Photoinduced enhancement of excitonic order in the two-orbital Hubbard model

TL;DR

This study theoretically investigates how photoexcitation can enhance or suppress excitonic order in a two-orbital Hubbard model, revealing that initial phase regimes determine the outcome of photoinduced dynamics.

Contribution

It demonstrates that photoexcitation can enhance excitonic order in the BEC regime and suppress it in the BCS regime within a two-orbital Hubbard model, highlighting the role of phase dynamics.

Findings

Photoexcitation enhances excitonic order in the BEC regime.

Photoexcitation reduces excitonic order in the BCS regime.

Phase of excitonic pair condensation influences order enhancement.

Abstract

Photoinduced dynamics in an excitonic insulator is studied theoretically by using a two-orbital Hubbard model on the square lattice where the excitonic phase in the ground state is characterized by the BCS-BEC crossover as a function of the interorbital Coulomb interaction. We consider the case where the order has a wave vector $Q=(0,0)$ and photoexcitation is introduced by a dipole transition. Within the mean-field approximation, we show that the excitonic order can be enhanced by the photoexcitation when the system is initially in the BEC regime of the excitonic phase, whereas it is reduced if the system is initially in the BCS regime. The origin of this difference is discussed from behaviors of momentum distribution functions and momentum-dependent excitonic pair condensation. In particular, we show that the phases of the excitonic pair condensation have an important role in determining whether the excitonic order is enhanced or not.