该研究团队报道了由de Haas-van Alphen效应引起的石墨烯热力学磁化振荡的纳米级成像。研究人员利用尖端的超导量子干涉装置（SQUID），在平行于六方氮化硼轴的Bernal双层石墨烯晶体中进行扫描。在弱磁场条件下，他们发现每个电子的磁化振荡幅度达到500玻尔磁振子，频率出乎意料地低，并且对超晶格的填充分数具有高灵敏度。
这些振荡使研究人员能够重建复杂的能带结构，揭示了多个重叠费米面，它们被异常小的动量间隙分隔，形成狭窄的莫尔带。此外，他们还发现了违反教科书中的Onsager-Fermi表面和规则的振荡集，这表明由相干磁击穿引起的宽带粒子-空穴叠加态的形成。
据悉，源自电子回旋轨道量子化的量子振荡提供了对电子带和相互作用的灵敏诊断。
附：英文原文
Title: De Haas–van Alphen spectroscopy and magnetic breakdown in moiré graphene
Author: Matan Bocarsly, Matan Uzan, Indranil Roy, Sameer Grover, Jiewen Xiao, Zhiyu Dong, Mikhail Labendik, Aviram Uri, Martin E. Huber, Yuri Myasoedov, Kenji Watanabe, Takashi Taniguchi, Binghai Yan, Leonid S. Levitov, Eli Zeldov
Issue&Volume: 2024-01-05
Abstract: Quantum oscillations originating from the quantization of electron cyclotron orbits provide sensitive diagnostics of electron bands and interactions. We report on nanoscale imaging of the thermodynamic magnetization oscillations caused by the de Haas–van Alphen effect in moiré graphene. Scanning by means of superconducting quantum interference device (SQUID)–on-tip in Bernal bilayer graphene crystal axis-aligned to hexagonal boron nitride reveals large magnetization oscillations with amplitudes reaching 500 Bohr magneton per electron in weak magnetic fields, unexpectedly low frequencies, and high sensitivity to superlattice filling fraction. The oscillations allow us to reconstruct the complex band structure, revealing narrow moiré bands with multiple overlapping Fermi surfaces separated by unusually small momentum gaps. We identified sets of oscillations that violate the textbook Onsager Fermi surface sum rule, signaling formation of broad-band particle-hole superposition states induced by coherent magnetic breakdown.
DOI: adh3499
Source: https://www.science.org/doi/10.1126/science.adh3499