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 $\mathit{\text{insulating}}\mathit{\text{charge}}\mathit{\text{ordered}}\mathit{\text{state}}\mathit{\text{with}}\mathit{\text{gapless}}\mathit{\text{excitations}}$and a temperature-driven $\mathit{\text{gapless}}\mathit{\text{topological}}\mathit{\text{insulating}}$ phase. Intrinsic – temperature generated – disorder, is the key ingredient explaining the unexpected behavior. Our findings support the possibility of having temperature-driven topological phase transitions into gapped and gapless topological insulating phases in systems with a large mass unbalance in fermionic species.