双层石墨烯中填充因子为 2 的竞争有序态。

Competing ordered states with filling factor two in bilayer graphene.

机构信息

1] Department of Physics and Astronomy, University of California, Riverside, California 92521, USA [2] [3].

1] Department of Physics and Astronomy, University of California, Riverside, California 92521, USA [2].

出版信息

Nat Commun. 2014 Jul 31;5:4550. doi: 10.1038/ncomms5550.

DOI:10.1038/ncomms5550

PMID:25078144

Abstract

The quantum Hall effect, in which a two-dimensional sample's Hall conductivities become quantized, is a remarkable transport anomaly commonly observed at strong magnetic fields. However, it may also appear at zero magnetic field if time-reversal symmetry is broken. Charge-neutral bilayer graphene is unstable to a variety of competing and closely related broken symmetry states, some of which have non-zero quantized Hall conductivities. Here we explore those states by stabilizing them with external fields. Transport spectroscopy measurements reveal two distinct states that have two quantum units of Hall conductivity, stabilized by large magnetic and electric fields, respectively. The majority spins of both phases form a quantum anomalous Hall state, and the minority spins constitute a Kekulé state with spontaneous valley coherence for phase I and a quantum valley Hall state for phase II. Our results shed light on the rich set of competing ordered states in bilayer graphene.

摘要

量子霍尔效应是一种二维样品的霍尔电导率量子化的显著输运异常现象，通常在强磁场中观察到。然而，如果时间反演对称性被破坏，它也可能出现在零磁场中。电荷中性双层石墨烯对各种竞争和密切相关的破对称态不稳定，其中一些具有非零量子霍尔电导率。在这里，我们通过外部场来稳定它们来探索这些状态。输运谱测量显示了两种不同的状态，它们分别由大磁场和电场稳定，具有两个量子霍尔电导率单位。两个相的多数自旋形成量子反常霍尔态，而少数自旋在相 I 中构成具有自发谷相干的凯库勒态，在相 II 中构成量子谷霍尔态。我们的结果揭示了双层石墨烯中丰富的竞争有序态。