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Valley Isospin Controlled Fractional Quantum Hall States in Bilayer Graphene
Physical Review X ( IF 12.5 ) Pub Date : 2022-07-28 , DOI: 10.1103/physrevx.12.031019
Ke Huang, Hailong Fu, Danielle Reifsnyder Hickey, Nasim Alem, Xi Lin, Kenji Watanabe, Takashi Taniguchi, Jun Zhu

A two-dimensional electron system placed in a magnetic field develops Landau levels, where strong Coulomb interactions lead to the appearance of many-body correlated ground states. Quantum numbers similar to the electron spin enable the understanding and control of complex ground state order and collective excitations. Owing to its spin, valley, and orbital degrees of freedom, Bernal-stacked bilayer graphene offers a rich platform to pursue correlated phenomena in two dimensions. In this work, we fabricate dual-gated Bernal-stacked bilayer graphene devices and demonstrate unprecedented fine control over its valley isospin degrees of freedom using a perpendicular electric field. Higher sample quality enables us to probe regimes obscured by disorder in previous studies. We present evidence for a new even-denominator fractional quantum Hall state at filling factor ν=5/2. The 5/2 state is found to be spontaneously valley polarized in the limit of vanishing valley Zeeman splitting, consistent with a theoretical prediction made regarding the spin polarization of the Moore-Read state. In the vicinity of the even-denominator fractional quantum Hall states, we observe the appearance of the predicted Levin-Halperin daughter states of the Moore-Read Pfaffian wave function at ν=3/2 and 7/2 and of the anti-Pfaffian at ν=5/2 and 1/2. These observations suggest the breaking of particle-hole symmetry in bilayer graphene. We construct a comprehensive valley polarization phase diagram for the Jain sequence fractional states surrounding filling factor 3/2. These results are well explained by a two-component composite fermion model, further demonstrating the SU(2) nature of the valley isospin in bilayer graphene. Our experiment paves the path for future efforts of manipulating the valley isospin in bilayer graphene to engineer exotic topological orders and quantum information processes.

中文翻译:

双层石墨烯中的 Valley Isospin 控制分数量子霍尔态

放置在磁场中的二维电子系统会产生朗道能级,其中强库仑相互作用导致出现多体相关基态。类似于电子自旋的量子数能够理解和控制复杂的基态顺序和集体激发。由于其自旋、谷和轨道自由度,伯纳尔堆叠双层石墨烯提供了一个丰富的平台来研究二维相关现象。在这项工作中,我们制造了双门控 Bernal 堆叠双层石墨烯器件,并展示了使用垂直电场对其谷同位旋自由度的前所未有的精细控制。更高的样本质量使我们能够探索在以前的研究中被无序掩盖的制度。ν=5/2. 这5/2发现状态在消失谷塞曼分裂的极限内是自发的谷极化,这与关于 Moore-Read 状态的自旋极化的理论预测一致。在偶数分母分数量子霍尔态附近,我们观察到预测的 Moore-Read Pfaffian 波函数的 Levin-Halperin 子态的出现ν=3/27/2和反Pfaffian的ν=5/2-1/2. 这些观察结果表明双层石墨烯中的粒子-孔对称性被破坏。我们为围绕填充因子的 Jain 序列分数态构建了一个综合谷极化相图3/2. 这些结果可以通过双组分复合费米子模型得到很好的解释,进一步证明了双层石墨烯中谷同位旋的 SU(2) 性质。我们的实验为未来操纵双层石墨烯中的谷同位旋以设计奇异的拓扑顺序和量子信息过程铺平了道路。
更新日期:2022-07-29
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