Steady Floquet-Andreev States in graphene Josephson junction

ORAL

Abstract

Engineering quantum states through light–matter interaction has created a paradigm in condensed-matter physics. A representative example is the Floquet–Bloch state, which is generated by time-periodically driving the Bloch wavefunctions in crystals. Previous attempts to realize such states in condensed-matter systems have been limited by the transient nature of the Floquet states produced by optical pulses, which masks the universal properties of non-equilibrium physics. Here we report the generation of steady Floquet–Andreev states in graphene Josephson junctions by continuous microwave application and direct measurement of their spectra by superconducting tunnelling spectroscopy. We present quantitative analysis of the spectral characteristics of the Floquet–Andreev states while varying the phase difference of the superconductors, the temperature, the microwave frequency and the power. The oscillations of the Floquet–Andreev-state spectrum with phase difference agreed with our theoretical calculations. Moreover, we confirmed the steady nature of the Floquet–Andreev states by establishing a sum rule of tunnelling conductance, and analysed the spectral density of Floquet states depending on Floquet interaction strength. This study provides a basis for understanding and engineering non-equilibrium quantum states in nanodevices.

*Samsung Science and Technology Foundation, National Research Foundation of Korea, So-Seon Na-Num Foundation

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Publication: Park, S., Lee, W., Jang, S. et al. Steady Floquet–Andreev states in graphene Josephson junctions. Nature 603, 421–426 (2022). https://doi.org/10.1038/s41586-021-04364-8

Presenters

  • Sein Park

    • Pohang Univ of Sci & Tech

Authors

  • Sein Park

    • Pohang Univ of Sci & Tech

  • Wonjun Lee

    • Pohang Univ of Sci & Tech

  • Seong Jang

    • Pohang Univ of Sci & Tech
    • Postech

  • Yong-Bin Choi

    • Pohang Univ of Sci & Tech

  • Jinho Park

    • Raytheon BBN Technologies

  • Woochan Jung

    • Pohang Univ of Sci & Tech

  • Kenji Watanabe

    • National Institute for Materials Science
    • Research Center for Functional Materials, National Institute of Materials Science
    • Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-044, Japan
    • NIMS
    • Research Center for Functional Materials, National Institute for Materials Science
    • National Institute for Materials Science, Japan
    • Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
    • NIMS Japan

  • Takashi Taniguchi

    • National Institute for Materials Science
    • Kyoto Univ
    • International Center for Materials Nanoarchitectonics, National Institute of Materials Science
    • Kyoto University
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-044, Japan
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science
    • National Institute for Materials Science, Japan
    • National Institute For Materials Science
    • NIMS
    • National Institute for Material Science
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
    • NIMS Japan

  • Gil Young Cho

    • Pohang University of Science and Technology, Asia-Pacific Center for Theoretical Physics, Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science
    • Pohang Univ of Sci & Tech

  • Gil-Ho Lee

    • Pohang Univ of Sci & Tech