Cluster approach study of intersite electron correlations in pyrochlore and checkerboard lattices

Abstract

To treat effects of electron correlations in geometrically frustrated pyrochlore and checkerboard lattices, an extended single-orbital Hubbard model with nearest-neighbor hopping ∼t and Coulomb repulsion ∼V is applied. Infinite on-site repulsion, U→∞, is assumed, thus double occupancies of sites are forbidden completely in the present study. A variational Gutzwiller-type approach is extended to examine correlations due to short-range V interaction and a cluster approximation is developed to evaluate a variational ground-state energy of the system. Obtained analytically in a special case of quarter band filling appropriate to LiV2O4, the resulting simple expression describes the ground-state energy in the regime of intermediate and strong coupling V. Like in the Brinkman-Rice theory based on the standard Gutzwiller approach to the Hubbard model, the mean value of the kinetic energy is shown to be reduced strongly as the coupling V approaches a critical value Vc. This finding may contribute to explaining the observed heavy fermion behavior in LiV2O4