Transport of quantum excitations coupled to spatially extended nonlinear many-body systems

TL;DR

This study investigates how nonlinear lattice dynamics and different types of exciton-phonon coupling influence quantum excitation transport, revealing non-monotonic temperature dependence and conditions that enhance transport efficiency.

Contribution

It introduces a semi-classical model coupling a tight-binding Hamiltonian with a nonlinear atomic chain, highlighting the effects of nonlinearity and coupling type on transport properties.

Findings

Transport efficiency is enhanced by nonlinearity and off-diagonal coupling at high temperatures.

Exciton diffusion coefficient varies non-monotonically with temperature.

Lattice-induced fluctuations cause non-monotonic temperature dependence of transport.

Abstract

The role of noise in the transport properties of quantum excitations is a topic of great importance in many fields, from organic semiconductors for technological applications to light-harvesting complexes in photosynthesis. In this paper we study a semi-classical model where a tight-binding Hamiltonian is fully coupled to an underlying spatially extended nonlinear chain of atoms. We show that the transport properties of a quantum excitation are subtly modulated by (i) the specific type (local vs non-local) of exciton-phonon coupling and by (ii) nonlinear effects of the underlying lattice. We report a non-monotonic dependence of the exciton diffusion coefficient on temperature, in agreement with earlier predictions, as a direct consequence of the lattice-induced fluctuations in the hopping rates due to long-wavelength vibrational modes. A standard measure of transport efficiency confirms that both nonlinearity in the underlying lattice and off-diagonal exciton-phonon coupling promote transport efficiency at high temperatures, preventing the Zeno-like quench observed in other models lacking an explicit noise-providing dynamical system.