Magnetic properties of the Hubbard model on kagome stripes

TL;DR

This study investigates the magnetic properties of the Hubbard model on kagome chains with flat bands, revealing that ferromagnetism does not persist at finite electron densities in the thermodynamic limit.

Contribution

It provides exact ground state calculations for the Hubbard model on kagome chains, showing the absence of stable ferromagnetism at finite densities.

Findings

Fully polarized ground states exist for certain electron numbers.

No stable ferromagnetism at finite densities in the thermodynamic limit.

Ground states exhibit paramagnetic behavior at large system sizes.

Abstract

We consider the one-orbital $N$-site repulsive Hubbard model on two kagome-like chains, both of which yield a completely dispersionless (flat) one-electron band. Using exact many-electron ground states in the subspaces with $n\le n_{\max}$ ($n_{\max}\propto N$) electrons, we calculate the square of the total spin in the ground state to discuss magnetic properties of the models. We have found that although for $n<n_{\max}$ the ground states contain fully polarized states, there is no finite region of electron densities $n/{\cal{N}} <1$ (${\cal{N}}=N/3$ or ${\cal{N}}=N/5$) where ground-state ferromagnetism survives for ${\cal{N}}\to\infty$.