The recent identification of strongly bound excitons in room-temperature anatase TiO₂ single crystals and nanoparticles underscores the importance of bulk many-body effects in samples used for applications. Here, for the first time, we unravel the interplay between many-body interactions and correlations in highly excited anatase TiO₂ nanoparticles using ultrafast two-dimensional deep-ultraviolet spectroscopy. With this approach, under nonresonant excitation, we disentangle the optical nonlinearities contributing to the bleach of the lowest direct exciton peak. This allows us to clock the ultrafast time scale of the hot electron thermalization in the conduction band with unprecedented temporal resolution, which we determine to be <50 fs, due to the strong electron–phonon coupling in the material. Our findings call for the design of alternative resonant excitation schemes in photonics and nanotechnology.

中文翻译：

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锐钛矿型钛白粉纳米颗粒中超快电子冷却的计时

最近在室温锐钛矿型TiO ₂单晶和纳米颗粒中强结合激子的鉴定突出了在应用样品中体多体效应的重要性。在这里，我们首次揭示了高激发锐钛矿型TiO _2的多体相互作用与相关性之间的相互作用。使用超快二维深紫外光谱法分析纳米颗粒。通过这种方法，在非共振激发下，我们解开了光学非线性，从而造成了最低直接激子峰的漂白。这使我们能够以前所未有的时间分辨率记录导带中热电子热化的超快时间标度，由于材料中强的电子-声子耦合，我们确定其小于50 fs。我们的发现要求设计光子学和纳米技术中的替代共振激发方案。