Andersen Group El.-Phon. QMC C60 GW Resistivity saturation

Density of states
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)).

Max-Planck Institut für Festkörperforschung
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