Breaking Rotational Symmetry in Supertwisted WS<sub>2</sub> Spirals via Moiré Magnification of Intrinsic Heterostrain
Penghong Ci, Yuzhou Zhao, Muhua Sun, Yoonsoo Rho, Yabin Chen, Costas P. Grigoropoulos, Song Jin, Xiaoguang Li, Junqiao Wu
Abstract
Twisted stacking of van der Waals materials with moire uperlattices offers a new way to tailor their physical properties via engineering of the crystal symmetry. Unlike well-studied twisted bilayers, little is known about the overall symmetry and symmetrydriven physical properties of continuously supertwisted multilayer structures. Here, using polarization-resolved second harmonic generation (SHG) microscopy, we report threefold (C 3 ) rotational symmetry breaking in supertwisted WS 2 spirals grown on non-Euclidean surfaces, contrasting the intact symmetry of individual monolayers. This symmetry breaking is attributed to a geometrical magnifying effect in which small relative strain between adjacent twisted layers (heterostrain), verified by Raman spectroscopy and multiphysics simulations, generates significant distortion in the moirepattern. Density-functional theory calculations can explain the C 3 symmetry breaking and unusual SHG response by the interlayer wave function coupling. These findings thus pave the way for further developments in the so-called "3D twistronics".