Release date: July 24, 2023

News Source& Photographer: Advanced Research Institute of Multidisciplinary Science

Editor: Yang Jing  Auditor: Chen Qi

Translator：Wang Yuhan, News Agency of BIT

As a typical two-dimensional semiconductor material, transition metal dichalcogenides (TMD) have a single-layer atomic thickness of direct bandgap in the near-infrared to visible light bands, which has attracted the attention of many scholars in fields of photonics and optoelectronics.

In momentum space, electrons near the Fermi level will have a new degree of freedom, known as a valley. As is well known, odd layer TMD materials exhibit spatial inversion symmetry breaking and temporal inversion symmetry, resulting in two types of energy valleys K and K '(usually degenerate) that are not equivalent; However, due to spin orbit splitting, , a special light selection rule has emerged in monolayer TMD materials in order to meet the symmetry of time inversion, which can manipulate the valley degree of freedom - valley electronics.

In recent years, quantum emitters (QEs) in two-dimensional semiconductors have attracted great research interest as a promising quantum light source. The single photon emission of quantum emitters (QEs) carrying internal degrees of freedom such as spin and angular momentum plays an important role in quantum optics. However, it is still debated whether these QEs have the same valley physical characteristics as delocalized valley excitons. In addition, the potential applications of this quantum emitter still need to be explored. In view of this, recently, Professor Xu Xiulai from Peking University, Professor Huang Yuan from Beijing Institute of Technology, and Researcher Wang Can from the Institute of Physics, Chinese Academy of Sciences (co corresponding author) collaborated to demonstrate experimental evidence of valley symmetry breaking in monolayer WSe2 quantum emitters through interaction with chiral plasmon nanocavities. The work was published in Nature Communications (titled "Revealing broken valley symmetry of quantum emitters in WSe2 with child nanocavities").

In this work, the anomalous magneto-optical spectra of the coupled QEs indicate that the helicity of the emitted photons remains consistent at two different Zeeman splitting peaks, indicating that the polarization state of the emitted photons is modulated by a chiral nanocavity rather than by valley dependent optical selection rules. The calculation of cavity quantum electrodynamics further proves the lack of intrinsic valley protection characteristics. The cavity-dependent circularly polarized single-photon output also offers a strategy for future applications in chiral quantum optics. Moreover, this work has developed a technique for control of light-matter inter- action at the level of single quanta, indicating potential applications in chiral quantum optics.

The above research work has received support from the National Key R&D Plan, the National Natural Science Foundation of China, and the Beijing Natural Science Foundation.

Paper details and links:

Revealing broken valley symmetry of quantum emitters in WSe2 with chiral nanocavities (Nat. Commun., 2023, DOI:10.1038/s41467-023-39972-7)

Article link: https://www.nature.com/articles/s41467-023-39972-7

Figure 1. Engineering of polarization states of quantum emitter (QE) with broken valley symmetry by chiral plasmonic nanocavities.

Figure 2. Coupling between chiral plasmon resonance and a single quantum emitters.

Figure 3. Circularly polarized resolved magneto-optical spectrum of Qes at chiral plasmon lattice L1 (magnetic field direction perpendicular to the sample surface).

Figure 4. Measured magnetic field-dependent degree of circular polarization (DCP)

Figure 5. Dynamics study and solution of the coupling system between quantum emitters and chiral plasmons.

Attached with the author's introduction:

Huang Yuan is a professor and doctoral supervisor at the Advanced Research Institute of Multidisciplinary Science, BIT. He mainly focused on the preparation, characterization, device processing, and physical property measurement/regulation of two-dimensional materials. In recent years, Huang Yuan and his collaborators have conducted a series of interdisciplinary scientific research in the fields of physics, chemistry, materials, information, and geological sciences. More than 120 SCI papers have been published in Nature Physics, Nature Communications, Physical Review Letters, ACS Nano, Nano Letters etc., where more than 60 articles were published as the first author (including a total of one) and corresponding author. The paper has been cited more than 5700 times. He has led the National Key R&D Program (Youth Project), hosted the National Science and Technology Foundation's Outstanding Youth Fund and General Project, and the Chongqing Outstanding Youth Fund Project. In 2019, he was selected as a member of the Chinese Academy of Sciences Youth Promotion Association. In 2020, he was selected as a member of the Mathematics and Physics Branch of the Chinese Academy of Sciences Youth Promotion Association and was awarded the honorary title of "Top Ten Science and Technology Emerging Figures in China" by the Chinese Association for Science and Technology. In 2021, he was awarded the second prize of the Innovation and Entrepreneurship Award by the Chinese Invention Association (ranked first). In 2022, he was awarded the second prize of the Invention and Entrepreneurship Achievement Award by the Chinese Invention Association (ranked second). In 2023, he received the Silver Award (ranked first) at the Geneva Invention Exhibition. He serves as a reviewer for well-known domestic and international journals such as Physical Review Letters, Nature Communications, ACS Nano, Nano Letters, and Journal of Physics. He also serves as a young editorial board member for journals such as Physics, Chinese Physics Letters, InfoMat, and Materials.