Nonequilibrium dynamics in the pump-probe spectroscopy of excitonic insulators

TL;DR

This study investigates how ultrafast pump-probe laser pulses affect excitonic order in insulators, revealing frequency-dependent suppression or enhancement of excitonic condensation in different electronic regimes.

Contribution

It introduces a time-dependent mean-field approach to analyze nonequilibrium excitonic dynamics under laser pulses, highlighting distinct behaviors in BEC and BCS regimes.

Findings

Excitonic order can be suppressed or enhanced depending on pulse frequency in the BEC regime.

Strong pulses can completely destroy excitonic order in the BEC regime.

In the BCS regime, excitonic order is always suppressed regardless of pulse frequency.

Abstract

We study the nonequilibrium dynamics in the pump-probe spectroscopy of excitonic insulators using the spinless two-orbital model with phonon degrees of freedom in the time-dependent mean-field approximation. We introduce the pulse light as a time-dependent vector potential via the Peierls phase in the Hamiltonian. We find that, in the Bose-Einstein condensation regime where the normal state is semiconducting, the excitonic order is suppressed when the frequency of the pulse light is slightly larger than the band gap, while the order is enhanced when the frequency of the pulse is much larger than the band gap. We moreover find that the excitonic order is completely destroyed in the former situation if the intensity of the pulse is sufficiently strong. In the BCS regime where the normal state is semimetallic, we find that the excitonic order is always suppressed, irrespective of the frequency of the pulse light. The quasiparticle band structure and optical conductivity spectrum after the pumping are also calculated for the instantaneous states.