Charge glass in an extended dimer Hubbard model

The charge degrees of freedom in several different organic charge transfer salts display slow or glassy dynamics. To gain insight into this behavior, we obtain the low-energy theory for an extended dimer Hubbard model, considering the occupations of sites on neighboring dimers. We take a classical limit of the resulting effective model of coupled spins and dimers and study it using classical Monte Carlo simulations. We find that frustration induced by intradimer and interdimer interactions leads to glassiness in the charge degrees of freedom in the absence of ordering of the spin degrees of freedom. Our results may have relevance to experimental observations of relaxor ferroelectric behavior in the dynamics of organic charge transfer salts.