近日，意大利CNR-NANO的Miriam S. Vitiello团队报道了拓扑绝缘子基范德华超材料中二次和三次谐波的产生。该项研究成果发表在2025年9月22日出版的《光：科学与应用》杂志上。

固体中的高次谐波产生（HHG）——光信号的频率上转换——是由对称性控制的。在太赫兹（THz）频率下，HHG是一项关键技术，可以访问传统固态激光技术通常难以覆盖的高频光谱窗口。这种效应最近在石墨烯中得到了利用，HHG在石墨烯中得到了证明，尽管由于其固有的中心对称性，只有驱动频率的奇数倍。在拓扑绝缘体（TIs）中，自旋轨道相互作用和时间反转对称性的结合产生了具有倒带序的绝缘体态，与导电表面态不可分割地联系在一起。据预测，这将支持从体和拓扑表面产生非常规高谐波，这在物理上是难以区分的。然而，到目前为止，还没有实验结果的报道。

研究组利用单或双分裂环谐振器阵列提供的强光场放大，嵌入Bi₂Se₃或(In_xBi_(1-x))₂Se₃/Bi₂Se₃范德华异质结构，在6.4（偶）-9.7（奇）太赫兹频率范围。这是由于体中心对称（奇态）和拓扑表面态（奇偶态）的对称性破缺。

附：英文原文

Title: Second and third harmonic generation in topological insulator-based van der Waals metamaterials

Author: Di Gaspare, Alessandra, Ghayeb Zamharir, Sara, Knox, Craig, Yagmur, Ahmet, Sasaki, Satoshi, Salih, Mohammed, Li, Lianhe, Linfield, Edmund H., Freeman, Joshua, Vitiello, Miriam S.

Issue&Volume: 2025-09-22

Abstract: High-order harmonic generation (HHG) in solids—the frequency up-conversion of an optical signal—is governed by symmetries. At terahertz (THz) frequencies, HHG is a key technology to access high-frequency spectral windows that are usually difficult to cover using conventional solid-state laser technologies. This effect has been recently exploited in graphene, where HHG has been demonstrated, albeit only at odd multiples of the driving frequency owing to its inherent centro-symmetry. In topological insulators (TIs), the combination of spin–orbit interaction and time-reversal symmetry create an insulating bulk state with an inverted band order, inseparably connected with conducting surface states. TIs have been predicted to support unconventional high harmonic generation from the bulk and topological surface, which are usually difficult to distinguish. However, no experimental results have been reported, so far. Here, we exploit the strong optical field amplification provided by an array of single or double split ring resonators, with embedded Bi2Se3 or (InxBi(1x))2Se3/Bi2Se3 Van der Waals heterostructures, to achieve up-conversion in the 6.4 (even)–9.7 (odd)THz frequency range. This results from bulk centro-symmetry (odd states) and symmetry breaking in the topological surface states (odd and even).

DOI: 10.1038/s41377-025-01847-5

Source: https://www.nature.com/articles/s41377-025-01847-5