Effect on electron-hole superfluidity of band flattening from twisting of semiconductor bilayers*

Superfluid condensation of electron-hole pairs has been predicted and subsequently demonstrated to occur at small layer separations in bilayer semiconductor heterostructures [1-2]. The strength of the spatially separated electron-hole pairing is increased when the dispersion of the single electron and hole energy bands is made flatter [3]. It has been shown that twisting two layers of Transition Metal Dichalcogenides or two layers of Black Phosphorus can significantly flatten the single-particle energy bands[4-5]. We systematically calculate realistic multibands of the electrons and holes as a function of twisting angle, so as to follow the change in pairing strength with band flattening. In this way we can investigate the effect of band flattening from twisting on electron-hole superfluid properties.

[1] Pablo López Ríos, et al.  Phys. Rev. Lett. 120, 17701 (2018)

[2] Z. Wang, et al. Nature 574, 76 (2019)

[3] S. Conti, et al. Phys. Rev. B 101, 220504(R) (2020).

[4] Z. Zhang, et al. Nat. Phys. 16, 1093 (2020).

[5] S. Zhao, et al. Nature Communications 12, 3947 (2021)