近日，美国马里兰大学的You Zhou及其研究团队取得一项新进展。经过不懈努力，他们观察到原子薄半导体中费米极化子的巨大光学非线性。相关研究成果已于2024年5月14日在国际知名学术期刊《自然—光子学》上发表。
该研究团队利用原子薄半导体中激子和载流子之间的耦合，实验证明了具有大振荡强度的强非线性光学响应。通过控制三层WSe2的电场和静电掺杂，研究人员观察到层内和层间激子的杂化和费米极化子的形成。他们在连续波和脉冲激光激发下观察到大量的光学非线性，其中费米极化子共振蓝移高达近10meV。
有趣的是，他们观察到电子和空穴掺杂之间的光学非线性存在显著的不对称性，这种不对称性可以通过外加电场调节。他们将这些特征归因于激子与自由电荷之间的相互作用引起的光诱导谷极化。这项研究结果确立了原子薄异质结构，作为高度通用工程非线性光学响应平台的地位，对于经典和量子光电子学领域具有深远的应用前景。
据悉，实现强非线性光学响应是一个长期的目标，具有重要的基础和技术意义。最近，大量的工作集中在探索固体中的激子，以实现非线性甚至低到几个光子水平。然而，由于强光-物质相互作用需要大的振荡器强度和短的激子辐射寿命，这限制了它们的非线性，因此出现了一个关键的权衡。
附：英文原文
Title: Giant optical nonlinearity of Fermi polarons in atomically thin semiconductors
Author: Gu, Liuxin, Zhang, Lifu, Ni, Ruihao, Xie, Ming, Wild, Dominik S., Park, Suji, Jang, Houk, Taniguchi, Takashi, Watanabe, Kenji, Hafezi, Mohammad, Zhou, You
Issue&Volume: 2024-05-14
Abstract: Realizing strong nonlinear optical responses is a long-standing goal of both fundamental and technological importance. Recently, substantial efforts have been focused on exploring excitons in solids to achieve nonlinearities even down to few-photon levels. However, a crucial tradeoff arises as strong light–matter interactions require large oscillator strength and short radiative lifetime of excitons, which limits their nonlinearity. Here we experimentally demonstrate strong nonlinear optical responses with large oscillator strength by exploiting the coupling between excitons and carriers in an atomically thin semiconductor. By controlling the electric field and electrostatic doping of trilayer WSe2, we observe the hybridization between intralayer and interlayer excitons and the formation of Fermi polarons. Substantial optical nonlinearity is observed under continuous-wave and pulsed laser excitation, where the Fermi polaron resonance blueshifts by as much as ~10meV. Intriguingly, we observe a remarkable asymmetry in the optical nonlinearity between electron and hole doping, which is tunable by the applied electric field. We attribute these features to the optically induced valley polarization due to the interactions between excitons and free charges. Our results establish atomically thin heterostructures as a highly versatile platform for engineering nonlinear optical response with applications to classical and quantum optoelectronics.
DOI: 10.1038/s41566-024-01434-x
Source: https://www.nature.com/articles/s41566-024-01434-x