近日，美国宾夕法尼亚州立大学的Mikael C. Rechtsman及其研究团队取得一项新进展。经过不懈努力，他们实现了硅光子晶体中朗道能级的直接观察。相关研究成果已于2024年4月23日在国际知名学术期刊《自然—光子学》上发表。

在这项研究中，研究人员通过实验详细观察了硅光子晶体板中，由应变诱导的伪磁场产生的光子朗道能级。这些朗道能级呈现出色散特性，即它们并非平带，这主要是由于应变导致的晶胞畸变。研究人员尝试采用另一种形式的应变，通过诱导假电位来使能带变得平坦。这种平带类似于空间中的离域空腔，由于光子结构的特性，它们有望显著增强光与物质的相互作用。研究人员在此建立的分析框架能够运用规范场理论，理解光子晶体中非均匀应变的影响，为设计多尺度非周期光子结构提供了有力的指导。

据悉，当电子被限制在二维平面上并受到外部磁场作用时，受到洛伦兹力的影响，它们将在圆形回旋加速器轨道上运动。在量子领域，这种回旋运动呈现量子化特征，因此，电子的能谱会分裂成一系列离散的、高度简并的状态，这些状态被称为朗道能级。这些平带是整数和分数量子霍尔效应产生的根源。尽管光子不受洛伦兹力的影响，因为它们不带电荷，但可以通过周期性断裂应变的方式，使它们产生类似“伪磁场”的效果。

附：英文原文

Title: Direct observation of Landau levels in silicon photonic crystals

Author: Barsukova, Maria, Gris, Fabien, Zhang, Zeyu, Vaidya, Sachin, Guglielmon, Jonathan, Weinstein, Michael I., He, Li, Zhen, Bo, McEntaffer, Randall, Rechtsman, Mikael C.

Issue&Volume: 2024-04-23

Abstract: When electrons are confined to a two-dimensional plane and are subjected to an out-of-plane magnetic field, they move in circular cyclotron orbits as a result of the Lorentz force. In the quantum domain, this cyclotron motion is quantized, and as a consequence, the energy spectrum of the electrons splits into discrete, highly degenerate states called Landau levels. These flat bands are the origin of the integer and fractional quantum Hall effects. Although photons do not experience the Lorentz force because they do not carry charge, they can be made to experience ‘pseudomagnetic fields’ as a result of periodicity-breaking strain. In this work, we experimentally observe photonic Landau levels that arise due to a strain-induced pseudomagnetic field in a silicon photonic crystal slab. The Landau levels are dispersive (that is, they are not flat bands) due to the distortion of the unit cell by the strain. We employ an additional strain of a different form that induces a pseudoelectric potential to flatten them. By acting akin to cavities that are delocalized across space, flat bands such as these have the potential to strongly enhance light–matter interaction as a result of the photonic structure. The analytical framework that we develop here for understanding the effects of inhomogeneous strain in photonic crystals via gauge fields can help to guide the design of multiscale non-periodic photonic structures.

DOI: 10.1038/s41566-024-01425-y

Source: https://www.nature.com/articles/s41566-024-01425-y