Départment de Physique de la Matiére Condensée (DPMC) and Group of Applied Physics (GAP), University of Geneva , 24 Quai Ernest-Ansermet, CH1211 Genéve 4 Switzerland.
Nano Lett. 2014;14(4):2135-9. doi: 10.1021/nl5003922. Epub 2014 Mar 10.
We investigate low-temperature magneto-transport in recently developed, high-quality multiterminal suspended bilayer graphene devices, enabling the independent measurement of the longitudinal and transverse resistance. We observe clear signatures of the fractional quantum Hall effect with different states that are either fully developed, and exhibit a clear plateau in the transverse resistance with a concomitant dip in longitudinal resistance or incipient, and exhibit only a longitudinal resistance minimum. All observed states scale as a function of filling factor ν, as expected. An unprecedented even-denominator fractional state is observed at ν = -1/2 on the hole side, exhibiting a clear plateau in Rxy quantized at the expected value of 2h/e(2) with a precision of ∼0.5%. Many of our observations, together with a recent electronic compressibility measurement performed in graphene bilayers on hexagonal boron-nitride (hBN) substrates, are consistent with a recent theory that accounts for the effect of the degeneracy between the N = 0 and N = 1 Landau levels in the fractional quantum Hall effect and predicts the occurrence of a Moore-Read type ν = -1/2 state. Owing to the experimental flexibility of bilayer graphene, which has a gate-dependent band structure, can be easily accessed by scanning probes, and can be contacted with materials such as superconductors, our findings offer new possibilities to explore the microscopic nature of even-denominator fractional quantum Hall effect.
我们研究了最近开发的高质量多端悬浮双层石墨烯器件中的低温磁输运，这使得能够独立测量纵向和横向电阻。我们观察到具有不同状态的分数量子霍尔效应的清晰特征，这些状态要么完全发展，表现为横向电阻的清晰平台和纵向电阻的相应下降，要么处于初始阶段，仅表现为纵向电阻的最小值。所有观察到的状态都如预期的那样作为填充因子 ν 的函数进行缩放。在空穴侧观察到了一个前所未有的偶数分母分数状态，在 Rxy 中表现出清晰的平台，其量子化值为 2h/e(2)，精度约为 0.5%。我们的许多观察结果，以及最近在六方氮化硼 (hBN) 衬底上的石墨烯双层中进行的电子压缩率测量，与最近的一个理论一致，该理论解释了分数量子霍尔效应中 N = 0 和 N = 1 朗道能级之间简并的影响，并预测了摩尔-里德类型的 ν = -1/2 状态的发生。由于双层石墨烯的实验灵活性，其带结构具有栅极依赖性，可通过扫描探针轻松访问，并且可与超导等材料接触，我们的发现为探索偶数分母分数量子霍尔效应的微观性质提供了新的可能性。
