Nonmonotonic evolution of the charge gap in ZnV2O4 under pressure

A(2+)V(2)O(4) spinels provide a unique opportunity for studying the evolution of the charge gap of Mott insulators that approach the itinerant electron limit under the application of external pressure. Here we report high-pressure resistivity and optical measurements in ZnV2O4 that provide unambiguous evidence of an unusual nonmonotonic behavior of the charge gap, Delta, as a function of pressure P. These unexpected results suggest that ZnV2O4 undergoes a crossover from a Mott insulator with a charge gap dominated by the on-site Coulomb repulsion U, to a second type of insulator in the high pressure regime. Our Monte Carlo simulations of the three-band Hubbard model relevant for ZnV2O4 reproduce the nonmonotonic behavior of Delta(P) and provide a partial understanding of this exotic phenomenon.