Even-denominator fractional quantum Hall states at an isospin transition in monolayer graphene
Even-denominator fractional quantum Hall states at an isospin transition in monolayer graphene
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DOI：
10.1038/s41567-018-0190-0
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发表时间：
2018-09-01
期刊：
影响因子：
19.6
通讯作者：
Young, A. F.
中科院分区：
文献类型：
--
作者：
Zibrov, A. A.;Spanton, E. M.;Young, A. F.
在单层石墨烯中，两个不等价的碳原子亚晶格与电子自旋结合，赋予电子近四倍简并的内部同位旋。在高磁场下，同位旋简并性增加了二维朗道能级本来就很大的简并性，使低无序石墨烯系统成为研究多组分量子磁性的通用平台。在这里，我们描述了超净单层石墨烯器件的磁电容实验，其中六方氮化硼衬底打破了碳亚晶格之间的对称性。我们观察到同位旋系统中的相变，其特征是填充因子 nu 接近电荷中性时奇数分母分数量子霍尔态发生异常转变，以及在 nu = +/- 1/2 和 nu = +/- 1/4 处意外出现不可压缩偶数分母分数量子霍尔态。我们提出了一种场景，其中观察到的状态是多组分分数量子霍尔态，结合了不同碳亚晶格上电子之间的相关性，与电荷中性时发生的尼尔-价键固体转变的量子霍尔类似物相关。
In monolayer graphene, the two inequivalent sublattices of carbon atoms combine with the electron spin to give electrons a nearly fourfold degenerate internal isospin. At high magnetic fields, the isospin degeneracy increases the already large intrinsic degeneracy of the two-dimensional Landau levels, making low-disorder graphene systems a versatile platform for studying multicomponent quantum magnetism. Here, we describe magnetocapacitance experiments of ultraclean monolayer graphene devices in which a hexagonal boron nitride substrate breaks the symmetry between carbon sublattices. We observe a phase transition in the isospin system, which is marked by unusual transitions in odd-denominator fractional quantum Hall states for filling factors nu near charge neutrality and by the unexpected appearance of incompressible even-denominator fractional quantum Hall states at nu = +/- 1/2 and nu = +/- 1/4. We propose a scenario in which the observed states are multicomponent fractional quantum Hall states incorporating correlations between electrons on different carbon sublattices, associated with a quantum Hall analogue of the Neel-to-valence bond solid transition that occurs at charge neutrality.