Quantum oscillations in correlated insulators of a moiré superlattice

Le Liu, Yanbang Chu, Guang Yang, Yalong Yuan, Fanfan Wu, Yiru Ji, Jinpeng Tian, Rong Yang, Kenji Watanabe, Takashi Taniguchi, Gen Long, Dongxia Shi, Jianpeng Liu, Jie Shen, Li Lu, Wei Yang, Guangyu Zhang

Published 2022-05-20Version 1

Quantum oscillations (QOs) are ubiquitous in metal due to the Landau quantization of cyclotron motion in magnetic field, while they are generally absent in an insulator. Here, we report an observation of QOs in the valley polarized correlated insulators 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 k{\Omega}. The QOs can survive up to ~10K, and above 12K, 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 -1.1V/nm, suggesting a reduced Fermi surface; the effective mass from Lifshitz-Kosevich analysis depends nonlinearly on D, reaching a minimal value of 0.1me at D = ~ -1.0V/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 the inverted bands in a toy model with the measured effective mass and Fermi surface, the density of states calculations of Landau levels agree qualitatively with the observed QOs in the insulators. While more theoretical understandings are needed in the future to fully account for the anomalous quantum oscillations in this moir\'e system, our study suggests that TDBG is an excellent platform to discover exotic phases where correlation and topology are at play.