美国麻省理工学院Yi Yang和Charles Roques-Carmes研究组近日取得一项新成果。经过不懈努力，他们发现了自由电子辐射的光子平带谐振。相关论文于2023年1月4日发表在《自然》杂志上。

研究人员从理论上揭示了光子平带可以克服这种维度失配，从而显著提高光子电子的相互作用。该研究团队在绝缘体上硅光子晶体板中设计了平带谐振，通过调整其轨迹和速度来控制和增强相关的自由电子辐射。

研究人员观察到平带增强的特征，从传统的衍射使史密斯-珀塞尔辐射增加了两个数量级。这种增强使自由电子辐射的偏振整形和通过电子束测量的光子带的表征成为可能。他们的结果支持了平带作为强光-电子相互作用试验平台，特别是与高效和紧凑的自由电子光源和加速器相关。

据了解，平带已经成为当代凝聚态物理学和光子学的基石。在电子学中，平带具有相当的能量带宽和库仑相互作用，导致了相关的现象，如分数量子霍尔效应和最近的魔角系统。在光子学中，它们可以实现包括慢光和激光在内的特性。值得注意的是，平带在两个系统中都支持超准直——无衍射波包传播。不过，平带从未被证明会影响自由电子和光子之间的核心相互作用。它们之间的相互作用对自由电子激光器、显微镜和光谱学以及粒子加速器至关重要，但事实上，它们之间的相互作用受限于局域电子和扩展光子之间的维度失配。

附：英文原文

Title: Photonic flatband resonances for free-electron radiation

Author: Yang, Yi, Roques-Carmes, Charles, Kooi, Steven E., Tang, Haoning, Beroz, Justin, Mazur, Eric, Kaminer, Ido, Joannopoulos, John D., Soljai, Marin

Issue&Volume: 2023-01-04

Abstract: Flatbands have become a cornerstone of contemporary condensed-matter physics and photonics. In electronics, flatbands entail comparable energy bandwidth and Coulomb interaction, leading to correlated phenomena such as the fractional quantum Hall effect and recently those in magic-angle systems. In photonics, they enable properties including slow light1 and lasing2. Notably, flatbands support supercollimation—diffractionless wavepacket propagation—in both systems3,4. Despite these intense parallel efforts, flatbands have never been shown to affect the core interaction between free electrons and photons. Their interaction, pivotal for free-electron lasers5, microscopy and spectroscopy6,7, and particle accelerators8,9, is, in fact, limited by a dimensionality mismatch between localized electrons and extended photons. Here we reveal theoretically that photonic flatbands can overcome this mismatch and thus remarkably boost their interaction. We design flatband resonances in a silicon-on-insulator photonic crystal slab to control and enhance the associated free-electron radiation by tuning their trajectory and velocity. We observe signatures of flatband enhancement, recording a two-order increase from the conventional diffraction-enabled Smith–Purcell radiation. The enhancement enables polarization shaping of free-electron radiation and characterization of photonic bands through electron-beam measurements. Our results support the use of flatbands as test beds for strong light–electron interaction, particularly relevant for efficient and compact free-electron light sources and accelerators.

DOI: 10.1038/s41586-022-05387-5

Source: https://www.nature.com/articles/s41586-022-05387-5