Observation of multi-directional energy transfer in a hybrid plasmonic-excitonic nanostructure

Authors:
  • TVThomas Vasileiadis
    Thomas Vasileiadis
  • SDShuo Dong
    Shuo Dong
  • SBSamuel Beaulieu
    Samuel Beaulieu
  • MDMaciej Dendzik
    Maciej Dendzik
  • DZDaniela Zahn
    Daniela Zahn
  • SLSang-Eun Lee
    Sang-Eun Lee
  • HSHélène Seiler
    Hélène Seiler
  • YQYinpeng Qi
    Yinpeng Qi
  • RPR Patrick
    R Patrick
  • XMXian Maklar
    Xian Maklar
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Abstract
Hybrid plasmonic devices involve a nanostructured metal supporting localized surface plasmons to amplify light-matter interaction, and a non-plasmonic material to functionalize charge excitations. Application-relevant epitaxial heterostructures, however, give rise to ballistic ultrafast dynamics that challenge the conventional semiclassical understanding of unidirectional nanometal-to-substrate energy transfer. We study epitaxial Au nanoislands on WSe$_2$ with time- and angle-resolved photoemission spectroscopy and femtosecond electron diffraction: this combination of techniques resolves material, energy and momentum of charge-carriers and phonons excited in the heterostructure. We observe a strong non-linear plasmon-exciton interaction that transfers the energy of sub-bandgap photons very efficiently to the semiconductor, leaving the metal cold until non-radiative exciton recombination heats the nanoparticles on hundreds of femtoseconds timescales. Our results resolve a multi-directional energy exchange on timescales shorter than the electronic thermalization of the nanometal. Electron-phonon coupling and diffusive charge-transfer determine the subsequent energy flow. This complex dynamics opens perspectives for optoelectronic and photocatalytic applications, while providing a constraining experimental testbed for state-of-the-art modelling.