A scenario for high-temperature excitonic insulators.

While excitonic insulators (EIs) have been intensively studied, proper platforms of them with stable lattice and non-cryogenic T C are rare. By analysing their Bardeenâ€"Cooperâ€"Schieffer-like gap equation, we propose that high T C EIs can exist in small indirect band gap 2D materials. After screening 2D transition-metal dichalcogenides from existing computational works, we select 2 H -TiTe2 and 1 T -PdTe2, and show that their T C can be as high as 150 to 200 K under strains. A transition of their condensate EI state from that composed by Wannier excitons to that composed by plasmonic ones exists, even if negligible changes are reflected by the EI band structures, demonstrating the rich quantum feature of these systems. The high T C also implies that they are ideal platforms for the demonstration and applications of EIs and their related quantum states in non-cryogenic environments. [ABSTRACT FROM AUTHOR]