"Competition Between Antiferromagnetic and Charge-Density-Wave Order in the Half-Filled Hubbard-Holstein Model"

E.A. Nowadnick: S. Johnston, B. Moritz, R. T. Scalettar,and T. P. Devereaux; Physical Review Letters, 12/10/12.

Additional Authors: S. Johnston, B. Moritz, R. T. Scalettar,and T. P. Devereaux

Abstract:

We present a determinant quantum Monte Carlo study of the competition between instantaneous on-site
Coulomb repulsion and retarded phonon-mediated attraction between electrons, as described by the
two-dimensional Hubbard-Holstein model. At half filling, we find a strong competition between
antiferromagnetism (AFM) and charge-density-wave (CDW) order. We demonstrate that a simple picture
of AFM-CDW competition that incorporates the phonon-mediated attraction into an effective-U Hubbard
model requires significant refinement. Specifically, retardation effects slow the onset of charge order so
that CDWorder remains absent even when the effective U is negative. This delay opens a window where
neither AFM nor CDW order is well established and where there are signatures of a possible metallic
phase.