Photo-induced pattern formations and melting of charge-density-wave order

TL;DR

This paper explores how photo-excitation affects charge-density-wave order in a Holstein model, revealing pattern formation, melting, and self-sustained oscillations through large-scale real-time simulations.

Contribution

It introduces a novel real-space dynamical simulation method and uncovers complex pattern formation and dynamical inhomogeneity in photo-excited CDW systems.

Findings

Photo-pulse reduces CDW order and generates coherent phonons.

Strong excitation melts CDW order but sustains a dynamical state with phonon oscillations.

Intermediate fluence induces complex spatial textures and pattern formation.

Abstract

We investigate the out-of-equilibrium dynamics of a photo-excited charge-density-wave (CDW) state in the square-lattice Holstein model, in a setup similar to a pump-probe experiment. At half-filling, the ground state of this system is characterized by a checkerboard modulation of particle densities, accompanied by a concomitant lattice distortion. An efficient real-space dynamics method integrating the von~Neumann equation for electron density matrix and Newton equation for classical lattice dynamics is developed to simulate the dynamical evolution of a photo-excited Holstein system. We find that the energy injected by a short pump pulse results in the reduction of the CDW order and the generation of coherent phonons. At strong photoexcitations, while the CDW order is melted in the sense that the time-averaged order parameter vanishes, a dynamical CDW state is self-sustained by the strong coherent phonon oscillations. Our large-scale simulations further uncover a dynamical regime of intermediate fluence where complex pattern formation is induced by the pump pulse. The emergent spatial textures are characterized by super density modulations on top of the short-range checkerboard CDW order. Our demonstration of pattern formation highlights the significance of dynamical inhomogeneity in quantum many-body systems in pump-probe experiments.