Linear and non-linear infrared response of one-dimensional vibrational Holstein polarons in the anti-adiabatic limit: optical and acoustical phonon models

TL;DR

This paper develops a theoretical framework for analyzing the linear and non-linear infrared responses of vibrational Holstein polarons in one-dimensional lattices, revealing spectral signatures of self-trapping and interpreting experimental spectra.

Contribution

It introduces a canonical transformation approach to compute infrared responses for optical and acoustical phonon baths in the anti-adiabatic limit, linking theory with experimental data.

Findings

Linear response probes polaron density of states in optical phonon systems.

Two bound states observed in two-dimensional IR spectra at low temperature.

Bath-mediated correlations influence spectral diffusion at high temperature.

Abstract

The theory of linear and non-linear infrared response of vibrational Holstein polarons in one-dimensional lattices is presented in order to identify the spectral signatures of self-trapping phenomena. Using a canonical transformation the optical response is computed from the small polaron point of view which is valid in the anti-adiabatic limit. Two types of phonon baths are considered: optical phonons and acoustical phonons, and simple expressions are derived for the infrared response. It is shown that for the case of optical phonons, the linear response can directly probe the polaron density of states. The model is used to interpret the experimental spectrum of crystaline actetanilide in the C=O range. For the case of acoustical phonons, it is shown that two bound states can be observed in the two-dimensional infrared spectrum at low temperature. At high temperature, analysis of the time-dependence of the two-dimensional infrared spectrum indicates that bath mediated correlations slow down spectral diffusion. The model is used to interpret the experimental linear-spectroscopy of model alpha-helix and beta-sheet polypeptides. This work shows that the Davydov Hamiltonian cannot explain the observations in the NH stretching range.