Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, has been widely recognized for its exotic properties in the realm of physics. The manipulation of twisted graphene layers has recently emerged as a fascinating area of research, offering a new playground for exploring unconventional physics. RIKEN physicists have delved into the world of twisted bilayer graphene and uncovered how magnetic fields can shape the band structure, paving the way for novel electronic phenomena.
When two or more layers of graphene are stacked on top of each other with a slight rotation, a moiré pattern emerges, leading to a significant change in properties. At specific twist angles, the bilayer graphene exhibits behaviors ranging from correlated insulator to superconductivity. Ching-Kai Chiu and Congcong Le, along with their team at RIKEN iTHEMS, have ventured into this realm and discovered the potential for twisting bilayer graphene further with the introduction of a spatially varying magnetic field.
The band structure of graphene is crucial to its unique electronic properties, characterized by a linear relationship between an electron’s energy and momentum at specific points. By twisting two layers of graphene at certain angles, flat bands can be created where the kinetic energy of electrons is minimized, emphasizing electron-electron interactions. This phenomenon has opened up avenues for exploring correlated electronic behaviors, including unconventional superconductivity.
Chiu and his team have demonstrated that introducing a spatially alternating magnetic field can lead to additional magic angles and flat bands in twisted bilayer graphene. These new bands can exhibit a quadruple degeneracy, offering a higher level of complexity in electronic states. The researchers speculate that this increased degeneracy may give rise to even more correlated phenomena, expanding the possibilities for future exploration in the field of exotic physics.
The discovery of flat bands with enhanced degeneracy in twisted bilayer graphene devices has generated significant interest within the physics community. The magnetic phase introduces a novel degree of freedom to tailor the electronic band structure, opening doors to explore new avenues for engineering exotic physics. The search is now underway to identify other materials that exhibit similar phenomena, with the goal of systematically uncovering new platforms with flat bands and correlated electronic properties.
The study conducted by RIKEN physicists sheds light on the potential of magnetic fields to engineer flat bands in twisted graphene layers, providing an enriched playground for exploring exotic physics. By manipulating the band structure and introducing higher degeneracy, researchers are poised to uncover a wealth of new phenomena in the realm of correlated electronic behaviors. The future holds promise for further advancements in understanding and harnessing the unique properties of twisted bilayer graphene, paving the way for groundbreaking discoveries in the field of condensed matter physics.