Adiabatic-Nonadiabatic Transition in the Diffusive Hamiltonian Dynamics of a Classical Holstein Polaron

TL;DR

This paper investigates the Hamiltonian dynamics of a classical Holstein polaron, revealing temperature-dependent diffusive behaviors and power-law diffusion constants, with a transition from diffusion to hopping at low temperatures.

Contribution

It introduces a detailed analysis of adiabatic and nonadiabatic transitions in the diffusive dynamics of a classical Holstein polaron, highlighting temperature-dependent regimes and power-law behaviors.

Findings

Diffusive motion with D ~ T^{5/2} at high temperatures.

Hopping process with D ~ T^{3/4} at low temperatures.

Thermally activated diffusion due to self-trapped polaronic states.

Abstract

We study the Hamiltonian dynamics of a free particle injected onto a chain containing a periodic array of harmonic oscillators in thermal equilibrium. The particle interacts locally with each oscillator, with an interaction that is linear in the oscillator coordinate and independent of the particle's position when it is within a finite interaction range. At long times the particle exhibits diffusive motion, with an ensemble averaged mean-squared displacement that is linear in time. The diffusion constant at high temperatures follows a power law D ~ T^{5/2} for all parameter values studied. At low temperatures particle motion changes to a hopping process in which the particle is bound for considerable periods of time to a single oscillator before it is able to escape and explore the rest of the chain. A different power law, D ~ T^{3/4}, emerges in this limit. A thermal distribution of particles exhibits thermally activated diffusion at low temperatures as a result of classically self-trapped polaronic states.