Nearly frozen Coulomb liquids

We show that very long range repulsive interactions of a generalized Coulomb-like form \textbf{\textit{V(R) $\sim $ R}}$^{-a}$, with \textbf{\textit{a $<$ d}} (\textbf{\textit{d}}-spatial dimensionality), typically introduce very strong frustration, resulting in extreme fragility of any charge-ordered state. An ``almost frozen'' liquid then survives in a broad dynamical range above the (very low) melting temperature \textbf{\textit{T}}$_{c}$. Using a combination of extended dynamical mean-field theory [1] and Monte Carlo simulations we study classical lattice gas models with such long range interaction, focusing on the behavior at \textbf{\textit{T $>$ T}}$_{c}$. We find that a soft, temperature-dependent pseudo-gap emerges in this regime, reflecting strong short-range correlations that persist above the melting temperature. This ``pseudo-gap'' phase is characterized by unusual insulating-like, but very weakly temperature dependent transport, similar to experimental findings [2] in many low carrier density systems. [1] S.Pankov and V. Dobrosavljevic, Phys. Rev. Lett.\textbf{ 94}, 046402 (2005). [2] K. Lai, W. Pan, D. C. Tsui, S. Lyon, M. Muhlberger, and F. Schaffler, Phys. Rev. B \textbf{75}, 033314 (2007).