近日，德国德累斯顿工业大学的Alexey Chernikov与德国离子束物理与材料研究所的Stephan Winnerl等人合作并取得一项新进展。经过不懈努力，他们利用太赫兹光子实现二维材料中三激子的超快开关。相关研究成果已于2024年9月23日在国际知名学生期刊《自然—光子学》上发表。

该研究团队展示了通过在光学注入后施加太赫兹光谱范围内的短脉冲，在单层半导体中实现激子光发射器在超快皮秒时间尺度上的开关。该过程基于通过吸收太赫兹光子诱导光致分离，从而快速将三子转换为激子。

在光学泵浦/太赫兹推动实验中监测时间分辨发射动力学，研究人员实现了所需的共振条件，并展示了该过程随延迟时间和太赫兹脉冲功率的可调性。这项研究结果为复合玻色-费米混合物的发光激发的基础研究引入了一种多功能的实验工具，并为基于原子级薄层材料的新型纳米光子器件的技术开发开辟了道路。

据悉，光学激发的外部控制是操控光-物质耦合的关键，对于光子技术而言极为理想。在此背景下，单层半导体中的激子作为独特的纳米尺度平台脱颖而出，它们提供了强大的光-物质耦合、自旋-谷锁定以及卓越的可调性。

至关重要的是，由于激子发射器与自由电荷载流子之间的高效相互作用，形成了被称为三激子（trions）和费米极化子（Fermi polarons）的新型准粒子，这使得它们的光学响应能够实现电开关。然而，这些状态光发射的调节速度存在重大限制，导致大多数应用基本上局限于静止状态。

附：英文原文

Title: Ultrafast switching of trions in 2D materials by terahertz photons

Author: Venanzi, Tommaso, Cuccu, Marzia, Perea-Causin, Raul, Sun, Xiaoxiao, Brem, Samuel, Erkensten, Daniel, Taniguchi, Takashi, Watanabe, Kenji, Malic, Ermin, Helm, Manfred, Winnerl, Stephan, Chernikov, Alexey

Issue&Volume: 2024-09-23

Abstract: External control of optical excitations is key for manipulating light–matter coupling and is highly desirable for photonic technologies. Excitons in monolayer semiconductors emerged as a unique nanoscale platform in this context, offering strong light–matter coupling, spin–valley locking and exceptional tunability. Crucially, they allow electrical switching of their optical response due to efficient interactions of excitonic emitters with free charge carriers, forming new quasiparticles known as trions and Fermi polarons. However, there are major limitations to how fast the light emission of these states can be tuned, restricting the majority of applications to an essentially static regime. Here we demonstrate switching of excitonic light emitters in monolayer semiconductors on ultrafast picosecond time scales by applying short pulses in the terahertz spectral range following optical injection. The process is based on a rapid conversion of trions to excitons by absorption of terahertz photons inducing photodetachment. Monitoring time-resolved emission dynamics in optical-pump/terahertz-push experiments, we achieve the required resonance conditions as well as demonstrate tunability of the process with delay time and terahertz pulse power. Our results introduce a versatile experimental tool for fundamental research of light-emitting excitations of composite Bose–Fermi mixtures and open up pathways towards technological developments of new types of nanophotonic device based on atomically thin materials.

DOI: 10.1038/s41566-024-01512-0

Source: https://www.nature.com/articles/s41566-024-01512-0