The strength of the electron-phonon interaction
has been addressed in several ways, both via ab initio
alculations and via analysis of experiment.
A very early theoretical estimate was obtained within the
rigid muffin-tin approximation (I.I. Mazin et. al, Phys. Rev.
B 45, 5114 (1992)), using an empirical phonon model.
Later a full potential LMTO calculation was performed to obtain
ab initio phonon frequencies, eigenvectors and electron-phonon
couplings
(Phys. Rev. B 48, 7651 (1993)))
in a frozen phonon approach.
The electron-phonon coupling has also been deduced from
photoemission measurements
for free, negatively charged, C60 molecule.
In this approach the coupling strengths are deduced from the
weights of the phonon satellites in the photoemission spectrum
(Phys. Rev. Lett. 47, 1875 (1995)).
The electron-phonon coupling can also be deduced from Raman
scattering data. These estimates differ substantially from
the once deduced from photoemission. We have therefore
analyzed the methods for extracting the electron-phonon
coupling from Raman scattering data
and shown that the two types of experiment can be partly
reconciled.
To obtain the electron-phonon coupling, it is important to also
know the density of states, since this
quantity enters as a multiplying factor. Different estimates
of density of states have therefore been
analyzed.
The theoretical estimates generally give a rather weak coupling to
the low-lying Hg phonons in contradiction
to the experimental estimates. The reason for this discrepance
is not known.
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