Tailoring Symmetry Breaking in Engineered van der Waals Superlattices.

Abstract

Superlattice engineering in van der Waals (vdW) heterostructures (e.g., by moiré engineering) provides a powerful platform for designing electronic bands and realizing correlated and topological quantum phenomena. Here, we pioneer a scheme to tailor superpotentials based on intrinsic substrate electronic orders. We show that this establishes a robust, self-aligned, and highly versatile route to band-structure control, as we demonstrate in graphene by engineering two distinct, nearly commensurate superlattices using the charge density waves (CDWs) of 1T-NbSe₂. In these superlattices, the graphene's Dirac cones are folded either to the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>Γ</mi></math> -point or to the K-points of the mini-Brillouin zone (mBZ). Using scanning tunneling microscopy, we observe that the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>Γ</mi></math> -folded system preserves <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>C</mi> <mn>3</mn></msub> </math> symmetry, while the K-folded system exhibits symmetry breaking. Combining density functional theory with an interlayer interaction model, we reveal that this difference is not electronically driven but originates from a structural instability. Our work establishes superlattice engineering for designer quantum states and unveils a structural mechanism for controlled emergent symmetry breaking.