Triplet Exciton-driven Topological Mott insulator at Finite Temperature

Abstract: Motivated by experiments in which the quantum anomalous Hall (QAH) charge gap greatly exceeds the Curie temperature, we apply determinantal quantum Monte Carlo to two complementary lattice models with different geometries: the checkerboard quantum-spin-Hall-Hubbard model and the generalized Kane-Mele-Hubbard model. In both cases an incompressible QAH phase with total Chern number $C=\pm 1$ emerges at quarter filling well above the Curie temperature. Each spin channel carries its own nonquantized Chern number while remaining only partly filled, revealing a topological Mott insulator where Mottness opens the charge gap before magnetic order appears. Charge excitations bind triplet excitons that suppress net magnetization, a many-body dynamical effect absent in mean-field theory. The concurrence of these results on two very different models shows that coupling Mottness with band topology generically yields a high-temperature QAH insulator whose charge excitations are dressed by triplet excitons.