, and pressure-induced phonon bottleneck effect*

We conceive and construct an on-site in situ high-pressure time-resolved ultrafast optical spectroscopy instrument [1] that facilitates ultrafast pump-probe dynamics measurements under high pressure conditions. We integrate an ultrafast pump-probe spectroscopy system with a diamond anvil cell (DAC) system. Significantly, both the DAC and the sample are fixed within the light path without motion and rotation throughout the whole experiment, including tuning and calibrating the pressure. This instrument thus avoids introducing artifacts due to sample motion or rotation, enabling precision high-pressure ultrafast pump-probe dynamics investigations. Our data and analysis show that conventional possible artifacts are greatly reduced by using the on-site in situ layout. We also demonstrate a time-resolved ultrafast dynamics study [2] on non-equilibrium quasiparticle (QP) states in Sr₂IrO₄ under high pressure by using this instrument. The QP dynamics exhibits a salient pressure-induced phonon bottleneck feature at 20 GPa, which corresponds to a gap shrinkage in the electronic structure.

Our work helps the high-pressure ultrafast science investigation develop into a promising new area, which enables the exploration of nonequilibrium excited quantum states in the high-pressure regime. Our work enables precise pressure dependence investigations of ultrafast dynamics, paving the way for reliable studies of high-pressure excited state physics.