Intrinsic layer polarization and multi-flatband transport in non-centrosymmetric mixed-stacked multilayer graphene

TL;DR

This study investigates the electronic properties of ABCBC-stacked pentalayer graphene, revealing intrinsic polarization, tunable band gaps, Lifshitz transitions, and low-field quantum Hall states, highlighting its potential for exploring correlated phenomena.

Contribution

It provides the first detailed analysis of intrinsic layer polarization and multi-flatband transport in non-centrosymmetric mixed-stacked multilayer graphene.

Findings

Observation of an intrinsic band gap at charge neutrality.

Detection of Lifshitz transitions with tuning of displacement field and carrier density.

Emergence of a v = -6 quantum Hall state at very low magnetic field (~20 mT).

Abstract

Graphene multilayers exhibit electronic spectra that depend sensitively on both the number of layers and their stacking order. Beyond trilayer graphene, mixed stacking sequences (alternating Bernal and rhombohedral layers) give rise to multiple coexisting low-energy bands. Here we investigate ABCBC-stacked pentalayer graphene, a less-studied non-centrosymmetric mixed sequence. This stacking can be regarded as an ABC (rhombohedral) trilayer on top of an AB (Bernal) bilayer, so its low-energy band structure contains both a cubic band and a parabolic band that hybridize. In transport measurements, we observe an intrinsic band gap at charge neutrality whose magnitude changes asymmetrically under an applied perpendicular displacement field. This behavior reflects the spontaneous layer polarization inherent to the broken inversion symmetry and mirror symmetry. By tuning the displacement field and carrier density, we drive multiple Lifshitz transitions in the Fermi surface topology and realize Landau levels with different degeneracies arising from the multi-flatband system. Remarkably, a v = -6 quantum Hall state emerges at an exceptionally low magnetic field (~20 mT), indicating the interplay between spontaneous symmetry breaking and Berry curvatures. Our results establish mixed-stacked multilayer graphene as a tunable platform with various broken symmetries and multiple flatbands, suitable for exploring emergent correlated electronic states.