Destabilization of ferromagnetism by frustration and realization of a nonmagnetic Mott transition in the quarter-filled two-orbital Hubbard model

TL;DR

This study uses variational Monte Carlo to explore how frustration affects ferromagnetism and induces a nonmagnetic Mott transition in a quarter-filled two-orbital Hubbard model, revealing suppression of magnetic order with increased frustration.

Contribution

It demonstrates that adding frustration via next-nearest-neighbor hopping suppresses ferromagnetism and enables a nonmagnetic Mott transition in the model.

Findings

Ferromagnetic order is destabilized by frustration.

A nonmagnetic Mott transition occurs with increased frustration.

The variational wave function with doublon-holon binding is more accurate.

Abstract

The two-orbital Hubbard model on a square lattice at quarter filling (electron number per site $n=1$) is investigated by the variational Monte Carlo method. For the variational wave function, we include short-range doublon-holon binding factors. We find that the energy of this wave function is lower than that of the density-density Jastrow wave function partially including long-range correlations used in a previous study. We introduce frustration to the model by the next-nearest-neighbor hopping $t'$ in addition to the nearest-neighbor hopping $t$. For $t'=0$, a ferromagnetic state with staggered orbital order occurs by increasing the Coulomb interaction $U$ before the Mott transition takes place. By increasing $t'$, the region of this ferromagnetic phase shrinks, and the Mott transition without magnetic order occurs.