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.
| Original language | English |
|---|---|
| Pages (from-to) | 537-541 |
| Number of pages | 5 |
| Journal | Nature |
| Volume | 583 |
| Issue number | 7817 |
| DOIs | |
| State | Published - 23 Jul 2020 |
| Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2020, The Author(s), under exclusive licence to Springer Nature Limited.
Funding
Acknowledgements We thank B. Narozhny for helpful discussions, M. J. Turner for annealing diamond samples and S. Y. F. Zhao for assisting with the magneto-transport measurement. This material is based on work supported by, or in part by, the United States Army Research Laboratory and the United States Army Research Office under contract/grant number W911NF1510548 and number W911NF1110400, as well as the Quantum Technology Center (QTC) at the University of Maryland. A.T.P. and Y.X. were primarily supported by the US Department of Energy, Basic Energy Sciences Office, Division of Materials Sciences and Engineering under award DE-SC0001819. T.X.Z., A.H. and U.V. were partly supported by ARO grant number W911NF-17-1-0023 and the Gordon and Betty Moore Foundations EPiQS Initiative through grant number GBMF4531. Fabrication of samples was supported by the US Department of Energy, Basic Energy Sciences Office, Division of Materials Sciences and Engineering under award DE-SC0019300. A.Y. also acknowledges support from ARO grants W911NF-18-1-0316 and W911NF-1-81-0206 and the STC Center for Integrated Quantum Materials, NSF grant number DMR-1231319. Part of this work was supported under the NSF grant number EFMA 1542807; and the Elemental Strategy Initiative conducted by MEXT, Japan, and JSPS KAKENHI grant JP15K21722 (K.W. and T.T.). Finally, this work was partly carried out at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. F.C. acknowledges partial support from the Swiss National Science Foundation grant number P300P2-158417. P.K. acknowledges support from ARO (W911NF-17-1-0574). M.M.F. acknowledges support from the Office of Naval Research grant N00014-18-1-2722. A.T.P. acknowledges support from the Department of Defense through the National Defense Science and Engineering Graduate Fellowship (NDSEG) Program. Y.X. acknowledges partial support from the Harvard Quantum Initiative in Science and Engineering. This research used resources of the Center for Functional Nanomaterials, which is a US DOE Office of Science Facility, at Brookhaven National Laboratory under contract number DE-SC0012704. This work was performed, in part, at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network, which is supported by the NSF under award no. ECS-0335765. CNS is part of Harvard University.
| Funders | Funder number |
|---|---|
| Basic Energy Sciences Office | |
| Harvard Quantum Initiative in Science and Engineering | |
| STC Center for Integrated Quantum Materials | |
| US Department of Energy | |
| National Science Foundation | DMR-1231319, PHY-1607611, EFMA 1542807 |
| U.S. Department of Defense | |
| Office of Naval Research | N00014-18-1-2722 |
| Army Research Office | W911NF-17-1-0023, W911NF1110400, W911NF1510548 |
| Gordon and Betty Moore Foundation | DE-SC0019300, GBMF4531, W911NF-1-81-0206, W911NF-18-1-0316 |
| Office of Science | |
| Brookhaven National Laboratory | ECS-0335765, DE-SC0012704 |
| Army Research Laboratory | |
| University of Maryland | |
| Division of Materials Sciences and Engineering | DE-SC0001819 |
| National Defense Science and Engineering Graduate | |
| Japan Society for the Promotion of Science | JP15K21722 |
| Ministry of Education, Culture, Sports, Science and Technology | |
| Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung | W911NF-17-1-0574, P300P2_158417 |