Optical cavities play crucial roles in enhanced light–matter interaction, light control, and optical communications, but their dimensions are limited by the material property and operating wavelength. Ultrathin planar cavities are urgently in demand for large-area and integrated optical devices. However, extremely reducing the planar cavity dimension is a critical challenge, especially at telecommunication wavelengths. Herein, we demonstrate a type of ultrathin cavities based on large-area grown Bi₂Te₃ topological insulator (TI) nanofilms, which present distinct optical resonance in the near-infrared region. The result shows that the Bi₂Te₃ TI material presents ultrahigh refractive indices of >6 at telecommunication wavelengths. The cavity thickness can approach 1/20 of the resonance wavelength, superior to those of planar cavities based on conventional Si and Ge high refractive index materials. Moreover, we observed an analog of the electromagnetically induced transparency (EIT) effect at telecommunication wavelengths by depositing the cavity on a photonic crystal. The EIT-like behavior is derived from the destructive interference coupling between the nanocavity resonance and Tamm plasmons. The spectral response depends on the nanocavity thickness, whose adjustment enables the generation of obvious Fano resonance. The experiments agree well with the simulations. This work will open a new door for ultrathin cavities and applications of TI materials in light control and devices.

二维材料中的新量子态对凝聚态物理和现代光电器件的发展具有重要意义。然而具有宽带、室温和快速响应能力的太赫兹光电探测技术，由于缺乏暗电流和光吸收之间的最佳平衡，仍然面临着巨大的挑战。在这项研究中，作者合成了新型拓扑绝缘体材料GeBi₄Te₇，并搭建了其与Bi₂Te₃的范德华异质结，以实现高灵敏度的太赫兹光电探测器。在平面金属-材料-金属结构中实现了在室温下将低光子能量太赫兹波段直接转化为光电流。结果表明，基于Bi₂Te₃-GeBi₄Te₇的太赫兹光电探测器能够实现0.02 ~0.54 THz的宽谱探测，且具有很高的光响应率（在 0.112、0.27、0.5 THz下分别为 592 V?W^-1、203 V?W^-1、40 V?W^-1），响应时间小于6 μs。值得注意的是，它被用于高频太赫兹的成像应用演示。这些结果为Bi₂Te₃-GeBi₄Te₇拓扑绝缘体异质结材料的低能量光电应用开辟了可行性途径。

Manipulating motion of microobjects with light is indispensable in various technologies. On solid interfaces, its realizations, however, are hampered by surface friction. To resolve this difficulty, light-induced elastic waves have been recently proposed to drive microobjects against friction. Despite its expected applicability for arbitrary optical-absorptive objects, the new principle has only been tested with microsized gold plates. Herein, we validate this principle using a new material and report directional and continuous movements of a two-dimensional topological insulator (Sb₂Te₃) plate on an untreated microfiber surface driven by nanosecond laser pulses. The motion performance of the Sb₂Te₃ plate is characterized by a scanning electron microscope. We observe that the motion velocity can be controlled by tuning the average power of laser pulses. Further, by intentionally increasing the pulse repetition rate and exploiting the low thermal conductivity of Sb₂Te₃, we examine the thermal effects on actuation and reveal the motion instability induced by formations of microbumps on Sb₂Te₃ surfaces due to the Marangoni effects. Moreover, as the formed microbumps are heated to viscoelasticity states, liquid-like motion featuring asymmetry in contact angles is observed and characterized, which expands the scope of light-induced actuation of microobjects.

在过去的十年里，材料的拓扑相变以及它们的奇异物理现象在固态电子学领域掀起了研究热潮。近些年来，人们开始在其他系统中重现和模拟电子体系中的各种拓扑现象，包括冷原子气体、离子阱、光子学、声子学、机械波和电路体系。在这些体系平台中，由电感电容所组成的拓扑电路因具有高度灵活的设计自由度、高性价比、易加工和易集成的独特优势而备受关注。除此之外，在拓扑电路中可以方便地设计具有任意长程耦合、非线性、非互易、增益等效应的拓扑模型，从而实现很多在电子体系和光学体系中难以实现的非线性、非阿贝尔和非厄米的拓扑相变材料。本文作为拓扑电路领域的第一篇综述，系统性地回顾了过去六年拓扑电路领域的主要进展，重点关注其理论建模、电路设计与实验测量，并对拓扑电路与电子和光学体系中的拓扑绝缘体着重进行讨论和区别。本综述涵盖了多种不同类型的拓扑电路，包括含有非平庸边界态、高阶拓扑角模式以及外尔粒子的厄米拓扑电路，拥有拓扑节线和节点态的高维拓扑电路，具有趋肤效应和由增益/衰减导致的非厄米拓扑电路，自感应拓扑边界态的非线性拓扑电路，以及具有非阿贝尔规范场效应的拓扑电路。