Liu Le, Chu Yanbang, Yang Guang, Yuan Yalong, Wu Fanfan, Ji Yiru, Tian Jinpeng, Yang Rong, Watanabe Kenji, Taniguchi Takashi, Long Gen, Shi Dongxia, Liu Jianpeng, Shen Jie, Lu Li, Yang Wei, Zhang Guangyu
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China.
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China.
Sci Bull (Beijing). 2023 Jun 15;68(11):1127-1133. doi: 10.1016/j.scib.2023.05.006. Epub 2023 May 11.
We report an observation of quantum oscillations (QOs) in the correlated insulators with valley anisotropy of twisted double bilayer graphene (TDBG). The anomalous QOs are best captured in the magneto resistivity oscillations of the insulators at v = -2, with a period of 1/B and an oscillation amplitude as high as 150 kΩ. The QOs can survive up to ∼10 K, and above 12 K, the insulating behaviors are dominant. The QOs of the insulator are strongly D dependent: the carrier density extracted from the 1/B periodicity decreases almost linearly with D from -0.7 to -1.1 V/nm, suggesting a reduced Fermi surface; the effective mass from Lifshitz-Kosevich analysis depends nonlinearly on D, reaching a minimal value of 0.1 m at D = ∼ -1.0 V/nm. Similar observations of QOs are also found at v = 2, as well as in other devices without graphite gate. We interpret the D sensitive QOs of the correlated insulators in the picture of band inversion. By reconstructing an inverted band model with the measured effective mass and Fermi surface, the density of state at the gap, calculated from thermal broadened Landau levels, agrees qualitatively with the observed QOs in the insulators. While more theoretical understandings are needed in the future to fully account for the anomalous QOs in this moiré system, our study suggests that TDBG is an excellent platform to discover exotic phases where correlation and topology are at play.
我们报告了在具有扭曲双层双层石墨烯（TDBG）谷各向异性的关联绝缘体中对量子振荡（QO）的观察结果。异常的QO在绝缘体的磁电阻振荡中表现最为明显，在v = -2时，其周期为1/B，振荡幅度高达150 kΩ。这些QO在高达约10 K的温度下仍能存在，而在12 K以上，绝缘行为占主导。绝缘体的QO强烈依赖于D：从1/B周期性提取的载流子密度随D从-0.7到-1.1 V/nm几乎呈线性下降，这表明费米面减小；通过Lifshitz-Kosevich分析得到的有效质量非线性地依赖于D，在D = ∼ -1.0 V/nm时达到最小值0.1 m。在v = 2时以及在其他没有石墨栅极的器件中也发现了类似的QO观察结果。我们在能带反转的图景中解释了关联绝缘体对D敏感的QO。通过用测量的有效质量和费米面重建一个反转能带模型，由热展宽的朗道能级计算出的能隙处的态密度与绝缘体中观察到的QO在定性上是一致的。虽然未来需要更多的理论理解来全面解释这个莫尔系统中的异常QO，但我们的研究表明TDBG是发现关联和拓扑起作用的奇异相的一个优秀平台。
