title: Evidence for hydrodynamic electron flow in PdCoO₂.
abstract: Electron transport is conventionally determined by the momentum-relaxing scattering of electrons by the host solid and its excitations. Hydrodynamic fluid flow through channels, in contrast, is determined partly by the viscosity of the fluid, which is governed by momentum-conserving internal collisions. A long-standing question in the physics of solids has been whether the viscosity of the electron fluid plays an observable role in determining the resistance. We report experimental evidence that the resistance of restricted channels of the ultrapure two-dimensional metal palladium cobaltate (PdCoO2) has a large viscous contribution. Comparison with theory allows an estimate of the electronic viscosity in the range between 6 × 10(-3) kg m(-1) s(-1) and 3 × 10(-4) kg m(-1) s(-1), versus 1 × 10(-3) kg m(-1) s(-1) for water at room temperature.
authors.affiliation: Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland. Department of Physics, University of California, Berkeley, CA 94720, USA. Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Philip J W
authors.initials: PJ
authors.lastname: Moll
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Pallavi
authors.initials: P
authors.lastname: Kushwaha
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Nabhanila
authors.initials: N
authors.lastname: Nandi
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Burkhard
authors.initials: B
authors.lastname: Schmidt
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany. Scottish Universities Physics Alliance, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, UK. andy.mackenzie@cpfs.mpg.de.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Mackenzie