Field Theory equations on nearly real frequency axis : new insight into the nature of metal - insulator transition

The Iterated Perturbation Theory (IPT) equations of the Dynamical Mean Field Theory (DMFT) for the half-filled Hubbard model, are solved on nearly real frequencies at various values of the Hubbard parameters U , to investigate the nature of metal-insulator transition (MIT) at finite temperatures. This method avoids the instabilities associated with the infamous Padé analytic continuation and reveals fine structures across the MIT at finite temperatures, which can not be captured by conventional methods for solving DMFT equations on Matsubara frequencies. Our method suggests that at finite temperatures, there is an abrupt decrease in the height of the quasi-particle (Kondo) peak at a critical value of Uc, to a non-zero but small bump which gradually suppresses as one moves deeper into the bad insulator regime. In contrast to Vollhardt and coworkers [J. Phys. Soc. Jpn. 74 (2005) 136], down to T = 0.01 of the half-bandwidth we find no T ∗ separating bad insulator from a true Mott insulator.