Abstract:

We report the observation of QΓ intervalley exciton in bilayer WSe2devices encapsulated by boron nitride. The QΓ exciton resides at ∼18 meV below the QK exciton. The QΓ and QK excitons exhibit different Stark shifts under an out-of plane electric field due to their different interlayer dipole moments. By controlling the electric field, we can switch their energy ordering and control which exciton dominates the luminescence of bilayer WSe2. Remarkably, both QΓ and QK excitons exhibit unusually strong two-phonon replicas, which are comparable to or even stronger than the one-phonon replicas. By detailed theoretical simulation, we reveal the existence of numerous (≥14) two-phonon scattering paths involving (nearly) resonant exciton−phonon scattering in bilayer WSe2. To our knowledge, such electric-field-switchable intervalley excitons with strong two-phonon replicas have not been found in any other two-dimensional semiconductors. These make bilayer WSe2 a distinctive valleytronic material with potential novel applications.

Bio:

Mashael M. Altaiary, Ph.D. is an assistant professor in the Department of Physics at University of Jeddah, Jeddah, Saudi Arabia (UJ). She obtained her Ph.D. degree in Physics at University of California, Riverside in 2022; and received her M.S. in 2016. Her research focused on studying the optical properties of 2D materials, including graphene, transition metal dichalcogenides, boron nitride and their heterostructures, by means of frequency- and time-resolved optical spectroscopy. She is also expanding her research towards investigation of ultrafast dynamics in van der Waals heterostructures. She is an expert in fabricating ultraclean 2D heterostructure devices using a state-of-the-art transfer microscope. Dr. Altaiary operated a state-of-the-art ultrafast laser system, built a sophisticated optical pump-probe setup. Her current research interest includes quantum materials, energy stored materials, photonics and optoelectronics, ultrafast spectroscopy.