Letter | Published:

Resonant internal quantum transitions and femtosecond radiative decay of excitons in monolayer WSe2

Nature Materials volume 14, pages 889893 (2015) | Download Citation

Abstract

Atomically thin two-dimensional crystals have revolutionized materials science1,2,3. In particular, monolayer transition metal dichalcogenides promise novel optoelectronic applications, owing to their direct energy gaps in the optical range4,5,6,7,8,9. Their electronic and optical properties are dominated by Coulomb-bound electron–hole pairs called excitons10,11,12,13,14,15,16,17,18, whose unusual internal structure13, symmetry15,16,17, many-body effects18 and dynamics have been vividly discussed. Here we report the first direct experimental access to all 1s A excitons, regardless of momentum—inside and outside the radiative cone—in single-layer WSe2. Phase-locked mid-infrared pulses reveal the internal orbital 1s–2p resonance, which is highly sensitive to the shape of the excitonic envelope functions and provides accurate transition energies, oscillator strengths, densities and linewidths. Remarkably, the observed decay dynamics indicates an ultrafast radiative annihilation of small-momentum excitons within 150 fs, whereas Auger recombination prevails for optically dark states. The results provide a comprehensive view of excitons and introduce a new degree of freedom for quantum control, optoelectronics and valleytronics of dichalcogenide monolayers19,20,21,22,23,24.

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Acknowledgements

We thank M. Eisele, T. Cocker, M. Huber, J. Fabian, A. Chernikov, S. Michaelis de Vasconcellos, R. Schmidt and C. Frankerl for helpful discussions and M. Furthmeier for technical assistance. Support by the European Research Council through ERC grant 305003 (QUANTUMsubCYCLE) and by Deutsche Forschungsgemeinschaft (DFG) through Research Training Group GK1570 and KO3612/1-1 is acknowledged.

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Affiliations

  1. Department of Physics, University of Regensburg, D-93040 Regensburg, Germany

    • C. Poellmann
    • , P. Steinleitner
    • , U. Leierseder
    • , P. Nagler
    • , G. Plechinger
    • , M. Porer
    • , C. Schüller
    • , T. Korn
    •  & R. Huber
  2. Institute of Physics, University of Münster, D-48149 Münster, Germany

    • R. Bratschitsch

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Contributions

C.P., R.B., C.S., T.K. and R.H. planned the project; P.N., G.P., R.B., C.S. and T.K. provided, processed and characterized the samples; C.P., P.S., U.L. and M.P. performed the femtosecond measurements; C.P., P.S., U.L., M.P. and R.H. analysed the data; C.P., P.S. and R.H. elaborated the theoretical model; C.P., P.S. and R.H. wrote the paper with contributions from all authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to R. Huber.

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https://doi.org/10.1038/nmat4356

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