Electron Fluid Behavior

While electrons are commonly described as "flowing" in an electric current, their typical movement involves individual particles flying past each other. This differs from water molecules, which move collectively as a coherent fluid. This individualistic particle motion forms the basis of conventional electronic theory, explaining phenomena such as increased resistance in warm wires.

However, since the 1960s, theorists have hypothesized that electrons could be induced to behave more like a fluid, forming an "electron fluid."

Recent experiments have provided empirical support for this prediction.

Recent Discoveries and Experiments

In a recent demonstration, researchers led by Cory Dean at Columbia University observed electrons forming a shock wave. This phenomenon, which occurs when a rapidly flowing fluid collides with a slower one, indicated high-speed electron flow.

This research could potentially lead to the development of new electronic devices and offer a different perspective for understanding quantum materials.

Traditional electron movement through a wire involves collisions with vibrating atoms or impurities, causing them to ricochet and lose momentum. This is similar to water seeping through packed sand. In contrast, water molecules in a pipe primarily collide with each other, conserving momentum, which allows for complex collective motions like eddies and varying flow speeds.

In 1963, Soviet physicist Radii Gurzhi calculated that if electrons conserved momentum during collisions, heat would make them move more readily, unlike the typical impedance seen in copper wires. This "Gurzhi effect" was initially considered a theoretical concept due to impurities in real-world conductors.

Graphene's Role

The discovery of graphene in 2004 by Andre Geim and Konstantin Novoselov provided a material with minimal impurities, making it suitable for studying electron fluid dynamics.

In 2017, Geim and his collaborators conducted an experiment using graphene where resistance decreased as temperature increased, confirming the Gurzhi effect. In 2022, physicists at the Weizmann Institute of Science directly observed electron flow in tungsten diselenide, a graphene-like material, detecting electron whirlpools similar to river eddies.

Supersonic Electron Shock Waves

In 2025, Johannes Geurs, a postdoc in Dean’s lab, investigated creating a supersonic shock wave with electrons, analogous to a sonic boom. He engineered a de Laval nozzle from two sheets of graphene to accelerate electrons.

The electrons were accelerated beyond the "speed of sound" for an electron fluid (hundreds of kilometers per second). When these accelerated electrons interacted with slower electrons downstream, a compression occurred, generating a shock wave.

Researchers detected this by measuring minute changes in the electric field across the sample, confirming that the electron fluid's sound barrier had been broken.