Centre for Theoretical Physics and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
J Chem Phys. 2013 Jun 7;138(21):214316. doi: 10.1063/1.4808155.
We study the transport of collective excitations (Frenkel excitons) in systems with static disorder in the transition energies, not limiting ourselves to Gaussian transition energy distributions. Instead, we generalize this model to the wider class of Lévy stable distributions, characterized by heavy tails. Phonon-assisted scattering of excitons, localized by the disorder, leads to thermally activated exciton motion. The time evolution of the second moment of the exciton distribution is shown to be sublinear, thus indicating that the exciton dynamics in such systems is not diffusive, but rather subdiffusive instead. The heavier the tail in the transition energy distribution is, the larger are the deviations from the diffusive regime. This from fluctuations of site energies larger than the exciton band width (outliers). We show that the occurrence of subdiffusive transport for heavy-tailed disorder distributions can be understood from the scattering rate distributions, which possess a (second) peak at zero scattering rate.
我们研究了在跃迁能量存在静态无序的系统中集体激发（弗伦克尔激子）的输运，而不局限于高斯跃迁能量分布。相反，我们将该模型推广到更广泛的 Lévy 稳定分布类，其特征是尾部较重。由无序局域化的声子辅助激子散射导致热激活激子运动。激子分布的二阶矩的时间演化被证明是次线性的，从而表明此类系统中的激子动力学不是扩散的，而是次扩散的。跃迁能量分布中的尾部越重，偏离扩散态的程度就越大。这是由于局域能的涨落大于激子能带宽度（异常值）。我们表明，对于重尾无序分布，次扩散输运的发生可以从散射率分布中得到理解，该分布在零散射率处具有（二次）峰值。
