Speaker
Description
We construct a minimal model of interacting fermions establishing a ferromagnetic insulating phase. It is based on the Hubbard model on a trimerized triangular lattice in the regime of $U\gg t\gg |t^\prime|$ with $t>0$ and $t^\prime$, the intra- and inter-trimer hopping amplitudes respectively. At the $\frac{1}{3}$-filling, each trimer becomes a triplet spin-1 moment, and the inter-trimer superexchange is ferromagnetic with
$J =- \frac{2}{27}\frac{t^{\prime 2}}{t}$ in the limit of $U/t=+\infty$.
As $U/t$ becomes finite, the antiferromagnetic superexchange competes with the ferromagnetic one. The system enters into a frustrated antiferromagnetic insulator when $\lambda>U/t\gg 1$ where $\lambda \sim 10$. In contrast, a similar analysis performed on the trimerized Kagome lattice shows that only antiferromagnetic superchange exits at 1/3-filling. The effect of threading flux is also studied.
