Evidence for hydrodynamic electron flow in PdCoO$_2$

Understand

Electron transport is conventionally determined by the momentum-relaxing scattering of electrons by the host solid and its excitations.

• The electrical resistance is set by geometrical factors and the resistivity, which is a microscopic property of the solid.
• Hydrodynamic fluid flow through channels, in contrast, is determined by geometrical factors, boundary scattering and the viscosity of the fluid, which is governed by momentum-conserving internal collisions.
• A long-standing question in the physics of solids, brought into focus by the advent of new calculational techniques, has been whether the viscosity of the electron fluid plays an observable role in determining the resistance.