Observation of hydrodynamic plasmons and energy waves in graphene

Wenyu Zhao; Shaoxin Wang; Sudi Chen; Zuocheng Zhang; Kenji Watanabe; Takashi Taniguchi; Alex Zettl; Feng Wang

doi:10.1038/s41586-022-05619-8

Observation of hydrodynamic plasmons and energy waves in graphene

Nature. 2023 Feb;614(7949):688-693. doi: 10.1038/s41586-022-05619-8. Epub 2023 Feb 22.

Authors

Wenyu Zhao^#¹, Shaoxin Wang^#^{1

2}, Sudi Chen^{3

4}, Zuocheng Zhang¹, Kenji Watanabe⁵, Takashi Taniguchi⁶, Alex Zettl^{1

3

4

7}, Feng Wang^{8

9

10

11}

Affiliations

¹ Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
² Graduate Group in Applied Science and Technology, University of California at Berkeley, Berkeley, CA, USA.
³ Kavli Energy NanoScience Institute, University of California at Berkeley, Berkeley, CA, USA.
⁴ Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁵ Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan.
⁶ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
⁷ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁸ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. fengwang76@berkeley.edu.
⁹ Kavli Energy NanoScience Institute, University of California at Berkeley, Berkeley, CA, USA. fengwang76@berkeley.edu.
¹⁰ Lawrence Berkeley National Laboratory, Berkeley, CA, USA. fengwang76@berkeley.edu.
¹¹ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. fengwang76@berkeley.edu.

^# Contributed equally.

PMID: 36813893
DOI: 10.1038/s41586-022-05619-8

Abstract

Thermally excited electrons and holes form a quantum-critical Dirac fluid in ultraclean graphene and their electrodynamic responses are described by a universal hydrodynamic theory. The hydrodynamic Dirac fluid can host intriguing collective excitations distinctively different from those in a Fermi liquid^1-4. Here we report the observation of the hydrodynamic plasmon and energy wave in ultraclean graphene. We use the on-chip terahertz (THz) spectroscopy technique to measure the THz absorption spectra of a graphene microribbon as well as the propagation of the energy wave in graphene close to charge neutrality. We observe a prominent high-frequency hydrodynamic bipolar-plasmon resonance and a weaker low-frequency energy-wave resonance of the Dirac fluid in ultraclean graphene. The hydrodynamic bipolar plasmon is characterized by the antiphase oscillation of massless electrons and holes in graphene. The hydrodynamic energy wave is an electron-hole sound mode with both charge carriers oscillating in phase and moving together. The spatial-temporal imaging technique shows that the energy wave propagates at a characteristic speed of [Formula: see text] near the charge neutrality^2-4. Our observations open new opportunities to explore collective hydrodynamic excitations in graphene systems.

Publication types

Research Support, U.S. Gov't, P.H.S.
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Abstract

Publication types

Grants and funding