Optical conductivity in the t-J-Holstein Model

TL;DR

This paper investigates the optical conductivity of the t-J-Holstein model, revealing how electron-phonon interactions influence charge dynamics and produce characteristic spectral features linked to magnetic and lattice excitations.

Contribution

It introduces a numerical method to analyze the t-J-Holstein model, uncovering non-monotonous charge stiffness behavior and explaining the origin of two-peak optical spectra.

Findings

Charge stiffness varies non-monotonously with exchange coupling.

Optical conductivity exhibits a two-peak structure.

Peaks are linked to magnetic and lattice excitations.

Abstract

Using recently developed numerical method we compute charge stiffness and optical conductivity of the t-J model coupled to optical phonons. Coherent hole motion is most strongly influenced by the electron-phonon coupling within the physically relevant regime of the exchange interaction. We find unusual non-monotonous dependence of the charge stiffness as a function of the exchange coupling near the crossover to the strong electron-phonon coupling regime. Optical conductivity in this regime shows a two-peak structure. The low-frequency peak represents local magnetic excitation, attached to the hole, while the higher-frequency peak corresponds to the mid infrared band that originates from coupling to spin-wave excitations, broadened and renormalized by phonon excitations. We observe no separate peak at or slightly above the phonon frequency. This finding suggests that the two peak structure seen in recent optical measurements is due to magnetic excitations coupled to lattice degrees of freedom via doped charge carriers.