DYNAMICAL PROPERTIES OF 2 COUPLED HUBBARD CHAINS AT HALF-FILLING

Using grand canonical quantum Monte Carlo (QMC) simulations combined w ith maximum entropy analytic continuation, as well as analytical metho ds, we examine the one- and two-particle dynamical properties of the H ubbard model on two coupled chains at half-filling. The one-particle s pectral weight function, A(k,omega), undergoes a qualitative change wi th interchain hopping t(perpendicular to) associated with a transition from a four-band insulator to a two-band insulator. A simple analytic al model based on the propagation of exact rung singlet states gives a good description of the features at large t(perpendicular to). For sm aller t(perpendicular to), A(k, omega) is similar to that of the one-d imensional model, with a coherent band of width the effective antiferr omagnetic exchange J which is reasonably well described by renormalize d spin-wave theory. The coherent band rides on a broad background of w idth several times the parallel hopping integral t, an incoherent stru cture similar to that found in calculat tions on both the one- and two -dimensional models. We also present QMC results for the two-particle spin and charge excitation spectra, and relate their behavior to the r ung singlet picture for large t(perpendicular to) and to the results o f spin-wave theory for small t(perpendicular to).