Anomalous sequence of quantum Hall liquids revealing a tunable Lifshitz transition in bilayer graphene.
Anomalous sequence of quantum Hall liquids revealing a tunable Lifshitz transition in bilayer graphene.
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DOI：
10.1103/physrevlett.113.116602
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发表时间：
2014-03
影响因子：
8.6
通讯作者：
Anastasia Varlet;D. Bischoff;Pauline Simonet;Kenji Watanabe;T. Taniguchi;T. Ihn;K. Ensslin;M. Mucha-Kruczyński;V. Fal’ko
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文献类型：
--
作者：
Anastasia Varlet;D. Bischoff;Pauline Simonet;Kenji Watanabe;T. Taniguchi;T. Ihn;K. Ensslin;M. Mucha-Kruczyński;V. Fal’ko
双层石墨烯是一种可以同时调节费米能量和低能电子色散的独特体系。这是由于三角翘曲和横向电场打开的带隙之间的相互作用而产生的。在这里，我们通过在h-BN封装的双层石墨烯结构上施加一个大的横向电场，将双层石墨烯中的Lifshitz转变驱动到实验上可控的载流子密度。我们进行了磁输运测量，并研究了朗道能级谱中的不同简并现象。在低磁场下，对填充因子为-3和-6的量子霍尔态的观测表明，在价带色散的顶部存在三个极大值。在强磁场下，观察到了所有的整数量子霍尔态，这表明在价带更深的地方，恒定的能量轮廓是单连接的。我们在奇数填充因子下观察到的铁磁量子霍尔态的事实证明了我们的样品的高质量。这使得我们能够识别在中等磁场下关联的量子霍尔态之间的几个相变，这与计算的朗道能级谱的演化一致。因此，观察到的简并演化揭示了我们系统中Lifshitz转变的存在。
Bilayer graphene is a unique system where both the Fermi energy and the low-energy electron dispersion can be tuned. This is brought about by an interplay between trigonal warping and the band gap opened by a transverse electric field. Here, we drive the Lifshitz transition in bilayer graphene to experimentally controllable carrier densities by applying a large transverse electric field to a h-BN-encapsulated bilayer graphene structure. We perform magnetotransport measurements and investigate the different degeneracies in the Landau level spectrum. At low magnetic fields, the observation of filling factors -3 and -6 quantum Hall states reflects the existence of three maxima at the top of the valence-band dispersion. At high magnetic fields, all integer quantum Hall states are observed, indicating that deeper in the valence band the constant energy contours are singly connected. The fact that we observe ferromagnetic quantum Hall states at odd-integer filling factors testifies to the high quality of our sample. This enables us to identify several phase transitions between correlated quantum Hall states at intermediate magnetic fields, in agreement with the calculated evolution of the Landau level spectrum. The observed evolution of the degeneracies, therefore, reveals the presence of a Lifshitz transition in our system.