CDW FORMATION IN ELECTRON-PHONON SYSTEMS
    We used Quantum Monte Carlo to study a simple two-dimensional electron-phonon model.[1] At half filling, a Peierls-Charge Density Wave (CDW) instability was found to dominate the behavior of the system and to suppress superconductivity. The CDW structure factor scaled with system size and is consistent with a finite size Ising-like scaling analysis which we used to estimate Tc for the Peierls-CDW transition. Away from half filling, the Monte Carlo calculations show superconducting pairing in an s-wave channel, with a peak in the pair field susceptibility near a region in which there are strong Peierls-CDW correlations.

    We also used 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 2-dimensional Holstein model.[2] >From QMC data for the dressed unequal time Green's function G(tau,p) we calculate the real frequency spectral function A(omega,p) for different temperatures T, electron-phonon coupling constants g, phonon frequencies omega0, and spatial lattice sizes N. We also computed the spectral functions by approximate diagrammatic methods and found these results to be in good qualitative aggreement with the QMC results. We discussed attempts to get quantitative agreement for a range of T, omega0 by using a single renormalized vertex gbar in place of g, an approach that proved useful in previous studies of the Hubbard model. Finally, comparisons were made with previous estimates of the CDW transition temperature based on measurements of static correlation functions and susceptibilities.

    Relevant Publications:

    [31.] "CDW and Pairing Susceptibilities in a Two Dimensional Electron-Phonon Model," R.M. Noack, D.J. Scalapino, and R.T. Scalettar, Phys. Rev. Lett. 66, 778 (1991).

    [47.] "Charge Density Wave Gap Formation in the 2-dimensional Holstein Model at Half-Filling," P. Niyaz, J.E. Gubernatis, R.T. Scalettar, and C. Y. Fong, Phys. Rev. B48, 16011 (1993).

    [75.] "Variational Monte Carlo Study of an Interacting Electron-Phonon Model", B.J. Alder, K.J. Runge, and R.T. Scalettar, Phys. Rev. Lett. 79, 3022 (1997).