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Coherent electronic coupling in quantum dot solids induces cooperative enhancement of nonlinear optoelectronic responses

Nature Nanotechnology (2024)Cite this article

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Abstract

Synchronized dynamics of quantum dot (QD) ensembles are essential for generating ultrafast and giant optical responses beyond those of individual QDs. Increasing the strength of the direct electronic coupling between QDs is a key strategy for the realization of cooperative quantum phenomena. Here, we observe a quantum cooperative effect on nonlinear photocurrents caused by the coherent electronic coupling in semiconductor QD solids. We measure quantum interference signals cooperatively generated in QD solids. We control the inter-QD distance with atomic precision using bidentate ligands that strongly link the QDs. The harmonic quantum interference signals are strongly enhanced when shortening the molecular length of the ligand. Furthermore, we clarify that the coherence length of multiexcitons extends to neighbouring QDs. This finding is direct evidence that multiexciton coherent tunnelling assists the ultrafast exciton delocalization. Cooperative enhancement in QD solids may find application in advanced quantum optoelectronics.

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Fig. 1: Sample and experimental setup.
Fig. 2: Quantum interference signals from QD films.
Fig. 3: Harmonic quantum interference signals for different ligand lengths.
Fig. 4: Sources of double-quantum coherent signals.
Fig. 5: Coupling strengths in quantum cooperative processes.
Fig. 6: Correlation of exciton resonance energy and coupling strength.

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The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

Part of this work was supported by JSPS KAKENHI grant nos. JP19H05465 (Y.K. and H.T.), JP22H01990 (H.T.) and JP23K17877 (H.T.), JST-CREST grant no. JPMJCR21B4 (T.T. and Y.K.) and JST-FOREST grant no. JPMJFR201M (M.S.).

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Authors and Affiliations

  1. The Hakubi Center for Advanced Research, Kyoto University, Kyoto, Japan

    Hirokazu Tahara

  2. Institute for Chemical Research, Kyoto University, Uji, Japan

    Hirokazu Tahara, Masanori Sakamoto, Toshiharu Teranishi & Yoshihiko Kanemitsu

Authors
  1. Hirokazu Tahara
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  2. Masanori Sakamoto
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  3. Toshiharu Teranishi
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  4. Yoshihiko Kanemitsu
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Contributions

H.T. conceived and designed the research. H.T. performed the experiments and analysed the data. M.S. and T.T. synthesized the QDs and fabricated the QD films. Y.K. supervised the project. All authors discussed the results and contributed to the writing of the paper.

Corresponding authors

Correspondence to Hirokazu Tahara or Yoshihiko Kanemitsu.

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Nature Nanotechnology thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Optical and electrical properties of QD films.

a, Absorption spectra of C2 (blue), C3 (green), C4 (red), and C5 (black) films. Their normalized spectra are shown in the main text (see Fig. 1c). b, Current-voltage characteristic of a representative C2 film under air mass 1.5 illumination.

Extended Data Fig. 2 Photocurrent quantum interference signals.

Photocurrent quantum interference signals of a C2 film are shown by black solid curves for different excitation photon fluences. The average numbers of absorbed photons per QD are (a) 0.5, (b) 1.1, and (c) 1.7. The photocurrent interference curves show stronger deformations with increasing excitation photon fluence. Excitation pulse interference signals (red dashed curves) were measured simultaneously.

Extended Data Fig. 3 Coupling strengths.

Coupling strengths of (a) \(2\omega\), (b) \(3\omega\), and (c) \(4\omega\) oscillations are plotted as a function of the square root of QD density. The coupling strengths are proportional to the square root of QD density. The QD density is evaluated from the average QD diameter and the lengths of ligand molecules in close packing. Error bars are the standard deviations of the fitting parameters. Dashed curves are guides for the eye.

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Tahara, H., Sakamoto, M., Teranishi, T. et al. Coherent electronic coupling in quantum dot solids induces cooperative enhancement of nonlinear optoelectronic responses. Nat. Nanotechnol. (2024). https://doi.org/10.1038/s41565-024-01601-9

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