In-gap band in the one-dimensional two-orbital Kanamori-Hubbard model with inter-orbital Coulomb interaction

TL;DR

This study uses advanced numerical methods to explore the spectral properties of a one-dimensional two-orbital Kanamori-Hubbard model, revealing in-gap states influenced by inter-orbital interactions and Hund coupling, relevant for understanding multi-orbital materials.

Contribution

It provides a detailed analysis of in-gap states and their origins in the 1D two-orbital Kanamori-Hubbard model, highlighting the effects of inter-orbital Coulomb interaction and Hund coupling.

Findings

In-gap states emerge in the doped system's density of states.

In-gap excitations are mainly inter-orbital holon-doublon states.

Hund interaction broadens the in-gap band.

Abstract

We study the electronic spectral properties at zero temperature of the one-dimensional (1D) version of the degenerate two-orbital Kanamori Hubbard model (KHM), one of the well established frameworks to study transition metal compounds, using state-of-the-art numerical techniques based on the Density Matrix Renormalization Group. While the system is Mott insulating for the half-filled case, as expected for an interacting 1D system, we find interesting and rich structures in the single-particle density of states (DOS) for the hole-doped system. In particular, we find the existence of in-gap states which are pulled down to lower energies from the upper Hubbard band (UHB) with increasing the inter-orbital Coulomb interaction $V$. We analyze the composition of the DOS by projecting it onto different local excitations and we observe that for large dopings these in-gap excitations are formed mainly by inter-orbital holon-doublon (HD) states and their energies follow approximately the HD states in the atomic limit. We observe that the Hund interaction $J$ increases the width of the in-gap band, as expected from the two-particle fluctuations in the Hamiltonian. The observation of a finite density of states within the gap between the Hubbard bands for this extended 1D model indicates that these systems present a rich excitation spectra which could help us understand the microscopic physics behind multi-orbital compounds.