CHARGE-DENSITY-WAVE-GAP FORMATION IN THE 2-DIMENSIONAL HOLSTEIN MODELAT HALF-FILLING

We use a combination of quantum Monte Carlo (QMC) methods and analytic continuation techniques to study the formation of charge-density-wave (CDW) gaps at half-filling in the two-dimensional Holstein model. Fro m QMC data for the dressed unequal-time Green's function G(tau,p) we c alculate the real frequency spectral function A (omega, p) for differe nt temperatures T, electron-phonon coupling constants g, phonon freque ncies omega0, and spatial lattice sizes N. We also compute the spectra l functions by approximate diagrammatic methods and find these results to be in good qualitative agreement with the QMC results. We discuss attempts to get quantitative agreement for a range of T and omega0 by using a single renormalized vertex gBAR in place of g, an approach tha t proved useful in previous studies of the Hubbard model. Finally, com parisons are made with previous estimates of the CDW transition temper ature based on measurements of static correlation functions and suscep tibilities.