Temperature-Driven Gapless Topological Insulator

We investigate the phase diagram of the Haldane-Falicov-Kimball model—a model combining topology, interactions, and spontaneous disorder at finite temperatures. Using an unbiased numerical method, we map out the phase diagram on the interaction-temperature plane. Along with known phases, we unveil an insulating charge ordered state with gapless excitations and a temperature-driven gapless topological insulating phase. Intrinsic—temperature-generated—disorder is the key ingredient explaining the unexpected behavior. Our findings support the possibility of having temperature-driven topological transitions into gapped and gapless topological insulating phases in mass unbalanced systems with two fermionic species.