Letter | Published:

Lightwave-driven quasiparticle collisions on a subcycle timescale

Nature volume 533, pages 225229 (12 May 2016) | Download Citation

Abstract

Ever since Ernest Rutherford scattered α-particles from gold foils1, collision experiments have revealed insights into atoms, nuclei and elementary particles2. In solids, many-body correlations lead to characteristic resonances3—called quasiparticles—such as excitons, dropletons4, polarons and Cooper pairs. The structure and dynamics of quasiparticles are important because they define macroscopic phenomena such as Mott insulating states, spontaneous spin- and charge-order, and high-temperature superconductivity5. However, the extremely short lifetimes of these entities6 make practical implementations of a suitable collider challenging. Here we exploit lightwave-driven charge transport7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24, the foundation of attosecond science9,10,11,12,13, to explore ultrafast quasiparticle collisions directly in the time domain: a femtosecond optical pulse creates excitonic electron–hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying dynamics of the wave packets, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands17,18,19 of the optical excitation. A full quantum theory explains our observations microscopically. This approach enables collision experiments with various complex quasiparticles and suggests a promising new way of generating sub-femtosecond pulses.

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Acknowledgements

We thank H. Banks for critical reading of the manuscript. The work in Regensburg was supported by the European Research Council through grant number 305003 (QUANTUMsubCYCLE) and the Deutsche Forschungsgemeinschaft (through grant number HU 1598/2-1 and GRK 1570), and the work in Marburg by the Deutsche Forschungsgemeinschaft (through SFB 1083, SPP 1840 and grant numbers KI 917/2-2, KI 917/3-1). The work in Santa Barbara was supported by the National Science Foundation (through grant number DMR 1405964).

Author information

Affiliations

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

    • F. Langer
    • , M. Hohenleutner
    • , C. P. Schmid
    • , C. Poellmann
    • , P. Nagler
    • , T. Korn
    • , C. Schüller
    •  & R. Huber
  2. Department of Physics and the Institute for Terahertz Science and Technology, University of California at Santa Barbara, Santa Barbara, California 93106, USA

    • M. S. Sherwin
  3. Department of Physics, University of Marburg, 35032 Marburg, Germany

    • U. Huttner
    • , J. T. Steiner
    • , S. W. Koch
    •  & M. Kira

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Contributions

F.L., M.H., M.S.S., U.H., M.K. and R.H. conceived the study. F.L., M.H., C.P.S. and R.H. carried out the experiment and analysed the data. C.P., P.N., T.K. and C.S. provided, processed and characterized the samples. U.H., J.T.S., S.W.K. and M.K. developed the quantum-mechanical model and carried out the computations. All authors discussed the results and contributed to the writing of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to M. Kira or R. Huber.

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https://doi.org/10.1038/nature17958

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