Imaging viscous flow of the Dirac fluid in graphene

Mark J. H. Ku, Tony X. Zhou, Qing Li, Young J. Shin, Jing K. Shi, Claire Burch, Laurel E. Anderson, Andrew T. Pierce, Yonglong Xie, Assaf Hamo, Uri Vool, Huiliang Zhang, Francesco Casola, Takashi Taniguchi, Kenji Watanabe, Michael M. Fogler, Philip Kim, Amir Yacoby () and Ronald L. Walsworth ()
Additional contact information
Mark J. H. Ku: Harvard University
Tony X. Zhou: Harvard University
Qing Li: Harvard University
Young J. Shin: Harvard University
Jing K. Shi: Harvard University
Claire Burch: Harvard University
Laurel E. Anderson: Harvard University
Andrew T. Pierce: Harvard University
Yonglong Xie: Harvard University
Assaf Hamo: Harvard University
Uri Vool: Harvard University
Huiliang Zhang: Harvard University
Francesco Casola: Harvard University
Takashi Taniguchi: National Institute for Materials Science
Kenji Watanabe: National Institute for Materials Science
Michael M. Fogler: University of California, San Diego
Philip Kim: Harvard University
Amir Yacoby: Harvard University
Ronald L. Walsworth: Harvard University

Nature, 2020, vol. 583, issue 7817, 537-541

Abstract: Abstract The electron–hole plasma in charge-neutral graphene is predicted to realize a quantum critical system in which electrical transport features a universal hydrodynamic description, even at room temperature1,2. This quantum critical ‘Dirac fluid’ is expected to have a shear viscosity close to a minimum bound3,4, with an interparticle scattering rate saturating1 at the Planckian time, the shortest possible timescale for particles to relax. Although electrical transport measurements at finite carrier density are consistent with hydrodynamic electron flow in graphene5–8, a clear demonstration of viscous flow at the charge-neutrality point remains elusive. Here we directly image viscous Dirac fluid flow in graphene at room temperature by measuring the associated stray magnetic field. Nanoscale magnetic imaging is performed using quantum spin magnetometers realized with nitrogen vacancy centres in diamond. Scanning single-spin and wide-field magnetometry reveal a parabolic Poiseuille profile for electron flow in a high-mobility graphene channel near the charge-neutrality point, establishing the viscous transport of the Dirac fluid. This measurement is in contrast to the conventional uniform flow profile imaged in a metallic conductor and also in a low-mobility graphene channel. Via combined imaging and transport measurements, we obtain viscosity and scattering rates, and observe that these quantities are comparable to the universal values expected at quantum criticality. This finding establishes a nearly ideal electron fluid in charge-neutral, high-mobility graphene at room temperature4. Our results will enable the study of hydrodynamic transport in quantum critical fluids relevant to strongly correlated electrons in high-temperature superconductors9. This work also highlights the capability of quantum spin magnetometers to probe correlated electronic phenomena at the nanoscale.

Date: 2020
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DOI: 10.1038/s41586-020-2507-2

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