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Exploring 4D quantum Hall physics with a 2D topological charge pump

机译:使用2D拓扑电荷泵探索4D量子霍尔物理

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摘要

The discovery of topological states of matter has greatly improved our understanding of phase transitions in physical systems. Instead of being described by local order parameters, topological phases are described by global topological invariants and are therefore robust against perturbations. A prominent example is the two-dimensional (2D) integer quantum Hall effect(1): it is characterized by the first Chern number, which manifests in the quantized Hall response that is induced by an external electric field(2). Generalizing the quantum Hall effect to four-dimensional (4D) systems leads to the appearance of an additional quantized Hall response, but one that is nonlinear and described by a 4D topological invariant-the second Chern number(3,4). Here we report the observation of a bulk response with intrinsic 4D topology and demonstrate its quantization by measuring the associated second Chern number. By implementing a 2D topological charge pump using ultracold bosonic atoms in an angled optical superlattice, we realize a dynamical version of the 4D integer quantum Hall effect(5,6). Using a small cloud of atoms as a local probe, we fully characterize the nonlinear response of the system via in situ imaging and site-resolved band mapping. Our findings pave the way to experimentally probing higher-dimensional quantum Hall systems, in which additional strongly correlated topological phases, exotic collective excitations and boundary phenomena such as isolated Weyl fermions are predicted(4).
机译:物质拓扑状态的发现极大地增进了我们对物理系统相变的理解。拓扑阶段不是由局部顺序参数描述,而是由全局拓扑不变量描述,因此对扰动具有鲁棒性。一个著名的例子是二维(2D)整数量子霍尔效应(1):其特征是第一个Chern数,它表现在由外部电场引起的量化霍尔响应中(2)。将量子霍尔效应推广到四维(4D)系统会导致出现额外的量化霍尔响应,但它是非线性的并由4D拓扑不变量-第二Chern数(3,4)描述。在这里,我们报告了具有固有4D拓扑的整体响应的观察结果,并通过测量相关的第二Chern数来证明其量化。通过在成角度的光学超晶格中使用超冷硼原子实现2D拓扑电荷泵,我们实现了4D整数量子霍尔效应的动态版本(5,6)。使用一小部分原子云作为局部探针,我们通过原位成像和位点分辨谱图全面表征了系统的非线性响应。我们的发现为实验探测高维量子霍尔系统铺平了道路,其中预测了其他强相关的拓扑相,奇异的集体激发和边界现象,例如孤立的Weyl费米子(4)。

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  • 来源
    《Nature》 |2018年第7686期|55-58|共4页
  • 作者单位

    Ludwig Maximilians Univ Munchen, Fak Phys, Schellingstr 4, D-80799 Munich, Germany|Max Planck Inst Quantum Opt, Hans Kopfermann Str 1, D-85748 Garching, Germany;

    Ludwig Maximilians Univ Munchen, Fak Phys, Schellingstr 4, D-80799 Munich, Germany|Max Planck Inst Quantum Opt, Hans Kopfermann Str 1, D-85748 Garching, Germany;

    Univ Trento, INO CNR BEC Ctr, Via Sommarive 14, I-38123 Povo, Italy|Univ Trento, Dipartimento Fis, Via Sommarive 14, I-38123 Povo, Italy|Univ Birmingham, Sch Phys & Astron, Birmingham B15 2TT, W Midlands, England;

    ETH, Inst Theoret Phys, Wolfgang Pauli Str 27, CH-8093 Zurich, Switzerland;

    Ludwig Maximilians Univ Munchen, Fak Phys, Schellingstr 4, D-80799 Munich, Germany|Max Planck Inst Quantum Opt, Hans Kopfermann Str 1, D-85748 Garching, Germany;

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  • 正文语种 eng
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  • 入库时间 2022-08-18 02:51:26

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