Coherent Phonon Driven Carrier Pumping in Topological Materials

Laser-stimulated coherent phonon as a modulated strain field can modify ground state topological properties of quantum materials. Using real-time time-dependent density functional theory, we show that accompanying the periodic topological switching, carriers can be gradually pumped from valence band to conduction band despite the orders of magnitude smaller of the phonon energy relative to the insulating gap. This is achieved through the Landau-Zener tunnelling in certain region of the irreducible Brillouin zone where the transient energy gap becomes sufficiently small. The simulation results are consistent with the recent pump-probe experiment on the topological insulator ZrTe₅ at low temperature.