The light-mediated interaction of fermionic and bosonic excitations governs the optoelectronic properties of condensed matter systems. In photoexcited semiconductors, the coupling of electron–hole pairs (excitons) to coherent optical phonons enables a modulation of the excitonic resonance that is phase-locked to the frequency of the coupled vibrational mode. Moreover, due to the Coulombic nature of excitons, their dynamics are sensitive to transient changes in the screening by the photoexcited carriers. Interestingly, the effect of photoinduced screening on the transient optical signal originating from the exciton dynamics coupled to phonons is not yet established. By means of broadband transient reflectance spectroscopy, we disclose how exciton–phonon coupling manifests in either the presence or absence of dynamical screening in a layered semiconductor. Furthermore, we unveil the promoting role of photoinduced screening on these exciton–phonon coupled dynamics as opposed to the case in which the unscreened exciton–exciton repulsion likely dominates the nonequilibrium optical response. These findings set a protocol to look at an excitonic resonance and its fundamental many-body interactions on the ultrafast timescale and provide new perspectives on the access to nonequilibrium coupled dynamics.

中文翻译：

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光诱导筛选对激子-声子耦合光谱特征的影响


费米子和玻色子激发的光介导相互作用控制着凝聚态物质系统的光电特性。在光激发半导体中，电子空穴对（激子）与相干光学声子的耦合能够实现激子共振的调制，该激子共振与耦合振动模式的频率锁相。此外，由于激子的库仑性质，它们的动力学对光激发载流子屏蔽的瞬态变化敏感。有趣的是，光诱导屏蔽对源自与声子耦合的激子动力学的瞬态光信号的影响尚未确定。通过宽带瞬态反射光谱，我们揭示了激子-声子耦合在层状半导体中存在或不存在动态屏蔽时如何表现。此外，我们揭示了光诱导屏蔽对这些激子-声子耦合动力学的促进作用，而不是未屏蔽的激子-激子排斥可能主导非平衡光学响应的​​情况。这些发现制定了一个协议来研究激子共振及其在超快时间尺度上的基本多体相互作用，并为获得非平衡耦合动力学提供了新的视角。