Abcb-stacked Graphene Exhibits Quantum Anomalous Hall State at Zero Field with Interactions up to 1.0 eV

The pursuit of quantum phenomena in graphene continues to reveal surprising possibilities, and recent work focuses on how interactions between electrons can create novel states of matter. Yulu Ren from Shanghai Jiao Tong University, Yang Shen from ShanghaiTech University, and Chengyang Xu, alongside colleagues including Wanfei Shan from the University of California, Los Angeles, and Weidong Luo from Shanghai Jiao Tong University, demonstrate a pathway to achieving a quantum anomalous Hall state in a specific arrangement of graphene layers. Their research establishes that a unique stacking order, known as ABCB, possesses intrinsic properties that, combined with electron interactions, generates this quantum state without the need for an external electric field, a significant advancement over previous approaches using different graphene arrangements. This discovery highlights the potential of ABCB-stacked graphene as a highly versatile material for exploring and manipulating emergent topological phenomena, paving the way for future advances in quantum technologies.

This material exhibits unusual electronic properties, and the team demonstrates that this topological phase transition arises from the behaviour of electrons within the material itself, rather than requiring an external electric field. Detailed calculations reveal that the combined effect of electron movement and their mutual repulsion opens a topological gap, a key feature for realising the Chern insulator state, and this topological phase remains stable even without an external electric field. The results demonstrate that ABCB-stacked tetralayer graphene provides a promising platform for realising dissipationless edge states, potentially useful in future electronic devices, and offer a new perspective on the role of interactions in topological materials, suggesting that many-body effects can be harnessed to design novel quantum states of matter.

Multilayer Graphene Stacking and Correlated Phenomena

This research focuses on two-dimensional materials, particularly graphene and related multilayer structures, and their complex electronic and correlated phenomena. Researchers are investigating the impact of combining graphene with other two-dimensional materials, such as WSe2 and h-BN, to create heterostructures and study how charge transfer and screening occur between layers, and how spin-orbit coupling can be enhanced. Rhombohedral multilayer graphene, known for its unique electronic properties and potential for correlated phenomena, receives considerable attention, as does ABC-stacked tetralayer graphene due to its potential for ferroelectricity and correlated insulating states. The creation of heterostructures by stacking different two-dimensional materials is a central strategy for engineering novel electronic properties, and advanced computational methods are essential for understanding the complex electronic behaviour of these materials.

Spontaneous Topology in ABCB Tetralayer Materials

This research establishes that ABCB-stacked tetralayer materials can realise a quantum anomalous Hall state without the need for an externally applied electric field, a significant advancement over previous findings. The team demonstrated that the inherent spontaneous polarization within the ABCB structure, combined with strong electron interactions and spin-orbit coupling, is sufficient to drive this topological state. The findings reveal a distinct mechanism for achieving topological states in ABCB stacks compared to ABCA stacks, where an electric field is typically required. The researchers showed how the interplay of spontaneous polarization, electron interactions, and spin-orbit coupling breaks symmetry and induces band inversion, ultimately leading to the quantum anomalous Hall effect, and position ABCB-stacked materials as a highly tunable platform for exploring and potentially harnessing emergent topological phenomena.