2023-10-05 米国国立標準技術研究所(NIST)
Illustration depicts two bilayers (two double layers) of graphene that the NIST team employed in their experiments to investigate some of the exotic properties of moiré quantum material . Inset at left provides a top-level view of a portion of the two bilayers, showing the moiré pattern that forms when one bilayer is twisted at a small angle relative to the other.
Credit: B. Hayes/NIST
◆研究では、グラフェン層をねじってモアレ量子物質デバイスを作成し、超低温でエネルギーレベルを調査しました。この新技術は、電子デバイスの設計や微細加工に革命をもたらす可能性があります。また、電気抵抗の新しい基準も提供する可能性があり、工場内でデバイスのキャリブレーションが行えるようになるかもしれません。
＜関連情報＞
- https://www.nist.gov/news-events/news/2023/10/twisted-science-nist-researchers-find-new-quantum-ruler-explore-exotic
- https://www.science.org/doi/10.1126/science.adf2040
モアレ量子物質における軌道磁性のための量子定規 A quantum ruler for orbital magnetism in moiré quantum matter
M. R. Slot,Y. Maximenko,P. M. Haney,S. Kim ,D. T. Walkup,E. Strelcov,Son T. Le,E. M. Shih,D. Yildiz ,S. R. Blankenship,K. Watanabe,T. Taniguchi,Y. Barlas,N. B. Zhitenev,F. Ghahari,and J. A. Stroscio
Science published:5 Oct 2023
Editor’s summary
In a perpendicular magnetic field, electrons in two-dimensional (2D) materials occupy discrete energy levels known as Landau levels. These levels are described by the so-called Onsager relation. Slot et al. used scanning tunneling spectroscopy to measure the Landau levels in twisted double-bilayer graphene with an intermediate twist angle of 1.74° between the two bilayers. By comparing their results against the theoretical expectations, the researchers were able to measure deviations from the standard form of the Onsager relation stemming from the orbital magnetism in the system. —Jelena Stajic
Abstract
For almost a century, magnetic oscillations have been a powerful “quantum ruler” for measuring Fermi surface topology. In this study, we used Landau-level spectroscopy to unravel the energy-resolved valley-contrasting orbital magnetism and large orbital magnetic susceptibility that contribute to the energies of Landau levels of twisted double-bilayer graphene. These orbital magnetism effects led to substantial deviations from the standard Onsager relation, which manifested as a breakdown in scaling of Landau-level orbits. These substantial magnetic responses emerged from the nontrivial quantum geometry of the electronic structure and the large length scale of the moiré lattice potential. Going beyond traditional measurements, Landau-level spectroscopy performed with a scanning tunneling microscope offers a complete quantum ruler that resolves the full energy dependence of orbital magnetic properties in moiré quantum matter.
