Pressure Evolution of Ultrafast Photocarrier Dynamics and Electron–Phonon Coupling in FeTe(0.5)Se(0.5)

Understanding the coupling between electrons and phonons in iron chalcogenides FeTe [Formula: see text] Se [Formula: see text] has remained a critical but arduous project in recent decades. The direct observation of the electron–phonon coupling effect through electron dynamics and vibrational properties has been lacking. Here, we report the first pressure-dependent ultrafast photocarrier dynamics and Raman scattering studies on an iron chalcogenide FeTe [Formula: see text] Se [Formula: see text] to explore the interaction between electrons and phonons in this unconventional superconductor. The lifetime of the excited electrons evidently decreases as the pressure increases from 0 to 2.2 GPa, and then increases with further compression. The vibrational properties of the [Formula: see text] phonon mode exhibit similar behavior, with a pronounced frequency reduction appearing at approximately 2.3 GPa. The dual evidence reveals the enhanced electron–phonon coupling strength with pressure in FeTe [Formula: see text] Se [Formula: see text]. Our results give an insight into the role of the electron–phonon coupling effect in iron-based superconductors.