The “Golden Rules” for constructing atomic masses

The clock model shows rotational alignment between the hour hand (top hBN), minute hand (middle graphene), and seconds hand (bottom hBN). The combination of the upper hBN, middle graphene and lower hBn results in a moiré superlattice structure at the center of the watch. Credit: National University of Singapore

Physicists have developed a technique to precisely align super-wavy lattices, revolutionizing the possibility of the next generation of wavy quantum matter.

Physicists at the National University of Singapore (NUS) have developed a technique for precisely controlling the alignment of super-wavering lattices using a set of golden rules, paving the way for the next generation of wavy quantum matter to advance.

Supermoiré lattices

Moiré patterns form when two identical periodic structures are superimposed with a relative torsional angle between them or two different periodic structures but superimposed with or without a torsional angle. Torsion angle is the angle between the crystal orientations of the two structures. For example, when graphene Hexagonal boron nitride (hBN) are materials with layers superimposed on top of each other, and the atoms in the two structures are not lined up perfectly, which creates a pattern of interference fringes, called a moiré pattern. This leads to electronic reconstruction.

The moiré pattern in graphene and hBN has been used to create new structures with exotic properties, such as topological currents and Hofstadter butterfly states. When two moiré patterns are stacked together, a new structure called a moire network is created. Compared to traditional single wave materials, this ultra-wave web extends the range of tunable material properties allowing for potential use in a much wider range of applications.

Achievements of the Department of Physics at NUS University

A research team led by Professor Arriando of the Department of Physics at the National University of Singapore developed a technique and successfully achieved the controlled alignment of the hBN/graphene/hBN supermoiré. This technique allows for the precise arrangement of two moiré patterns, one on top of the other. Meanwhile, the researchers also formulated the “Golden Rule of Three” to guide the use of their technology to create super-ripple networks.

The results were recently published in the journal Nature Communications.

Artist’s illustration of the super-moffered lattice with twisted angles (θt and θb) formed between graphene, the top layer of hexagonal boron nitride (T-hBN) and the bottom layer of hexagonal boron nitride (B-hBN). A slight misalignment leads to the formation of a super-moppy lattice pattern. Credit: Nature Communications

Challenges and solutions

There are three main challenges in creating an ultra-moppy graphene lattice. First, conventional optical alignment relies heavily on straight edges of graphene, but finding a suitable graphene wafer is time-consuming and labor-intensive; Second, even if the straight-edged graphene sample is used, there is a low probability of 1/8 of obtaining a double-aligned moiré lattice, due to uncertainties about edge asymmetry and lattice symmetry. Third, although edge symmetry and lattice symmetry can be determined, alignment errors are often large (greater than 0.5°), since it is physically difficult to align two different lattice materials.

Dr Junxiong Ho, lead author of the research paper, said: “Our technology helps solve a real-life problem. Several researchers told me that it usually takes about a week to process the sample. With our technology, they can not only greatly shorten the manufacturing time, but also greatly improve the performance Accuracy of the sample.”

artistic visions

The scientists are using the “30-degree rotation technique” initially to control the alignment of the hBN top layers and graphene. Then they use an ‘inversion technique’ to control the alignment of the upper hBN layers and the lower hBN layers. Based on these two methods, they can control the lattice symmetry and adjust the band structure of the graphene super-wavelength lattice. They also showed that the adjacent graphite edge can serve as a guide for the stacking alignment. In this study, they synthesized 20 moiré samples with an accuracy of better than 0.2°.

Professor Arriando said: “We have established three golden rules for our technology which can help many researchers in the two-dimensional materials community. Our work is also expected to benefit many scientists working on other strongly correlated systems such as magic angle twisted bilayer graphene or ABC stacked multilayer graphene. Through this technical improvement, I hope it will accelerate the development of the next generation of quantum wave matter.

future endeavors

Currently, the research team is taking advantage of this technology to fabricate a single-layer ultra-wavelength graphene lattice and explore the unique properties of this material system. Moreover, they are also extending the existing technology to other physical systems, to discover other new quantum phenomena.

Reference: “Controlled alignment of the lattice of superlattices in double-aligned graphene heterostructures” by Junxiong Hu, Junyou Tan, Mohamad M. Al Ezzi, Udvas Chattopadhyay, Jian Gou, Yuntian Zheng, Zihao Wang, Jiayu Chen, Reshmi Thottathil, Jiangbo Luo Kenji Watanabe, Takashi Taniguchi, Andrew Tae-Shin Wei, Shafik Adam and A. Arriando, July 12, 2023, Available Here. Nature Communications.
doi: 10.1038/s41467-023-39893-5