1/4 is the new 1/2: Interaction-induced topological Mott insulator
Abstract: While the recent advances in topology have led to a classification scheme for electronic bands described by the standard theory of metals, a similar scheme has not emerged for strongly correlated systems such as Mott insulators in which a partially filled band carries no current. By including interactions in the topologically non-trivial spinful Haldane model, we show that a quarter-filled state emerges as a topological Mott insulator with a non-zero Chern number provided the interactions are sufficiently large. We establish this result first analytically by solving exactly a model in which interactions are local in momentum space. We then obtain the same result for the Hubbard interaction by carrying out determinantal quantum Monte-Carlo simulations, lending credence to the claim that both interactions lie in the same universality class. Similar conclusion applies to an interacting quantum spin Hall system. In this case, a topological Mott insulator beyond the standard Z2 topological classification appears at quarter-filling under strong correlation. An intermediate interacting regime that exhibits a quantum anomalous Hall effect emerges when the lower band is `flat', consistent with the observation in the transition metal dichalcogenide moiré materials.
About the QSQM: The EFRC-QSQM center aims to develop and apply nontrivial quantum sensing to measure and correlate local and nonlocal quantum observables in exotic superconductors, topological crystalline insulators, and strange metals. The center is led by the University of Illinois at Urbana-Champaign in partnership with the University of Illinois at Chicago and the SLAC National Accelerator Laboratory.