莫尔超晶格场诱导关联绝缘态的量子振荡

Quantum oscillations in field-induced correlated insulators of a moirésuperlattice

本文报道了转角双层-双层石墨烯关联绝缘态中的量子振荡行为.作者发现价带半填充处具有谷各向异性的绝缘态会随着磁场周期性振荡,且最大振幅高达150 kΩ.此外,该绝缘态量子振荡行为可以被垂直方向的电场有效调控.振荡频率随着电场增加线性减小,这表明绝缘态中存在着不断减小的费米面;从振幅变温行为中提取的有效质量随电场变化体现为非线性的行为,但总体保持在0.1me的量级.同样的量子振荡行为也出现在导带半填充处以及非石墨栅极的样品中,表明了该现象的普适性.为了解释该振荡的起源,作者根据实验中提取的与费米面相关的参数构建了反带模型,并通过计算发现能隙中的态密度会随磁场发生振荡,这与实验结果相吻合.本研究表明转角双层-双层石墨烯蕴含着丰富的关联和拓扑现象,是研究凝聚态中的关联物态极好的平台.

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 me 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 moirésystem,our study suggests that TDBG is an excellent platform to discover exotic phases where correlation and topology are at play.