Graphene, a single layer of carbon atoms in a hexagonal lattice, has already been recognized for its exotic properties that have paved the way for groundbreaking discoveries in the field of physics. However, when two or more layers of graphene are combined, an entirely new realm of possibilities opens up. The recent research conducted by RIKEN physicists sheds light on how magnetic fields can be used to engineer flat bands in twisted graphene layers, creating a playground for even more exotic physics.
When two sheets of graphene with a repeating pattern are placed on top of each other and one sheet is rotated, a moiré pattern emerges, leading to a significant change in properties. At specific twisted angles, the bilayer graphene can exhibit behaviors of a correlated insulator as well as superconductivity. The introduction of twisted angles alters the band structure of graphene, resulting in flat bands where the interactions between electrons become the dominant force, giving rise to various correlated electronic phenomena.
Ching-Kai Chiu and Congcong Le, along with their team at the RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), have demonstrated that twisted bilayer graphene can become an even richer playground for exotic physics when subjected to a spatially varying magnetic field. By introducing a spatially alternating magnetic field, they have identified additional magic angles and flat bands that are quadruply degenerate. This higher degeneracy opens up the possibility for even more correlated phenomena and offers a novel degree of freedom to tailor the electronic band structure.
The discovery of strongly correlated electrons in magic-angle twisted bilayer graphene devices has had a significant impact on the physics community, sparking both shock and excitement. The quadruply degenerate flat bands created by the introduction of a magnetic field have the potential to lead to a new wave of discoveries in the realm of exotic physics. The search is now on to find other materials that exhibit similar phenomena, with the goal of systematically expanding the understanding of flat bands and correlated electronic behaviors.
The research conducted by the RIKEN physicists highlights the transformative impact that magnetic fields can have on twisted graphene layers, unlocking a new dimension of exotic physics. The findings have opened up a wealth of opportunities for further exploration and discovery in the field of condensed matter physics, with the potential for new materials and devices that could revolutionize the way we understand and harness electronic properties.
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