Twisted Graphene/CrI Heterostructures Exhibit Tunable Topological States and Anomalous Hall Effects

The interplay between magnetism and topology in two-dimensional materials holds immense promise for future electronic devices, and recent research explores this connection in heterostructures combining graphene and the magnetic insulator chromium triiodide. M. Jafari, M. Gmitra, and A. Dyrdał investigate how twisting these layers together creates unique electronic properties, specifically positioning graphene’s key energy features within the magnetic insulator’s bandgap. This precise alignment, revealed through detailed computational modelling, allows for the manipulation of electron flow and the emergence of novel topological states, potentially transitioning the material between insulating and conducting behaviours. The findings demonstrate a pathway for controlling both magnetism and topology through strain engineering in these van der Waals heterostructures, opening exciting possibilities for spintronic and quantum technologies.

Twisted Graphene and Chromium Triiodide Properties

Researchers have investigated the fascinating interplay of electronic, magnetic, and topological properties in twisted graphene layered on chromium triiodide. They discovered that a specific twist angle dramatically alters the electronic band structure, creating conditions for novel phenomena. This modulation arises from the combined effects of electron exchange and spin-orbit interactions at the interface, opening band gaps and giving rise to topological edge states. Calculations demonstrate that certain twist angles promote the formation of Dirac cones near the Fermi level, which are protected by time-reversal symmetry and exhibit high carrier mobility. Furthermore, the magnetic order of chromium triiodide strongly couples with the spin polarization of graphene, allowing for tunable spin-orbit interaction and control of topological properties with external magnetic fields. This detailed investigation reveals pathways towards designing innovative spintronic devices based on twisted van der Waals heterostructures.

Graphene Twist Controls CrI3 Electronic Interactions

This work presents a comprehensive investigation into the electronic, magnetic, and topological properties of graphene placed on a monolayer of chromium triiodide. Researchers employed first-principles calculations and a mathematical technique to explore how twisting the graphene layer affects their combined behavior. The study identified a specific twist angle that strategically positions graphene’s electronic structure within the energy gap of the chromium triiodide, creating conditions for novel electronic interactions. Scientists then developed a low-energy effective Hamiltonian to accurately model the electronic properties of graphene within this heterostructure, enabling detailed examination of anomalous and valley Hall conductivity.

The team investigated the possibility of a topological phase transition, specifically from a quantum anomalous Hall insulator to a trivial insulating state, and how this transition correlates with changes in the magnetic ground state of the chromium triiodide. Precise computational modeling revealed that the twist angle serves as a critical parameter for tuning the electronic and magnetic characteristics of the combined system, offering potential for controlling topological and magnetic phases within two-dimensional van der Waals heterostructures. The calculations demonstrate strong hybridization of graphene and chromium triiodide orbitals, and how external factors like gate voltage can significantly alter the electronic band structure.
D Materials, Spintronics and Topological States

This extensive list of references details research related to two-dimensional materials, spintronics, topological insulators, and condensed matter physics. The references cover graphene, transition metal dichalcogenides, and other layered materials, focusing on their electronic, optical, and spin-related properties. A central theme is spintronics, with many references dealing with spin transport, spin-orbit coupling, and the spin Hall effect, suggesting research into using electron spin for information processing and storage. References to the Kane-Mele model, Chern insulators, and topological phases indicate research into materials with protected surface states and non-trivial band structures.

Spin-orbit coupling is a recurring theme, crucial for many of the phenomena studied. References also highlight Berry curvature and the anomalous Hall effect, investigating how the geometric properties of the band structure influence transport. The combination of different 2D materials to create novel functionalities is also a key focus.

Graphene-Chromium Triiodide Forms Chern Insulator

This work presents a comprehensive analysis of graphene deposited on a monolayer of chromium triiodide, revealing strong interplay between electronic, magnetic, and topological properties. Researchers identified a specific twist angle between the materials that positions graphene’s electronic structure within the energy gap of the chromium triiodide. They then developed a low-energy model accurately describing the behaviour of electrons in this combined structure, confirming its classification as a Chern insulator exhibiting quantized anomalous Hall conductivity when the chemical potential is within the energy gap. The study also details intrinsic anomalous and valley Hall effects, alongside related Nernst effects, and demonstrates how features in transport measurements can directly determine the bandgap width and splitting in the combined material.

Importantly, the team observed a significant energy difference between the valleys in graphene’s electronic structure, approximately 2 meV, which can be tuned with external gating or a magnetic field, enabling selective control of bandgaps and single-valley transport. The research highlights the potential for strain engineering in these van der Waals heterostructures, demonstrating a pathway to switch quantum anomalous Hall conductivity, potentially encoding logical states for quantum devices. The authors acknowledge that their calculations do not include the effects of substrate materials or encapsulation, representing a direction for future investigation. They also note the substantial Rashba angle present in the system, which influences spin polarization and represents another avenue for further exploration.