From flatband to Nagaoka physics: finite-temperature ferromagnetic correlations in the Kagome lattice Hubbard model

Despite being well known for its strong anti-ferromagnetic correlations, under the right conditions, the Fermi-Hubbard model can also exhibit ferromagnetism. Here, we explore the model on the Kagome lattice, which due to the presence of a flatband, is proven to host ferromagnetic long-range order at a certain density range in the ground state. At extreme repulsive interactions, Nagaoka ferromagnetism is also expected to set in close to half filling. Yet, the presence and scope of relevant correlations at finite temperatures has not been systematically explored. 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 experimental simulations of cold fermionic atom in Kagome optical lattices.