All-optical manipulation of charge density waves in kagome metal CsV3Sb5

A major challenge in condensed matter physics is to manipulate collective quantum phases by all-optical methods, which can open enormous new possibilities for materials and device engineering. Here we report an anomalous optical modulation of charge density waves (CDWs) in recently discovered kagome metal $\mathrm{Cs}{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ using femtosecond-resolved coherent phonon spectroscopy. This optically suppressed CDW phase surprisingly persists for nanoseconds, exhibits a monotonically lowering of transition temperature with increasing fluence, and does not require a critical absorbed photon density, which is intriguingly distinct from those found in the ``optically suppressed potential energy'' scenario. Pump-pump-probe experiments conclusively rule out the laser-induced thermal effect and time-dependent density functional theory simulations confirm that this nonthermal modulation stems from an optical tuning of the energy resonance between the band fermiology and the Van Hove singularity in kagome lattices. These findings open exciting prospects for all-optical engineering of the Van Hove scenario to tune correlated quantum phases in topology networks.