Charge and spin dynamics of the two-dimensionaltmodel in leading order of a 1/Nexpansion

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Abstract
The density- and spin-correlation functions of the t model are calculated on a square lattice in leading order of a 1/N expansion using X operators and a Baym-Kadanoff expansion. While the spectra of both correlation functions are similar at low densities, the energy scale for density fluctuations becomes much higher than that of spin fluctuations at large densities, due to collective effects. Our results agree quite well with recent exact diagonalizations for the case N=2. Furthermore, we examine the idea that the charge correlations of strongly correlated electrons with spin can be described by those of uncorrelated spinless electrons in two dimensions. While the equal-time density correlation functions of both systems are similar, the dynamic ones behave quite differently at high densities.

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