Nonequilibrium optical response of a one-dimensional Mott insulator

TL;DR

This paper investigates the nonequilibrium optical properties of a one-dimensional Mott insulator using advanced computational methods, revealing new excitonic phenomena and spectral features after photoexcitation.

Contribution

It introduces a detailed analysis of the nonequilibrium optical response of a 1D Mott insulator, highlighting the emergence of Fano resonances and excitonic states post-pump pulse.

Findings

Identification of mid-gap states related to optical forbidden states

Observation of Fano resonance due to excitonic hybridization

Evidence of excitonic strings, (bi)excitons, and unbound pairs

Abstract

We define, compute and analyze the nonequilibrium differential optical conductivity of the one-dimensional extended Hubbard model at half-filling after applying a pump pulse, using the time-dependent density matrix renormalization group method. The melting of the Mott insulator is accompanied by a suppression of the local magnetic moment and ensuing photogeneration of doublon-holon pairs. The differential optical conductivity reveals $(i)$ mid-gap states related to parity-forbidden optical states, and $(ii)$ strong renormalization and hybridization of the excitonic resonance and the absorption band, yielding a Fano resonance. We offer evidence and interpret such a resonance as a signature of nonequilibrium optical excitations resembling excitonic strings, (bi)excitons, and unbound doublon-holon pairs, depending on the magnitude of the intersite Coulomb repulsion. We discuss our results in the context of pump and probe spectroscopy experiments on organic Mott insulators.