Moiré patterns have been a subject of fascination in the field of physics for their ability to create new structures with exotic properties. These patterns emerge when two identical or different periodic structures are overlaid, resulting in a pattern of interference fringes. The National University of Singapore (NUS) physicists have now developed a breakthrough technique that allows for precise control of the alignment of supermoiré lattices, opening doors for the advancement of next-generation moiré quantum matter.
Creating a graphene supermoiré lattice poses three main challenges. Firstly, the conventional optical alignment method heavily relies on the straight edges of graphene, making it a time-consuming and labor-intensive process to find suitable graphene flakes. Secondly, even if a straight-edged graphene sample is used, the likelihood of obtaining a double-aligned supermoiré lattice is low due to uncertainties regarding edge chirality and lattice symmetry. Lastly, even when the edge chirality and lattice symmetry are identified, aligning two different lattice materials poses significant physical challenges, often resulting in large alignment errors.
Led by Professor Ariando from the Department of Physics at NUS, a research team devised a technique that addresses these challenges and provides a solution to a real-life problem faced by many researchers. The team successfully achieved the controlled alignment of the hBN (hexagonal boron nitride)/graphene/hBN supermoiré lattice. They also formulated the “Golden Rule of Three” to guide the use of their technique for creating supermoiré lattices. The research findings were published in the prestigious journal Nature Communications.
The researchers developed a set of golden rules to facilitate precise alignment. They employ a 30-degree rotation technique at the beginning to control the alignment of the top hBN and graphene layers. Subsequently, a flip-over technique is used to control the alignment of the top hBN and the bottom hBN layers. These two methods enable the researchers to control the lattice symmetry and adjust the band structure of the graphene supermoiré lattice. Additionally, the team discovered that the neighboring graphite edge can serve as a guide for stacking alignment. With this technique, the researchers successfully fabricated 20 moiré samples with an accuracy better than 0.2 degrees.
The implications of this technique extend beyond moiré quantum matter. The researchers believe their golden rules can benefit scientists working on other strongly correlated systems such as magic-angle twisting bilayer graphene or ABC-stacking multilayer graphene. By offering technical improvements and accelerated fabrication time, these golden rules have the potential to revolutionize the development of the next generation of moiré quantum matter. The applications of this breakthrough extend to the exploration of unique properties in single-layer graphene supermoiré lattices. Furthermore, the team aims to extend this technique to other material systems, unveiling additional novel quantum phenomena.
With the advent of this technique, researchers all over the world can overcome the challenges associated with creating graphene supermoiré lattices. The precise control of the alignment of these lattices opens doors to a vast range of tunable material properties, expanding the applications of moiré patterns. As the research team at NUS continues to unravel the unique properties of moiré quantum matter, the field is poised to witness unprecedented advancements. Although future research will explore the uncharted territory of moiré quantum matter, this breakthrough sets the stage for countless discoveries and innovations in the realm of physics.
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