Nonadiabatic approach to dimerization gap and optical absorption coefficient of the Su-Schrieffer-Heeger model

TL;DR

This paper presents an analytical nonadiabatic approach to study how quantum phonon fluctuations affect the dimerization gap and optical absorption in the Su-Schrieffer-Heeger model, aligning well with experimental data.

Contribution

It introduces a novel nonadiabatic analytical method to analyze quantum phonon effects on electronic properties in the SSH model, emphasizing the impact of lattice fluctuations.

Findings

Quantum phonon fluctuations significantly reduce the dimerization gap.

Optical absorption spectrum peaks above the gap edge without inverse-square-root singularity.

Results agree with experimental optical spectra in shape and peak position.

Abstract

An analytical nonadiabatic approach has been developed to study the dimerization gap and the optical absorption coefficient of the Su-Schrieffer-Heeger model where the electrons interact with dispersive quantum phonons. By investigating quantitatively the effects of quantum phonon fluctuations on the gap order and the optical responses in this system, we show that the dimerization gap is much more reduced by the quantum lattice fluctuations than the optical absorption coefficient is. The calculated optical absorption coefficient and the density of states do not have the inverse-square-root singularity, but have a peak above the gap edge and there exist a significant tail below the peak. The peak of optical absorption spectrum is not directly corresponding to the dimerized gap. Our results of the optical absorption coefficient agree well with those of the experiments in both the shape and the peak position of the optical absorption spectrum.