Finite-temperature charge dynamics and the melting of the Mott insulator*

The Mott insulator is the quintessential strongly correlated electronic state. A full understanding of the coupled charge and spin dynamics of the Mott-insulating state is thought to be the key to a range of phenomena in ultracold atoms and condensed matter, including high-T_c superconductivity. Here we extend the slave-fermion (holon-doublon) description of the two-dimensional Mott insulator to finite temperatures. We benchmark its predictions against state-of-the-art quantum Monte Carlo simulations, finding quantitative agreement. Qualitatively, the short-ranged spin fluctuations at any finite temperatures are sufficient to induce holon-doublon bound states, and renormalize the charge sector to form the Hubbard bands. The Mott gap is understood as the charge (holon-doublon) gap renormalized downwards by these spin fluctuations. With increasing temperature, the Mott gap closes while the charge gap remains finite, causing a pseudogap regime to appear naturally during the process of melting the Mott insulator.