Layer-Polarization-Driven Metal-Insulator Transition in multi-band Graphene Moire' Superlattices

Abstract

Graphene/hBN moir\'e superlattices provide a highly tunable platform for exploring emergent quantum phases in low-dimensional systems. Here, we investigate the moir\'e superlattice formed between hBN and ABA-stacked trilayer graphene (TLG), an inherently multi-band system. We demonstrate that the moir\'e potential is not merely a perturbation but a tool to hybridize the distinct massless and massive electronic sectors of TLG. By applying a perpendicular displacement field to tune layer polarization, we drive a fundamental reconstruction of the electronic band structure. Specifically, increasing the displacement field evolves the system from a multi-band regime to an effectively single-band regime at low energies, accompanied by a metal--insulator transition at the hole-doped secondary Dirac point. This transition originates from a redistribution of carriers across graphene layers that selectively enhances their coupling to the extrinsic moir\'e potential. Quantum capacitance measurements provide direct evidence for the suppression of the density of states at the hole-side secondary Dirac point, consistent with gap opening and the emergence of a displacement-field-tuned band gap. Theoretical calculations reproduce these observations and identify layer-selective coupling to the moir\'e potential as the underlying mechanism. These results demonstrate electrical control of an emergent insulating phase in a low-dimensional moir\'e system, and highlight that layer polarization and layer-selective coupling in multi-band moir\'e heterostructures provide a powerful route for engineering topological and correlated phases through band structure reconstruction and electron interactions.