Electromagnetic field assisted exciton diffusion in moiré superlattices

A. M. Shentsev, M. M. Glazov
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Abstract

We study exciton energy spectrum and their propagation in moir\'e superlattices formed in transition metal dichalcogenide heterobilayers. In such structures, as a result of weak interlayer interaction, an effective, moir\'e, potential acting on excitons arises. Usually, excitons are considered to be localized in such potential. Here we demonstrate that the coupling of optically active excitons with induced electromagnetic field produces linear in the wavevector energy dispersion even if the quantum mechanical tunneling between the localization sites is suppressed. The effect can be described as a result of the processes of virtual generation-recombination of excitons at the localization sites that results in the $ r^{-3}$ dependence of the transfer matrix element on the intersite distance $r$. Based on the calculated energy spectrum we study exciton propagation in moir\'e superlattices with allowance for the light-exciton interaction. We consider semiclassical diffusion of excitons and take into account exciton-phonon and exciton-static defect scattering. For these mechanisms the diffusion coefficient decreases with increase of the temperature. We also analyze the hopping propagation regime and demonstrate that the temperature dependence of the exciton diffusion coefficient is described by the power-law rather than by an exponential function of the temperature.
摩尔纹超晶格中的电磁场辅助激子扩散
我们研究了激子能谱及其在过渡金属二卤化物异质层中形成的摩尔超晶格中的传播。在这种结构中,由于微弱的层间相互作用,会产生作用于激子的有效摩尔势。通常情况下,激子被认为是在这种电势中定位的。在这里,我们证明了光学活性激子与诱导电磁场的耦合会产生线性的波矢能量弥散,即使局域化位点之间的量子力学隧道效应被抑制。这种效应可被描述为局域位点上激子虚拟生成-再组合过程的结果,它导致了转移矩阵元素对位点间距 $r$ 的 $ r^{-3}$ 依赖性。根据计算得到的能谱,我们研究了激子在 Moir\'e 超晶格中的传播,并考虑了光与激子的相互作用。我们考虑了激子的半经典扩散,并将激子-声子散射和激子-静态缺陷散射考虑在内。对于这些机制,扩散系数会随着温度的升高而减小。我们还分析了跳跃传播机制,并证明激子扩散系数的温度依赖性是由幂律而不是温度的指数函数来描述的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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