Radiative control of dark excitons at room temperature by nano-optical antenna-tip Purcell effect

Abstract

Excitons, Coulomb-bound electron–hole pairs, are elementary photo-excitations in semiconductors that can couple to light through radiative relaxation. In contrast, dark excitons (XD) show anti-parallel spin configuration with generally forbidden radiative emission. Because of their long lifetimes, these dark excitons are appealing candidates for quantum computing and optoelectronics. However, optical read-out and control of XD states has remained challenging due to their decoupling from light. Here, we present a tip-enhanced nano-optical approach to induce, switch and programmably modulate the XD emission at room temperature. Using a monolayer transition metal dichalcogenide (TMD) WSe2 on a gold substrate, we demonstrate ~6 × 105-fold enhancement in dark exciton photoluminescence quantum yield achieved through coupling of the antenna-tip to the dark exciton out-of-plane optical dipole moment, with a large Purcell factor of ≥2 × 103 of the tip–sample nano-cavity. Our approach provides a facile way to harness excitonic properties in low-dimensional semiconductors offering new strategies for quantum optoelectronics.

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Fig. 1: Schematic of tip-enhanced photoluminescence spectroscopy and electronic band structure of monolayer WSe2.
Fig. 2: Probing radiative emission of dark excitons of monolayer WSe2 through polarization- and power-dependence of tip-enhanced photoluminescence.
Fig. 3: Active control of tip-induced radiative emission of dark excitons of monolayer WSe2.
Fig. 4: Switching and modulation of dark exciton emission.

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Acknowledgements

The authors would like to thank M. D. Lukin for insightful discussions. K.-D.P., T.J. and M.B.R. acknowledge funding from the US Department of Energy, Office of Basic Sciences, Division of Material Sciences and Engineering, under award no. DE-SC0008807. G.C. and X.X. acknowledge support from NSF-EFRI-1433496. We also acknowledge support provided by the Center for Experiments on Quantum Materials (CEQM) of the University of Colorado.

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M.B.R. and K.-D.P. conceived the experiment. K.-D.P. performed the measurements and the FDTD simulations. K.-D.P. and M.B.R. designed the samples, and G.C. and X.X. prepared the samples. K.-D.P. and M.B.R. analysed the data, and all authors discussed the results. K.-D.P. and M.B.R. wrote the manuscript with contributions from all authors. M.B.R. supervised the project.

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Correspondence to Markus B. Raschke.

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Park, K., Jiang, T., Clark, G. et al. Radiative control of dark excitons at room temperature by nano-optical antenna-tip Purcell effect. Nature Nanotech 13, 59–64 (2018). https://doi.org/10.1038/s41565-017-0003-0

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