Topological insulators—materials that are insulating in the bulk but allow electrons to flow on their surface—are striking examples of materials in which topological invariants are manifested in robustness against perturbations such as defects and disorder1. Their most prominent feature is the emergence of edge states at the boundary between areas with different topological properties. The observable physical effect is unidirectional robust transport of these edge states. Topological insulators were originally observed in the integer quantum Hall effect2 (in which conductance is quantized in a strong magnetic field) and subsequently suggested3–5 and observed6 to exist without a magnetic field, by virtue of other effects such as strong spin–orbit interaction. These were systems of correlated electrons. During the past decade, the concepts of topological physics have been introduced into other fields, including microwaves7,8, photonic systems9,10, cold atoms11,12, acoustics13,14 and even mechanics15. Recently, topological insulators were suggested to be possible in exciton-polariton systems16–18 organized as honeycomb (graphene-like) lattices, under the influence of a magnetic field. Exciton-polaritons are part-light, part-matter quasiparticles that emerge from strong coupling of quantum-well excitons and cavity photons19. Accordingly, the predicted topological effects differ from all those demonstrated thus far. Here we demonstrate experimentally an exciton-polariton topological insulator. Our lattice of coupled semiconductor microcavities is excited non-resonantly by a laser, and an applied magnetic field leads to the unidirectional flow of a polariton wavepacket around the edge of the array. This chiral edge mode is populated by a polariton condensation mechanism. We use scanning imaging techniques in real space and Fourier space to measure photoluminescence and thus visualize the mode as it propagates. We demonstrate that the topological edge mode goes around defects, and that its propagation direction can be reversed by inverting the applied magnetic field. Our exciton-polariton topological insulator paves the way for topological phenomena that involve light–matter interaction, amplification and the interaction of exciton-polaritons as a nonlinear many-body system.A part-light, part-matter exciton-polariton topological insulator is created in an array of semiconductor microcavities.

中文翻译：

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激子-极化子拓扑绝缘体

拓扑绝缘体——整体绝缘但允许电子在其表面流动的材料——是突出的例子，其中拓扑不变量表现出对干扰（如缺陷和无序）的鲁棒性1。它们最突出的特点是在具有不同拓扑特性的区域之间的边界处出现边缘状态。可观察到的物理效应是这些边缘状态的单向稳健传输。拓扑绝缘体最初是在整数量子霍尔效应 2（其中电导在强磁场中量化）中观察到的，随后建议 3-5 和观察到 6 在没有磁场的情况下存在，这得益于其他效应，例如强自旋轨道相互作用。这些是相关电子系统。在过去的十年中，拓扑物理学的概念已被引入其他领域，包括微波 7、8、光子系统 9、10、冷原子 11、12、声学 13、14 甚至力学 15。最近，在磁场的影响下，拓扑绝缘体被认为可能在激子极化系统 16-18 中组织为蜂窝（类石墨烯）晶格。激子极化子是部分光、部分物质的准粒子，由量子阱激子和腔光子的强耦合产生。因此，预测的拓扑效应与迄今为止证明的所有拓扑效应不同。在这里，我们通过实验证明了激子极化子拓扑绝缘体。我们的耦合半导体微腔晶格被激光非共振激发，外加磁场导致极化波包围绕阵列边缘单向流动。这种手性边缘模式由极化子凝聚机制构成。我们在真实空间和傅立叶空间中使用扫描成像技术来测量光致发光，从而在模式传播时对其进行可视化。我们证明拓扑边缘模式绕过缺陷，并且可以通过反转施加的磁场来反转其传播方向。我们的激子-极化子拓扑绝缘体为涉及光-物质相互作用、放大和激子-极化子相互作用作为非线性多体系统的拓扑现象铺平了道路。创建了部分光、部分物质激子-极化子拓扑绝缘体在一系列半导体微腔中。这种手性边缘模式由极化子凝聚机制构成。我们在真实空间和傅立叶空间中使用扫描成像技术来测量光致发光，从而在模式传播时对其进行可视化。我们证明拓扑边缘模式绕过缺陷，并且可以通过反转施加的磁场来反转其传播方向。我们的激子-极化子拓扑绝缘体为涉及光-物质相互作用、放大和激子-极化子相互作用作为非线性多体系统的拓扑现象铺平了道路。创建了部分光、部分物质激子-极化子拓扑绝缘体在一系列半导体微腔中。这种手性边缘模式由极化子凝聚机制构成。我们在真实空间和傅立叶空间中使用扫描成像技术来测量光致发光，从而在模式传播时对其进行可视化。我们证明拓扑边缘模式绕过缺陷，并且可以通过反转施加的磁场来反转其传播方向。我们的激子-极化子拓扑绝缘体为涉及光-物质相互作用、放大和激子-极化子相互作用作为非线性多体系统的拓扑现象铺平了道路。创建了部分光、部分物质激子-极化子拓扑绝缘体在一系列半导体微腔中。我们在真实空间和傅立叶空间中使用扫描成像技术来测量光致发光，从而在模式传播时对其进行可视化。我们证明拓扑边缘模式绕过缺陷，并且可以通过反转施加的磁场来反转其传播方向。我们的激子-极化子拓扑绝缘体为涉及光-物质相互作用、放大和激子-极化子相互作用作为非线性多体系统的拓扑现象铺平了道路。创建了部分光、部分物质激子-极化子拓扑绝缘体在一系列半导体微腔中。我们在真实空间和傅立叶空间中使用扫描成像技术来测量光致发光，从而在模式传播时对其进行可视化。我们证明拓扑边缘模式绕过缺陷，并且可以通过反转施加的磁场来反转其传播方向。我们的激子-极化子拓扑绝缘体为涉及光-物质相互作用、放大和激子-极化子相互作用作为非线性多体系统的拓扑现象铺平了道路。创建了部分光、部分物质激子-极化子拓扑绝缘体在一系列半导体微腔中。