Andersen Group | El.-Phon. | QMC | C60 | GW | Resistivity saturation |
Electron density of states |
The density of states is an important quantity, not least for
determining the electron-phonon coupling, since it enters as
a multiplying factor in the dimensionless coupling constant
lambda. Widely different
estimates have been given, ranging between about 5 and 15
states/eV-spin. We have studied two of the estimates derived
from experiment, namely those based on the static susceptibility and
NMR.
The Pauli susceptibility of
the A3C60 compounds has
been calculated for a multi-band Hubbard model, using a
projection Quantum Monte-Carlo method. The many-body enhancement
of the susceptibilty was found to be about a factor of three.
From this enhancement and the experimental susceptibility,
the density of states can be estimated.
The NMR relaxation rate has been calculated
for the alkali-doped Fullerenes. The main contribution is found
to come from the spin-dipolar mechanism and not from the
Fermi-contact mechanism, as had often been assumed in earlier work.
The reult is a substantially larger relaxation rate for a given
density of states. To explain the experimental relaxation rate
one therefore has to assume a substantially smaller density of states
than in earlier work.
The large reductions of the density of states deduced from the susceptibility and the NMR relaxation rate means that these estimates are brought in line with estimates based on the specific heat and band structure results. It was concluded that the density of states is of the order 5-7 states per spin and eV ((Phys. Rev. B 55, R10165 (1997)).
Andersen Group |
Max-Planck-Institut für Festkörperforschung Heisenbergstraße 1 D-70569 Stuttgart |