长寿命相干声子揭示$\alpha$-In$_{2}$Se$_{3}$中热与多体动力学的竞争
Long-lived Coherent Phonons Reveal Competing Thermal and Many-Body Dynamics in $α$-In$_{2}$Se$_{3}$
AI总结：
利用飞秒瞬态光栅光谱和第一性原理计算，研究了$\alpha$-In$_{2}$Se$_{3}$中长寿命相干声子，揭示晶格相干性与热及多体相互作用的竞争机制。
AI中文摘要：
光激发后量子相干性的命运是非平衡凝聚态物理中的一个核心问题，尤其是在电子、结构和多体能级强耦合的低维固体中。这里，我们利用约5飞秒激光脉冲的宽带瞬态光栅光谱研究了铁电$\alpha$-In$_{2}$Se$_{3}$中的这种相互作用。光激发引发显著的振荡，主要由约104 cm$^{-1}$模式主导，该模式持续数皮秒。从10到300 K的测量表明，其频率几乎不变，而相干性逐渐被抑制，从而将晶格坐标与热激活的退相区分开来。改变激发能量揭示了一个明显的交叉，其中增加的光激发逐渐改变并阻尼相干响应。第一性原理计算将主导振荡归属于涉及集体In-Se位移的101.47 cm$^{-1}$ $\Gamma$点光学声子，而量子动力学模拟重现了主要的瞬态光栅振荡。这些结果确立了$\alpha$-In$_{2}$Se$_{3}$作为独立探测晶格相干性、热涨落和载流子密度依赖相互作用的模型系统，揭示了极性范德华半导体在超快激发后如何从相干晶格运动演变为非相干多体态。
英文摘要：
The fate of quantum coherence following photoexcitation is a central problem in nonequilibrium condensed-matter physics, especially in low-dimensional solids where electronic, structural and many-body energy scales are strongly coupled. Here, we investigate this interplay in ferroelectric $α$-In$_{2}$Se$_{3}$ using broadband transient-grating spectroscopy with $\sim$5 fs laser pulses. Photoexcitation launches pronounced oscillations dominated by a $\sim$104 cm$^{-1}$ mode that persists for several picoseconds. Measurements from 10 to 300 K show that its frequency remains nearly unchanged while its coherence is progressively suppressed, distinguishing the lattice coordinate from thermally activated dephasing. Varying excitation energy reveals a distinct crossover in which increasing photoexcitation progressively modifies and damps the coherent response. First-principles calculations assign the dominant oscillation to a 101.47 cm$^{-1}$ $Γ$-point optical phonon involving collective In-Se displacement, while quantum-dynamical simulations reproduce the main transient-grating oscillations. These results establish $α$-In$_{2}$Se$_{3}$ as a model system for independently probing lattice coherence, thermal fluctuations and carrier-density-dependent interactions, revealing how a polar van der Waals semiconductor evolves from coherent lattice motion toward an incoherent many-body state after ultrafast excitation.
