We use determinant quantum Monte Carlo to study the single-particle properties of quasiparticles and phonons in a variant of the two-dimensional Holstein model that includes an additional nonlinear electron-phonon (e-ph) interaction. We find that a small positive nonlinear interaction reduces the effective coupling between the electrons and the lattice, suppresses charge-density-wave (CDW) correlations, and hardens the effective phonon frequency. Conversely, a small negative nonlinear interaction can enhance the e-ph coupling resulting in heavier quasiparticles, an increased tendency towards a CDW phase at all fillings, and a softened phonon frequency. An effective linear model with a renormalized interaction strength and phonon frequency can qualitatively capture this physics; however, the quantitative effects of the nonlinearity on both the electronic and phononic degrees of freedom cannot be captured by such a model. These results are significant for typical nonlinear coupling strengths found in real materials, indicating that nonlinearity can have an important influence on the physics of many e-ph coupled systems.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Aug 3 2015|
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics