Title:    Electrical Control of Hybrid Excitons in 2D semiconductors

Time:    2025-12-31 10:00

Lecturer:  Shun FENG

École Polytechnique Fédérale de Lausanne (EPFL)

Venue:    Room 2, Energy Materials Building, Xiang'an Campus

Abstract：

In few-layer 2D semiconductors, the spin, valley, energy, and spatial wavefunctions of Coulomb bound electrons and holes can be widely engineered to form the emerging layer-hybridized excitons, towards tailored absorption and emission compared to ‘bare’ exciton counterparts. In the first part, we realized highly tunable excitonic light absorption as function of vertical electric field, in bi- and tri-layer 2H-MoSe2, we observed ground (1s) and excited state (2s) momentum direct (K-K) hybrid dipolar excitons (IX), which exhibit the layer engineered static dipole as well as the exciton g-factor. Moreover, we report the coexisting dipolar and quadrupolar exciton (QX) states in bilayer MoSe2.

Recently we also achieved the electrical switch of quadrupolar/dipolar exciton emission in few layer WSe2 through the band structure cross-over. Furthermore, we proved the general Γ-Λ exciton is a electrical quadrupole which can be layer-engineered. Then, I will present an ambipolar excitonic transistor based on momentum indirect (K-Λ) hybrid IX in bilayer WSe2. We achieved the in-plane field-controlled lateral drag of layer-hybridized trions (charged hybrid excitons). Moreover, we unveil the different transport mobilities of positive and negative trions.

Bio of the Lecturer：

Shun FENG is an awardee of EU Marie Skłodowska-Curie Fellowship and Chinese NSFC Excellent Young Scientist Fund (Overseas). He received his doctorate in Applied Physics from Nanyang Technological University in Singapore (supervisor: Ting YU). After graduation, he worked as a postdoctoral researcher in leading quantum materials optics group (supervisor: Brian Gerardot at Heriot-Watt University, UK) and nanoelectronics group (supervisor: Andras Kis at EPFL, Switzerland). His main research direction is the electrical control of the optical and optoelectronic properties of two-dimensional semiconductors, which provides important insights for the next gen excitonic and photonic devices. In the past few years, his has published his results as the first author in journals such as Physical Review Letters (Editors’ Suggestion), Nature Communication (x2), etc. He received several presentation awards in international conferences, and is a long-term reviewer of Nature Physics, Nature Communication, and Physical Review Letters.