By integrating pump-probe ultrafast spectroscopy with diamond anvil cell (DACs) technique, they successfully realize an on-site in situ time-resolved ultrafast optical spectroscopy instrumentation. Using this novel experimental system, they carried out ultrafast dynamics investigation in Sr₂IrO₄ under high pressure. In their design and construction of the instrument, both the sample and DACs are fixed in the light path during the whole experiment, especially during the tuning and calibration of the high pressure, which greatly enhances the data reliability. Significantly, they find a pressure-induced phonon bottleneck effect, which is new to condensed matter physics. As such, their investigation contributes to initiating a new research area—high pressure ultrafast dynamics, which adds a new dimension to the investigation of condensed matter physics under extreme conditions.

Ultrafast optical spectroscopy and high pressure science are two important fields in condensed matter physics. However, before, there were very few works combining them together. If the DACs are taken out of the light path when tuning and calibrating the pressure, it will potentially produce artifacts due to the sample motion or rotation. Furthermore, it is essential to uncover pressure-induced excited state properties by observing the ultrafast dynamics, whereby the pressure-induced phonon bottleneck effect constitutes such an example.

This study entitled "High-Pressure Ultrafast Dynamics in Sr₂IrO₄: Pressure-Induced Phonon Bottleneck Effect" was published on Chinese Physics Letters (Express Letter) 37, 047801 (2020). The study was supported by the National Key Research and Development Program of China, the Chinese Academy of Sciences, and the National Natural Science Foundation of China.