Effect of photoinduced screening on the spectroscopic signature of exciton-phonon coupling
ACS Photonics(2024)
摘要
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 presence or absence of dynamical screening in a
layered semiconductor. Further, 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.
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