Title: Rich electronic phase diagram in kagome flat band

Speaker: Yu-Ping Lin

Affiliation: Department of Physics, University of California, Berkeley

Abstract: The past decade has seen enormous success in the fabrication and characterization of flat-band materials. Among various flat-band systems, there is one family where the flat bands are inherent in the lattice due to frustrated hoppings. In this talk, I show that the kagome lattice, a member of this family, offers a fertile ground for novel correlated phases in the flat band. With the Hartree-Fock approximation, I present the rich mean-field phase diagram of repulsive Hubbard model across all flat band filling. In addition to the flat-band ferromagnetism, our analysis yields cascades of unconventional magnetic orders as filling changes. These include a series of antiferromagnetic (AFM) spin-charge stripe orders, as well as an evolution from 120-degree AFM to intriguing noncoplanar spin orders with tetrahedral structures. The extended repulsion can drive other interesting phases, such as the quantum anomalous Hall ferromagnetism. I further compare our phase diagrams with recent experiments on FeSn and FeGe, which hints at the search for novel magnetic orders in the kagome flat-band materials. Possibilities beyond mean-field theory is also discussed.

Reference: Yu-Ping Lin, Chunxiao Liu, and Joel E. Moore, arXiv:2307.11810