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Published April 12, 2023 | public
Journal Article

Excitonic Beam Steering in an Active van der Waals Metasurface


Two-dimensional transition metal dichalcogenides (2D TMDCs) are promising candidates for ultrathin active nanophotonic elements due to the strong tunable excitonic resonances that dominate their optical response. Here, we demonstrate dynamic beam steering by an active van der Waals metasurface that leverages large complex refractive index tunability near excitonic resonances in monolayer molybdenum diselenide (MoSe₂). Through varying the radiative and nonradiative rates of the excitons, we can dynamically control both the reflection amplitude and phase profiles, resulting in an excitonic phased array metasurface. Our experiments show reflected light steering to angles between −30° and 30° at different resonant wavelengths corresponding to the A exciton and B exciton. This active van der Waals metasurface relies solely on the excitonic resonances of the monolayer MoSe₂ material rather than geometric resonances of patterned nanostructures, suggesting the potential to harness the tunability of excitonic resonances for wavefront shaping in emerging photonic applications.

Additional Information

© 2023 American Chemical Society. The authors gratefully acknowledge support from the Department of Energy-Office of Science under grant DE-FG02-07ER46405. C.U.H. acknowledges support from the Swiss National Science Foundation through the Early Postdoc Mobility Fellowship grant #P2EZP2_191880. We gratefully acknowledge the critical support and infrastructure provided for this work by The Kavli Nanoscience Institute at Caltech. Author Contributions. M.L., C.U.H., and H.A.A. conceived the project. M.L. and C.U.H. fabricated the samples with support from S.B. M.L. and C.U.H. worked on measurements, performed FDTD simulations, and wrote the manuscript. M.L. analyzed the results with assistance from C.U.H. C.U.H. built the experimental setup. H.A.A. supervised the project. All authors discussed the implications of the results and provided important feedback. The authors declare no competing financial interest.

Additional details

August 22, 2023
October 18, 2023