Electrons caught flowing like water for the first time (Nanowerk News) We often speak of electrons flowing through materials, but in fact, they do not normally move like a fluid. Such hydrodynamic electron flow had been predicted, though, and Weizmann Institute of Science researchers recently managed, with the help of specially-produced, nanoscopic pipes, to image electrons flowing like the water in household pipes leading to a shower or kitchen sink. This is the first time such liquid electron flow has been visualized, and it has vital implications for future electronic devices.

A river of electrons flowing in a graphene channel. The viscosity generated by the repulsion between electrons (red balls) causes them to flow with a parabolic current density, illustrated here as a white foam wavefront. (Image: Weizmann Institute of Science)

Electron movement through materials  mainly conductors like metals  usually looks more like that of a gas than a fluid. That is, they do not collide with one another, but rather, they tend to bounce off impurities and imperfections in the material. A fluid flow, in contrast, takes it shape  be it waves or whirlpools  from frequent collisions between the particles in the fluid.

To make electrons flow like a fluid, one needs a different kind of conductor, and the team turned to graphene, which is a one-atom-thick sheet of carbon, and which can be made exceptionally clean.

Theories suggest that liquid electrons can perform cool feats that their counterparts cannot. But to get a clear-cut proof that electrons can, indeed, form a liquid state, we wanted to directly visualize their flow, said Prof. Shahal Ilani head of the team in the Institutes Condensed Matter Physics Department.

Even using graphene as a conductor, the team needed to develop a technique that would be both powerful enough to peer inside a material, yet gentle enough to avoid disrupting the electron flow. The Weizmann team created such a technique, as they recently reported in Nature Nanotechnology ("Simultaneous voltage and current density imaging of flowing electrons in two dimensions"). This consists of a nanoscale detector built from a carbon-nanotube transistor, and the team found that can image the properties of flowing electrons with unprecedented sensitivity.

Our technique is at least 1000 times more sensitive than alternate methods; this enables us to image phenomena that previously could only be studied indirectly, say Staff Scientist, Dr. Joseph Sulpizio, in Ilanis lab.

In a new study published in Nature ("Visualizing Poiseuille flow of hydrodynamic electrons"), the Weizmann researchers applied their novel imaging technique to state-of-the-art graphene devices produced in the group of Prof. Andre Geim at the University of Manchester. These devices were microscopic pipes  tiny channels designed to guide the flowing electrons.

The team observed the hallmark signature of hydrodynamic flow: Just like water in a pipe, the electrons in the graphene flowed faster in the center of the channel and slowed down at the walls.

This demonstration  that given the right conditions, electrons can mimic the patterns of a conventional fluid  may prove beneficial for creating new types of electronic devices, including low-power ones in which hydrodynamic flow lowers the electrical resistance.

Computing centers and consumer electronics are devouring an ever increasing amount of energy, and its imperative to find ways to make electrons flow with less resistance, said Dr. Lior Ella, also of Ilanis group.