Tailoring spontaneous symmetry breaking in engineered van der Waals superlattices

TL;DR

This paper introduces a novel superlattice engineering approach in van der Waals heterostructures, using substrate electronic orders to control band structures and induce symmetry breaking in graphene.

Contribution

It demonstrates a new method to tailor superlattices via substrate-induced effects, enabling precise control over electronic and symmetry properties in 2D materials.

Findings

Graphene superlattices engineered with substrate charge density waves show distinct symmetry behaviors.

The difference in symmetry breaking is due to structural instability, not electronic effects.

Superlattice control enables design of quantum states with tailored properties.

Abstract

Superlattice engineering in van der Waals heterostructures (e.\,g.\ by moir\'e engineering) provides a powerful platform for designing electronic bands and realising 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 of 1T-NbSe$_2$. In these superlattices the graphene's Dirac cones are folded either to the $\Gamma$-point or to the K-points of the mini-Brillouin zone. Using scanning tunnelling microscopy, we observe that the $\Gamma$-folded system preserves C$_3$ symmetry, while the K-folded system exhibits spontaneous 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.