Emergent low-energy bound states in the two-orbital Hubbard model

TL;DR

This paper investigates how Coulomb interactions in a two-orbital Hubbard model lead to emergent bound quasiparticle states, revealing a connection between Fermi energy states and inter-band holon-doublon bound states.

Contribution

It introduces an improved dynamical mean field theory approach to study the zero-temperature spectra of the two-orbital Hubbard model, uncovering new bound state phenomena.

Findings

Finite density of states at Fermi energy correlates with bound states at energy gap Δ.

Emergence of inter-band holon-doublon bound states at finite U and U12.

Continuous Mott transition at the symmetric point U=U12.

Abstract

A repulsive Coulomb interaction between electrons in different orbitals in correlated materials can give rise to bound quasiparticle states. We study the non-hybridized two-orbital Hubbard model with intra (inter)-orbital interaction $U$ ($U_{12}$) and different band widths using an improved dynamical mean field theory numerical technique which leads to reliable spectra on the real energy axis directly at zero temperature. We find that a finite density of states at the Fermi energy in one band is correlated with the emergence of well defined quasiparticle states at excited energies $\Delta=U-U_{12}$ in the other band. These excitations are inter-band holon-doublon bound states. At the symmetric point $U=U_{12}$, the quasiparticle peaks are located at the Fermi energy, leading to a simultaneous and continuous Mott transition settling a long-standing controversy.