近日，浙江大学的林晓及其研究小组与以色列理工学院的Ido Kaminer以及新加坡南洋理工大学的张柏乐等人合作，并取得一项新进展。经过不懈努力，他们实现超低能电子的界面切伦科夫辐射
据悉，切伦科夫辐射只有在带电粒子以超过该物质中光的相速度运动时才会发生。这种辐射机制可以在宽频率范围内产生定向光发射，除了难以满足高能粒子的要求外，还可以促进片上光源的发展。然而，利用与自由空间中的光没有动量不匹配的低能电子产生切伦科夫辐射仍然是一个长期存在的挑战。
该研究团队报道了一种克服这一挑战的机制，通过利用界面切伦科夫辐射和umklapp散射的联合效应，即来自序列粒子界面相互作用的光发射与特殊设计的umklapp动量位移的相长干涉。研究发现，这种综合效应能够产生超低能电子的界面切伦科夫辐射，其动能低至电子伏特尺度。由于受激高动量布洛赫模式的umklapp散射，得到的切伦科夫界面辐射具有波锥和群锥空间分离的独特特征。
附：英文原文
Title: Interfacial Cherenkov radiation from ultralow-energy electrons
Author: Gong, Zheng, Chen, Jialin, Chen, Ruoxi, Zhu, Xingjian, Wang, Chan, Zhang, Xinyan, Hu, Hao, Yang, Yi, Zhang, Baile, Chen, Hongsheng, Kaminer, Ido, Lin, Xiao
Issue&Volume: 2023-9-11
Abstract: Cherenkov radiation occurs only when a charged particle moves with a velocity exceeding the phase velocity of light in that matter. This radiation mechanism creates directional light emission at a wide range of frequencies and could facilitate the development of on-chip light sources except for the hard-to-satisfy requirement for high-energy particles. Creating Cherenkov radiation from low-energy electrons that has no momentum mismatch with light in free space is still a long-standing challenge. Here, we report a mechanism to overcome this challenge by exploiting a combined effect of interfacial Cherenkov radiation and umklapp scattering, namely the constructive interference of light emission from sequential particle–interface interactions with specially designed (umklapp) momentum-shifts. We find that this combined effect is able to create the interfacial Cherenkov radiation from ultralow-energy electrons, with kinetic energies down to the electron-volt scale. Due to the umklapp scattering for the excited high-momentum Bloch modes, the resulting interfacial Cherenkov radiation is uniquely featured with spatially separated apexes for its wave cone and group cone.
DOI: 10.1073/pnas.2306601120
Source: https://www.pnas.org/doi/10.1073/pnas.2306601120