Ying Wenxiang, Mondal M Elious, Huo Pengfei
Department of Chemistry, University of Rochester, 120 Trustee Road, Rochester, New York 14627, USA.
The Institute of Optics, Hajim School of Engineering, University of Rochester, Rochester, New York 14627, USA.
J Chem Phys. 2024 Aug 14;161(6). doi: 10.1063/5.0225387.
The motional narrowing effect has been extensively studied for cavity exciton-polariton systems in recent decades both experimentally and theoretically, which is featured by (1) the subaverage behavior and (2) the asymmetric linewidths for the upper polariton and the lower polariton. However, a minimal theoretical model that is clear and adequate to address all these effects as well as the linewidth scaling relations remains missing. In this work, based on the single mode 1D Holstein-Tavis-Cummings (HTC) model, we studied the motional narrowing effect of the polariton linear absorption spectra via both semi-analytic derivations and numerically exact quantum dynamics simulations using the hierarchical equations of motion approach. The results reveal that under collective light-matter coupling between a cavity mode and N molecules, the polariton linewidth scales as 1/N under the slow limit, while scales as 1/N under the fast limit, due to the polaron decoupling effect. Furthermore, by varying the detunings, the polariton linewidths exhibit significant motional narrowing, covering both characters mentioned above. Our analytic linewidth expressions [Eqs. (34) and (35)] agree well with the numerical exact simulations in all the parameter regimes we explored. These results indicate that the physics of motional narrowing is adequately accounted for by the single-mode 1D HTC model. We envision that both the numerical results and the analytic polariton linewidths expression presented in this work will offer great theoretical value for providing a better understanding of the exciton-polariton motional narrowing based on the HTC model.
近几十年来，人们对腔激子 - 极化激元系统的运动窄化效应进行了广泛的实验和理论研究，其特点是：（1）亚平均行为；（2）上极化激元和下极化激元的线宽不对称。然而，一个清晰且足以解释所有这些效应以及线宽缩放关系的最小理论模型仍然缺失。在这项工作中，基于单模一维霍斯坦 - 塔维斯 - 卡明斯（HTC）模型，我们通过半解析推导和使用运动方程分层方法的数值精确量子动力学模拟，研究了极化激元线性吸收光谱的运动窄化效应。结果表明，在腔模与N个分子之间的集体光 - 物质耦合下，由于极化子解耦效应，极化激元线宽在慢极限下按1 / N缩放，而在快极限下也按1 / N缩放。此外，通过改变失谐量，极化激元线宽表现出显著的运动窄化，涵盖了上述两种特征。我们的解析线宽表达式[式（34）和（35）]在我们探索的所有参数范围内与数值精确模拟结果吻合良好。这些结果表明，单模一维HTC模型充分考虑了运动窄化的物理机制。我们设想，这项工作中给出的数值结果和解析极化激元线宽表达式将为基于HTC模型更好地理解激子 - 极化激元运动窄化提供巨大的理论价值。
