1*
CHCl3 and CHBr3 intercalated
C60 have attracted particular interest after a
superconductivity transition temperature (Tc) of
up to 117 K was discovered. We have determined the structure using
synchrotron x-ray powder-diffraction and found that the expansion of
the lattice mainly takes place in one dimension (triclinic b
axis), leaving planes of C60 molecules on an approximately
hexagonal, slightly expanded lattice. We have performed tight-binding
band structure calculations for the surface layer. In spite of
the slight expansion of the layers, for the range of dopings where a
large Tc has been observed, the density of
states at the Fermi energy is smaller for
C60·2CHCl3 and
C60·2CHBr3 than for C60. This
suggests that the lattice expansion alone cannot explain the increase
of Tc.
1 Max-Planck-Institut für
Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart,
Germany.
2 Department of Physics and Astronomy,
State University of New York, Stony Brook, NY 11974, USA.
*
To whom correspondence should be addressed. E-mail:
m.jansen{at}fkf.mpg.de
