Direct Investigation of Ultrafast Charge Density Wave (CDW) Dynamics in Kagome Metal, Through Time-resolved X-ray Scattering*

Charge Density Wave (CDW) state, broken symmetry state of electronic modulation, plays a crucial role in quantum phases within the intertwined electronic degrees of freedom on lattice playground. Conventionally, Peierls distortion model with nested Fermi surface and soften phonon mode provides a fundamental picture to describe the CDW phase transition with the structural instability driven by strong electron-phonon coupling.

New kagome metal systems ( AV₃Sb₅, A = K, Rb, Cs), which owns exotic electronic structures simultaneously, have been attracting surging attention as an ideal system to investigate the interplay of topology, electron correlations and superconductivity.

CDW in AV₃Sb₅ has two type charge order. One is 2x2x1 charge order that caused by dimerization of vanadium atom and the other is 2x2x2 charge order caused by different distortion pattern in vanadium layer.

Recently, we observed that 2x2x2 and 2x2x1 CDW state using time-resolved X-ray scattering at PAL-XFEL, and have found difference between two charge orders in melting and recover process on sub-picosecond regime. This non-equilibrium dynamics of CDW presents the role of interaction into c axis in CDW and suggests that the A-site ions significantly influence the CDW phase, through a storng electron-phonon coupling mode.