Finite-temperature ferromagnetic correlations in the Kagome lattice Hubbard model: from flatband to Nagaoka physics

Despite being well known for its strong anti-ferromagnetic correlations, under the right conditions, the Fermi-Hubbard model can also host ferromagnetism. Here, we explore the model on the Kagome lattice, which due to the presence of a flatband, is proven to host ferromagnetism at a certain density range in the ground state. At extreme repulsive interactions, Nagaoka ferromagnetism is also expected to set in near half filling. Yet, the extent of correlations at finite temperatures has not been systematically studied. We study short-range spin correlations and other thermodynamic properties using quantum Monte Carlo simulations and the numerical linked-cluster expansions and identify the regions with dominant ferromagnetic correlations as the temperature and interaction strength are varied. Our results can help guide future cold atom experiments in optical lattices.