Metal-Insulator transitions in generalized Hubbard models

Erik Koch (a), Olle Gunnarsson (a), and Richard M. Martin (a, b)
(a) Max-Planck-Institut fuer Festkoerperforschung, Stuttgart
(b) Department of Physics, University of Illinois, Urbana-Champaign

We study the Mott transition in Hubbard models with a degenerate band on different 3-dimensional lattices. While for a non-degenerate band only the half-filled system may exhibit a Mott transition, with degeneracy there can be a transition for any integer filling. We analyze the filling dependence of the Mott transition and find that Uc (the Hubbard interaction U at which the transition takes place) decreases away from half-filling. In addition we can change the lattice structure of the model. This allows us to study the influence of frustration on the Mott transition. We find that frustration increases Uc, compared to bipartite systems. The results were obtained from fixed-node diffusion Monte Carlo calculations using trial functions which allow us to systematically vary the magnetic character of the system. To gain a qualitative understanding of the results, we have developed simple hopping arguments that help to rationalize the doping dependence and the influence of frustration on the Mott transition. Choosing the model parameters to describe the doped Fullerides, we can make contact with experiment and understand why some of the Fullerides are metals, while others, which according to density functional theory should also be metallic, actually are insulators.

Proceedings of the CCP99/Centennial Conference of the APS
Computer Physics Communications 127, 137 (2000)

A postscript file is available at this http URL

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