The discovery of correlated insulating states and superconductivity in magic angle twisted bilayer graphene in 2018 has opened up a plethora of new opportunities in the field of condensed matter physics. Researchers found that introducing a tiny twist angle of 1.1 ° between two layers of graphene can form a moiré superlattice, which significantly suppress the kinetic energy of electrons, thereby giving rise to a strongly correlated flatband system. Following the initial discovery, a series of novel quantum phenomena have been discovered in recent years, including orbital magnetism, the quantum anomalous Hall effect, fractional quantum topological states, and unconventional superconductivity.
Recently, Assistant Professor Shuo-Ying Yang from the Southern university of Science and Technology and Professor Cheng Shen from the University of Electronic Science and Technology of China published a review article titled “Twisting Graphene into Correlation and Topology” in National Science Review . Following the main thread of “Twist – Correlation - Topology”, it focuses on the flatband formation mechanism, correlated electronic states, topological quantum states, and unconventional superconducting behavior in magic-angle bilayer graphene, and then further extends the discussion to multilayer twisted graphene systems.
The review highlights that the defining characteristics of magic-angle bilayer graphene is its flatband electronic structure. Because the kinetic energy of electrons is greatly quenched, electronic Coulomb interactions dominate, driving complex electronic behaviors such as correlated insulators, valley-coherent orders, and “heavy-fermion-like” states. Meanwhile, the non-trivial quantum geometry and Berry curvature inherent to the flatband give rise to emergent topological quantum states, such as orbital Chern insulators, quantum anomalous Hall phases, and topological electronic crystals.
Regarding its superconducting properties, a growing body of experimental evidence indicates that superconductivity in twisted graphene deviates from conventional BCS theory, pointing instead toward a strong-coupling, unconventional pairing mechanism.
The enhancement of superfluid stiffness by quantum geometry is also considered as an important factor why superconductivity can remain stable within these flatband systems.
In addition, the review also outlines the development of emerging platforms such as M+N layer graphene, alternating-twist multilayer graphene, and supermoiré systems. Compared with magic-angle bilayer graphene, these configurations exhibit richer band structures, enhanced tunability, and distinct correlated and topological quantum states.
In summary, twisted graphene has transcended its initial conceptualization as a merely rotated two-dimensional material to become a premier platform for investigating strong correlation, topological quantum phases, and unconventional superconductivity. With the continued development of moiré engineering and quantum control technologies, the field of twistronics is expected to further drive the discovery of novel quantum states and their integration into next-generation device applications.
National Science Review