Physicists see fluid-like electron whirlpools for the first time

Amazing stuff!

"... Now, physicists ... have observed electrons flowing in vortices, or whirlpools — a hallmark of fluid flow that theorists predicted electrons should exhibit, but that has never been seen until now. ...
“We know when electrons go in a fluid state, [energy] dissipation drops, and that’s of interest in trying to design low-power electronics,” ...
This liquid-like behavior should emerge in ultraclean materials and at near-zero temperatures. ...
In 2017, ... reported signatures of such fluid-like electron behavior in graphene, an atom-thin sheet of carbon onto which they etched a thin channel with several pinch points. They observed that a current sent through the channel could flow through the constrictions with little resistance. This suggested that the electrons in the current were able to squeeze through the pinch points collectively, much like a fluid, rather than clogging, like individual grains of sand. ...
tungsten ditelluride (WTe2), an ultraclean metallic compound that has been found to exhibit exotic electronic properties when isolated in single-atom-thin, two-dimensional form. ...
The group’s observations are the first direct visualization of swirling vortices in an electric current. The findings represent an experimental confirmation of a fundamental property in electron behavior. ..."

From the abstract:

"Vortices are the hallmarks of hydrodynamic flow. Strongly interacting electrons in ultrapure conductors can display signatures of hydrodynamic behaviour, including negative non-local resistance, higher-than-ballistic conduction, Poiseuille flow in narrow channels and violation of the Wiedemann–Franz law. Here we provide a visualization of whirlpools in an electron fluid. By using a nanoscale scanning superconducting quantum interference device on a tip, we image the current distribution in a circular chamber connected through a small aperture to a current-carrying strip in the high-purity type II Weyl semimetal WTe2. In this geometry, the Gurzhi momentum diffusion length and the size of the aperture determine the vortex stability phase diagram. We find that vortices are present for only small apertures, whereas the flow is laminar (non-vortical) for larger apertures. Near the vortical-to-laminar transition, we observe the single vortex in the chamber splitting into two vortices; this behaviour is expected only in the hydrodynamic regime and is not anticipated for ballistic transport. These findings suggest a new mechanism of hydrodynamic flow in thin pure crystals such that the spatial diffusion of electron momenta is enabled by small-angle scattering at the surfaces instead of the routinely invoked electron–electron scattering, which becomes extremely weak at low temperatures. ..."

Physicists see electron whirlpools for the first time | MIT News | Massachusetts Institute of Technology Long predicted but never observed, this fluid-like electron behavior could be leveraged for low-power next-generation electronics.

Direct observation of vortices in an electron fluid (no public access)

In most materials like gold (left), electrons flow with the electric field. But MIT physicists have found that in exotic tungsten ditelluride (right), the particles can reverse direction and swirl like a liquid.