The combination of leading hBN, middle graphene and bottom hBn leads to a supermoiré lattice structure at the center of clock. A creative illustration of the supermoiré lattice with twist angles (θt and θb) formed in between graphene and the top layer hexagonal boron nitride (T-hBN) and bottom layer hexagonal boron nitride (B-hBN). The standard optical positioning strongly depends on the straight edges of graphene, but it is time-consuming and labor-intensive to find an appropriate graphene flake; Second, even if the straight-edged graphene sample is utilized, there is a low likelihood of 1/8 to get a double-aligned supermoiré lattice, due to the unpredictability of its edge chirality and lattice symmetry. Third, although the edge chirality and lattice symmetry can be determined, the positioning mistakes are typically discovered to be large (greater than 0.5 degrees), as it is physically challenging to line up 2 various lattice products.
Based on these two methods, they can control the lattice symmetry and tune the band structure of the graphene supermoiré lattice.
The clock design shows the rotation positioning between the hour hand (Top hBN), minute hand (middle graphene) and 2nd hand (Bottom hBN). The mix of top hBN, middle graphene and bottom hBn causes a supermoiré lattice structure at the center of clock. Credit: National University of Singapore
Physicists have established a strategy to precisely align supermoiré lattices, changing the capacity for next-generation moiré quantum matter.
National University of Singapore (NUS) physicists have actually developed a technique to precisely control the positioning of supermoiré lattices by using a set of golden guidelines, paving the method for the improvement of next-generation moiré quantum matter.
Supermoiré Lattices
When two identical periodic structures are overlaid with a relative twist angle in between them or 2 various routine structures however overlaid with or without a twist angle, moiré patterns are formed. The twist angle is the angle between the crystallographic orientations of the two structures. When graphene and hexagonal boron nitride (hBN) which are layered materials are overlaid on each other, the atoms in the 2 structures do not line up perfectly, creating a pattern of interference fringes, called a moiré pattern. This leads to an electronic restoration.
The moiré pattern in graphene and hBN has actually been utilized to create brand-new structures with unique homes, such as topological currents and Hofstadter butterfly states. When 2 moiré patterns are stacked together, a brand-new structure called a supermoiré lattice is developed. Compared to the standard single moiré products, this supermoiré lattice expands the variety of tunable material properties permitting for possible usage in a much bigger range of applications.
Achievements from NUS Physics Department
A research study team led by Professor Ariando from the NUS Department of Physics established a strategy and effectively understood the regulated positioning of the hBN/graphene/hBN supermoiré lattice. This strategy allows for the accurate arrangement of two moiré patterns, one on top of the other. Meanwhile, the researchers also created the “Golden Rule of Three” to assist making use of their technique for creating supermoiré lattices.
The findings were released recently in the journal Nature Communications
An artistic illustration of the supermoiré lattice with twist angles (θt and θb) formed between graphene and the top layer hexagonal boron nitride (T-hBN) and bottom layer hexagonal boron nitride (B-hBN). The minor misalignment causes the development of a supermoiré lattice pattern. Credit: Nature Communications.
Challenges and Solutions
There are 3 main difficulties in developing a graphene supermoiré lattice. Initially, the standard optical alignment strongly depends on the straight edges of graphene, however it is labor-intensive and lengthy to find an ideal graphene flake; Second, even if the straight-edged graphene sample is used, there is a low probability of 1/8 to get a double-aligned supermoiré lattice, due to the unpredictability of its edge chirality and lattice balance. Third, although the edge chirality and lattice balance can be identified, the alignment mistakes are often discovered to be big (greater than 0.5 degrees), as it is physically challenging to line up two various lattice materials.
Dr. Junxiong Hu, the lead author of the research paper, stated, “Our technique assists to fix a real-life issue. Numerous scientists have actually told me that it usually takes practically one week to make a sample. With our method, they can not just greatly reduce the fabrication time, however also considerably enhance the precision of the sample.”
Technical Insights
They use a “flip-over technique” to control the positioning of the top hBN and bottom hBN layers. Based on these two approaches, they can control the lattice proportion and tune the band structure of the graphene supermoiré lattice.
Prof. Ariando said, “We have actually established 3 golden rules for our method which can assist many scientists in the two-dimensional materials neighborhood. Numerous scientists working in other highly associated systems like magic-angle twisting bilayer graphene or ABC-stacking multilayer graphene are likewise anticipated to take advantage of our work. Through this technical improvement, I hope that it will speed up the development of the next generation of moiré quantum matter.”
Future Endeavors
Currently, the research team is leveraging this method to produce the single-layer graphene supermoiré lattice and check out the unique properties of this material system. They are likewise extending the current method to other material systems, to discover other unique quantum phenomena.
Referral: “Controlled positioning of supermoiré lattice in double-aligned graphene heterostructures” by Junxiong Hu, Junyou Tan, Mohammed M. Al Ezzi, Udvas Chattopadhyay, Jian Gou, Yuntian Zheng, Zihao Wang, Jiayu Chen, Reshmi Thottathil, Jiangbo Luo, Kenji Watanabe, Takashi Taniguchi, Andrew Thye Shen Wee, Shaffique Adam and A. Ariando, 12 July 2023, Nature Communications.DOI: 10.1038/ s41467-023-39893-5.