Current switching of valley polarization in twisted bilayer graphene
Current switching of valley polarization in twisted bilayer graphene
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DOI：
10.1103/physrevb.103.115436
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发表时间：
2021-01
影响因子：
3.7
通讯作者：
Xuzhe Ying;Mengxing Ye;L. Balents
中科院分区：
文献类型：
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作者：
Xuzhe Ying;Mengxing Ye;L. Balents
与六方氮化硼（h-BN）衬底对齐的扭曲双层石墨烯（TBG）可以在3/4填充时表现出异常霍尔效应，这是由于具有相反陈数的谷分辨莫尔带中的自发谷极化[Science 367，900（2020）; Science 365，605（2019）]。据观察，小直流电流能够切换谷极化并反转霍尔电导的符号[Science 367，900（2020）; Science 365，605（2019）]。在这里，我们讨论了在转变温度附近的谷极化的电流开关的机制，其中体耗散输运占主导地位。我们表明，对于旋转对称性破缺的样品，直流电流可能会产生两个谷之间的电子密度差（谷密度差）。电流引起的谷密度差又引起谷极化的一阶转变。我们强调，谷间散射起着核心作用，因为它是两个谷之间交换电子的通道。我们进一步估计谷密度差的TBG/h-BN系统的微观模型，并发现一个显着的增强效果的魔角制度。
Twisted bilayer graphene (TBG) aligned with hexagonal boron nitride (h-BN) substrate can exhibit an anomalous Hall effect at 3/4 filling due to the spontaneous valley polarization in valley resolved moir\'e bands with opposite Chern number [Science 367, 900 (2020); Science 365, 605 (2019)]. It was observed that a small DC current is able to switch the valley polarization and reverse the sign of the Hall conductance [Science 367, 900 (2020); Science 365, 605 (2019)]. Here, we discuss the mechanism of the current switching of valley polarization near the transition temperature, where bulk dissipative transport dominates. We show that for a sample with rotational symmetry breaking, a DC current may generate an electron density difference between the two valleys (valley density difference). The current induced valley density difference in turn induces a first-order transition in the valley polarization. We emphasize that the intervalley scattering plays a central role since it is the channel for exchanging electrons between the two valleys. We further estimate the valley density difference in the TBG/h-BN system with a microscopic model and find a significant enhancement of the effect in the magic angle regime.