Crossover from Super- to Sub-Diffusive Motion and Memory Effects in Crystalline Organic Semiconductors

TL;DR

This study investigates charge transport in crystalline organic semiconductors, revealing a temperature-induced crossover from super- to sub-diffusive motion and highlighting the role of memory effects and electron-lattice interactions.

Contribution

The paper introduces a combined computational approach to accurately reproduce experimental mobility data and explains the transport crossover and spectral features in organic semiconductors.

Findings

Crossover from super- to sub-diffusive motion at 150-200 K

Memory effects become significant near the crossover temperature

An effective model explains low-frequency absorption spectra

Abstract

The transport properties at finite temperature of crystalline organic semiconductors are investigated, within the Su-Schrieffer-Heeger model, by combining exact diagonalization technique, Monte Carlo approaches, and maximum entropy method. The temperature-dependent mobility data measured in single crystals of rubrene are successfully reproduced: a crossover from super- to sub-diffusive motion occurs in the range $150 \leq T \leq 200$ K, where the mean free path becomes of the order of the lattice parameter and strong memory effects start to appear. We provide an effective model which can successfully explain low frequencies features of the absorption spectra. The observed response to slowly varying electric field is interpreted by means of a simple model where the interaction between the charge carrier and lattice polarization modes is simulated by a harmonic interaction between a fictitious particle and an electron embedded in a viscous fluid.