Abstract
Ground state properties of multi-orbital Hubbard models areinvestigated by the auxiliary field quantum Monte Carlo method.A Monte Carlo technique generalizedto the multi-orbital systems is introduced and examined in detail.The algorithm contains non-trivial cases wherethe negative sign problem does not exist.We investigate one-dimensional systemswith doubly degenerate orbitals by this new technique.Properties of the Mott insulating state are quantitativelyclarified as the strongly correlated insulator, where the charge gap amplitude is much larger than the spin gap.The insulator-metal transitions drivenby the chemical potential shows a universality classwith the correlation length exponent ν=1/2, which is consistent with the scaling arguments.Increasing level split between two orbitals drives crossoverfrom the Mott insulator with high spin state tothe band insulator with low spin state, where the spin gap amplitude increases and becomes closer to the charge gap.Experimental relevance of our resultsespecially to Haldane materials is discussed.
