Optical excitations in a one-dimensional Mott insulator

TL;DR

This paper uses advanced numerical methods to analyze optical excitations in a one-dimensional Mott insulator, identifying four distinct types of excitations and their spectral signatures, aligning with theoretical predictions.

Contribution

It provides a detailed numerical investigation of optical excitations in a 1D Mott insulator, revealing four excitation types and their spectral features, validated against theoretical models.

Findings

Four types of optical excitations identified: unbound charge pairs, excitons, excitonic strings, CDW droplets.

Spectral features correspond to different excitations: continuum, peaks, and continua below the Mott gap.

Numerical results agree with field-theoretical and strong-coupling analytical predictions.

Abstract

The density-matrix renormalization-group (DMRG) method is used to investigate optical excitations in the Mott insulating phase of a one-dimensional extended Hubbard model. The linear optical conductivity is calculated using the dynamical DMRG method and the nature of the lowest optically excited states is investigated using a symmetrized DMRG approach. The numerical calculations agree perfectly with field-theoretical predictions for a small Mott gap and analytical results for a large Mott gap obtained with a strong-coupling analysis. Is is shown that four types of optical excitations exist in this Mott insulator: pairs of unbound charge excitations, excitons, excitonic strings, and charge-density-wave (CDW) droplets. Each type of excitations dominates the low-energy optical spectrum in some region of the interaction parameter space and corresponds to distinct spectral features: a continuum starting at the Mott gap (unbound charge excitations), a single peak or several isolated peaks below the Mott gap (excitons and excitonic strings, respectively), and a continuum below the Mott gap (CDW droplets).