- Open Access
Symmetry-based design rules for second-harmonic generation in stacked and twisted bilayers
Phys. Rev. B 114, 225412 – Published 19 October, 2026
DOI: https://doi.org/10.1103/ldws-7yvc
Abstract
Understanding how stacking controls the nonlinear optical response of two-dimensional materials is key to designing van der Waals heterostructures with tailored functionalities. Here, we establish a comprehensive symmetry-based framework mapping the structural configuration of bilayers across four point groups () to their second-order susceptibility tensor . Using group-theory arguments benchmarked against first-principles response-function calculations, we demonstrate how symmetry breaking controls the activation and suppression of individual tensor elements in these systems. We show that the emergence of the in-plane component in twisted configurations ( group) induces a rigid azimuthal rotation of the second-harmonic generation polar lobes, which remains frequency-independent across the entire optical spectrum, locking to half of the structural twist angle. Our findings establish a direct, wavelength-independent optical route for twist-angle determination and provide a clear roadmap for engineering nonlinear optical responses in two-dimensional materials.
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