This paper proposes intrinsically stable 2D semiconductor heterostructures with doubly-indirect overlapping bands as optimal platforms for excitonic condensation. Through screening hundreds of 2D materials, the authors identify promising candidate hetero-pairs (Sb₂Te₂Se/BiTeCl, Hf₂N₂I₂/Zr₂N₂Cl₂, and LiAlTe₂/BiTeI) where spontaneous excitonic condensation, mediated by purely electronic interaction, should occur. Unlike previous approaches using monolayers or other bilayers requiring voltage doping, these heterostructures are lattice-matched, exhibit no detrimental electronic instability, and display a broken type-III gap, offering optimal carrier density in true equilibrium. The predicted materials could enable applications in superfluid transport, Josephson-like tunneling, and dissipationless charge counterflow.

Sunny Gupta, Alex Kutana, Boris I. Yakobson