Low-Temperature Dielectric Anomaly Arising from Electronic Phase Separation at the Mott Insulator-Metal Transition*

Coulomb repulsion among conduction electrons in solids hinders their motion and leads to a rise in resistivity. A regime of electronic phase separation is expected at the first-order phase transition between a correlated metal and a paramagnetic Mott insulator, but remains unexplored experimentally as well as theoretically nearby T=0. We approach this issue by assessing the complex permittivity via dielectric spectroscopy, which provides vivid mapping of the Mott transition and deep insight into its microscopic nature. Our experiments utilizing physical pressure and chemical substitution consistently reveal a strong enhancement of the quasi-static dielectric constant ε₁ when correlations are tuned through the critical value. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory. Our findings suggest a similar ’dielectric catastrophe’ in many other correlated materials and explain previous observations that were assigned to multiferroicity or ferroelectricity.