hBN alignment orientation controls moir\'e strength in rhombohedral graphene

TL;DR

This study demonstrates that the alignment orientation of hBN relative to rhombohedral graphene critically influences moiré potential strength and the resulting correlated phases, revealing a key control parameter for moiré engineering.

Contribution

It uncovers the importance of hBN alignment orientation (0° vs 180°) in determining moiré effects and correlated phases in rhombohedral graphene, supported by experimental and theoretical analysis.

Findings

Different alignment orientations lead to distinct moiré potential strengths.

Experimental contrast in symmetry-broken states based on alignment orientation.

Theoretical model explains the influence of lattice relaxation and atomic structure.

Abstract

Rhombohedral multilayer graphene hosts a rich landscape of correlated symmetry-broken phases, driven by strong interactions from its flat band edges. Aligning to hexagonal boron nitride (hBN) creates a moir\'e pattern, leading to recent observations of exotic ground states such as integer and fractional quantum anomalous Hall effects. Here, we show that the moir\'e effects and resulting correlated phase diagrams are critically influenced by a previously underestimated structural choice: the hBN alignment orientation. This binary parameter distinguishes between configurations where the rhombohedral graphene and hBN lattices are aligned near 0{\deg} or 180{\deg}, a distinction that arises only because both materials break inversion symmetry. Although the two orientations produce the same moir\'e wavelength, we find their distinct local stacking configurations result in markedly different moir\'e potential strengths. Using low-temperature transport and scanning SQUID-on-tip magnetometry, we compare nearly identical devices that differ only in alignment orientation and observe sharply contrasting sequences of symmetry-broken states. Theoretical analysis reveals a simple mechanism based on lattice relaxation and the atomic-scale electronic structure of rhombohedral graphene, supported by detailed modeling. These findings establish hBN alignment orientation as a key control parameter in moir\'e-engineered graphene systems and provide a framework for interpreting both prior and future experiments.