Semiconducting transition metal dichalcogenides (MX2) occur in 2H and rhombohedral (3R) polytypes, respectively distinguished by anti-parallel and parallel orientation of consecutive monolayer lattices. In its bulk form, 3R-MX2 is ferroelectric, hosting an out-of-plane electric polarisation, the direction of which is dictated by stacking. Here, we predict that twin boundaries, separating adjacent polarization domains with reversed built-in electric fields, are able to host two-dimensional electrons and holes with an areal density reaching ∼1013cm−2. Our modelling suggests that n-doped twin boundaries have a more promising binding energy than p-doped ones, whereas hole accumulation is stable at external surfaces of a twinned film. We also propose that assembling pairs of mono-twin films with a `magic' twist angle θ∗ that provides commensurability between the moir\'e pattern at the interface and the accumulated carrier density, should promote a regime of strongly correlated states of electrons, such as Wigner crystals, and we specify the values of θ∗ for homo- and heterostructures of various TMDs.
@article{arxiv.2405.15040,
title = {Two-dimensional electrons at mirror and twistronic twin boundaries in van der Waals ferroelectrics},
author = {James G. McHugh and Xue Li and Isaac Soltero and Vladimir I. Fal'ko},
journal= {arXiv preprint arXiv:2405.15040},
year = {2024}
}