Institut für Physik, Carl von Ossietzky Universität, 26129, Oldenburg, Germany.
Department of Molecular Chemistry & Materials Science, Weizmann Institute of Science, 76100, Rehovot, Israel.
Nat Commun. 2023 Feb 24;14(1):1047. doi: 10.1038/s41467-023-36654-2.
Coupling electromagnetic radiation with matter, e.g., by resonant light fields in external optical cavities, is highly promising for tailoring the optoelectronic properties of functional materials on the nanoscale. Here, we demonstrate that even internal fields induced by coherent lattice motions can be used to control the transient excitonic optical response in CsPbBr halide perovskite crystals. Upon resonant photoexcitation, two-dimensional electronic spectroscopy reveals an excitonic peak structure oscillating persistently with a 100-fs period for up to ~2 ps which does not match the frequency of any phonon modes of the crystals. Only at later times, beyond 2 ps, two low-frequency phonons of the lead-bromide lattice dominate the dynamics. We rationalize these findings by an unusual exciton-phonon coupling inducing off-resonant 100-fs Rabi oscillations between 1s and 2p excitons driven by the low-frequency phonons. As such, prevailing models for the electron-phonon coupling in halide perovskites are insufficient to explain these results. We propose the coupling of characteristic low-frequency phonon fields to intra-excitonic transitions in halide perovskites as the key to control the anharmonic response of these materials in order to establish new routes for enhancing their optoelectronic properties.
将电磁辐射与物质耦合，例如通过外部光学腔中的共振光场，是在纳米尺度上调整功能材料光电性能的极具前景的方法。在这里，我们证明了即使是由相干晶格运动引起的内部场，也可以用于控制 CsPbBr 卤化物钙钛矿晶体中的瞬态激子光学响应。在共振光激发下，二维电子光谱揭示了一个激子峰结构，以 100fs 的周期持续振荡长达~2ps，这与晶体的任何声子模式的频率都不匹配。只有在 2ps 之后的后期，铅溴晶格的两个低频声子才主导动力学。我们通过一种不寻常的激子-声子耦合来解释这些发现，这种耦合在由低频声子驱动的 1s 和 2p 激子之间诱导了非共振的 100fs Rabi 振荡。因此，卤化物钙钛矿中电子-声子耦合的流行模型不足以解释这些结果。我们提出将特征低频声子场耦合到卤化物钙钛矿中的内激子跃迁作为控制这些材料非谐响应的关键，以建立增强其光电性能的新途径。
