Nonequilibrium dynamics in pumped excitonic insulators

Applying optical pulses on insulators provides us with a new route to realize an insulator-to-metal transition, which can be observed by time-resolved spectroscopy experiments.

In (quasi-)one dimension, such nonequilibrium dynamics can be simulated by the time-dependent density-matrix renormalization group technique with so-called infinite boundary conditions. In this talk, we demonstrate a photoinduced metallization of excitonic insulators by applying this unbiased numerical technique to the extended Falicov-Kimball model (EFKM) both with and without the internal SU(2) structure. In the SU(2)-symmetric case, an extra band appears above Fermi energy after pulse irradiation, reflecting the enhanced electron-electron pair correlations. Even in the absence of the SU(2) structure, the pair correlations can be enhanced transiently by optimizing the pump parameters. This implies the possible metallization of Ta₂NiSe₅, a strong candidate for an excitonic insulator, whose minimal model is considered to be the EFKM without internal SU(2) symmetry. This photoinduced insulator-to-metal transition reflects recent findings in time-resolved photoemission spectroscopy experiments on Ta₂NiSe₅.