Marginal quantum criticality of metal-insulator transitions

Abstract Critical exponents of metal-insulator transitions are studied for an extended Hubbard model within the Hartree-Fock approximation. At zero temperature, we find that the first-order transition line between a symmetry broken (antiferromagnetic or charge-ordered) metal and an insulator terminates at the “ marginally quantum critical point ”, where an unconventional universality class emerges. This universality is in agreement with the scaling theory and explains the exponents obtained by recent experiments on ( V , Cr ) 2 O 3 and κ - ( ET ) 2 Cu ( Cn ) 2 Cl in a unified way as a crossover from the marginally quantum universality and the Ising universality.