Mott insulating state in a quarter-filled two-orbital Hubbard chain with different bandwidths

TL;DR

This study explores the ground-state properties of a one-dimensional two-orbital Hubbard model with different bandwidths, revealing Mott insulating states at quarter and half fillings and analyzing orbital polarization effects.

Contribution

It introduces a detailed analysis of Mott insulating states in a two-orbital Hubbard chain with bandwidth disparity using DMRG and perturbation theory, highlighting orbital polarization development.

Findings

Charge plateaux indicating Mott insulators at quarter and half fillings.

Orbital polarization develops due to bandwidth differences, influenced by an effective magnetic field.

The Kugel-Khomskii model captures the spin-orbital interactions and orbital pseudo-spin magnetization.

Abstract

We investigate the ground-state properties of the one-dimensional two-band Hubbard model with different bandwidths. The density-matrix renormalization group method is applied to calculate the averaged electron occupancies $n$ as a function of the chemical potential $\mu$. Both at quarter and half fillings, "charge plateaux" appear in the $n$-$\mu$ plot, where $d\mu/dn$ diverges and the Mott insulating states are realized. To see how the orbital polarization in the one-quarter charge plateau develops, we apply the second-order perturbation theory from the strong-coupling limit at quarter filling. The resultant Kugel-Khomskii spin-orbital model includes a $magnetic$ field coupled to orbital pseudo-spins. This field originates from the discrepancy between the two bandwidths and leads to a finite orbital pseudo-spin magnetization.