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Creating a custom-designed moiré magnifying glass to probe local atomic lattice rotations in twisted bilayer graphene

Chen-Yue Hao, Jia-Qi He, Huai-Jia Qiao, Yi-Wen Liu, Ya-Ning Ren, and Lin He
Phys. Rev. B 108, 125429 – Published 21 September 2023
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  • INTRODUCTION
  • EXPERIMENT
  • RESULTS AND DISCUSSION
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    Moiré materials have risen to the forefront of physics research because of their ability to realize a disparate set of fascinating physical phenomena in these systems. Besides interesting electronic properties, the moiré pattern has been suggested to be used as a magnifying glass for local strain and dislocations in van der Waals (vdW) systems. Here, we demonstrate the ability to create a custom-designed moiré magnifying glass to probe local atomic lattice rotations directly in tiny-angle twisted bilayer graphene (TBG). In tiny-angle TBG, a moiré periodic network of local subdegree lattice rotations, i.e., the structural reconstruction, occurs due to the vdW interlayer interaction. By introducing a small-period graphene moiré pattern as the magnifying glass, the local subdegree lattice rotations in the underlying tiny-angle TBG are magnified both in structure, i.e., the local moiré periods, and in electronic properties, i.e., energy separations between two low-energy van Hove singularities. Our results unveil the unique magnifying effects of the moiré pattern, and the reported method can be applied to probe the structural reconstruction in any vdW system.

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    • Received 14 July 2023
    • Accepted 13 September 2023

    DOI:https://doi.org/10.1103/PhysRevB.108.125429

    ©2023 American Physical Society

    Physics Subject Headings (PhySH)

    1. Physical Systems
    GrapheneTwisted heterostructures
    1. Techniques
    Scanning tunneling microscopyScanning tunneling spectroscopy
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Chen-Yue Hao, Jia-Qi He, Huai-Jia Qiao, Yi-Wen Liu, Ya-Ning Ren*, and Lin He†

    • Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing 100875, China and Key Laboratory of Multiscale Spin Physics, Ministry of Education, Beijing 100875, China

    • *Corresponding author: yning@mail.bnu.edu.cn
    • †Corresponding author: helin@bnu.edu.cn

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    Vol. 108, Iss. 12 — 15 September 2023

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    Images

    • Figure 1
      Figure 1

      Local lattice rotation of tiny-angle TBG magnified by the topmost moiré. (b)–(d) Schematic pictures showing two structures of a moiré magnifying glass on top of a tiny-angle TBG. One shows that the rotation direction for the first graphene layer is opposite to that of the second layer [(b); and (d), left] and the other is the same as that of the second layer [(c); (d), right]. (d) Schematic of the moiré pattern of the tiny-angle TBG. The green and purple arrows indicate directions of the local lattice rotation of the AA and AB/BA regions, respectively. (a) and (e) Simulated topmost moiré patterns in the AA and AB regions of the underlying tiny-angle TBG for the structures in (b) and (c), respectively.

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    • Figure 2
      Figure 2

      Structure characterization of the moiré magnifying glass on top of two tiny-angle TBG. (a) and (d) Representative STM images of S1 (a) and S2 (d), both showing the “double-moiré” features. The moiré structure in the underlying TBG is marked with circles and lines. The scanning parameters are VBias=−300 mV and I=150 pA. (b) Schematic of the experimental device setup. (c) A representative optical image of the device setup.

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    • Figure 3
      Figure 3

      Effects of the local lattice rotations magnified by the topmost moiré. (a)–(d) Results of S1. (e)–(h) Results of S2. (a) and (e) The spatial-dependent periods of the topmost moiré L12 for the regions in Fig. 2 and 2, respectively. (b) and (f) Spatial distributions of local twist angle θ12 in (a) and (e), respectively. (c) and (g) Maps of ΔEVHS in the topmost moiré, plotted according to 10 000 STS spectra recorded at different positions in each panel. The moiré structure in the underlying TBG is marked with circles and lines. (d) and (h) Left: Representative dI/dV spectra in the AA, AB, and DW regions of the underlying moiré. The dashed curves are the result of Gaussian fitting for each peak. Right: Schematic showing relative positions of the Dirac cones with different twist angles. The red, vertical dotted lines represent the positions of the VHSs.

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    • Figure 4
      Figure 4

      Spatial variation of electronic properties magnified by the topmost moiré. (a)–(d) STS maps of S1 with a fixed sample bias: 130, −128, −60, and 165 mV, respectively. I=250 pA. (e)–(h) STS maps of S2 with a fixed sample bias: −20, −60, −130, and 140 mV, respectively. I=200 pA. The relative positions of the measured energies are shown in the top-right corner of each panel. The moiré structure in the underlying TBG is marked with circles and lines.

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