Time-dependent spectral properties of photoexcited one-dimensional ionic Hubbard model: an exact diagonalization study

TL;DR

This study uses exact diagonalization to analyze how optical excitation affects the spectral and transport properties of a one-dimensional ionic Hubbard model, revealing distinct behaviors in Mott and band insulators.

Contribution

It provides a detailed numerical analysis of time-dependent spectral functions and conductivity in the ionic Hubbard model under optical excitation, highlighting differences between insulator types.

Findings

In-gap density of states correlates with Drude weight and energy absorption.

In a Mott insulator, the Drude peak oscillates at pump frequency and second harmonic.

In a band insulator, the Drude peak oscillates only at pump frequency.

Abstract

Motivated by the recent progress in time-resolved nonequilibrium spectroscopy in condensed matter, we study an optically excited one-dimensional ionic Hubbard model by exact diagonalization. The model is relevant to organic crystals, transition metal oxides, or ultracold atoms in optical lattices. We implement numerical pump-probe measurements to calculate time-dependent conductivity and single-particle spectral functions. In general, short optical excitation induces a metallic behavior imprinted as a Drude peak in conductivity or an in-gap density of states. In a Mott insulator, we find that the induced Drude peak oscillates at the pump frequency and its second harmonic. The former comes from the oscillation of currents, and the latter from the interference of single- and three-photon excited states. In a band insulator, the Drude peak oscillates only at the pump frequency, and quantities such as the double occupancy do not oscillate. The absence of the second harmonic oscillation is due to the degeneracy of multi-photon excited states. The in-gap density of states in both insulators correlates with the Drude weight and the energy absorption for weak pumping. Strong pumping leads to saturation of the in-gap density of states and to suppression of the Drude weight in the Mott regime. We have also checked that the above features are robust for insulators in the intermediate parameter range. Our study demonstrates the distinct natures of the multi-photon excited states in two different insulators.