For the first time, physicists have pushed electrons to flow so fast through a material that they went supersonic, generating the electronic equivalent of a shockwave. In a new experiment using graphene – an ultra-thin form of carbon – researchers observed electrons behaving like a fluid that suddenly “jumps” just as water does when it transitions from a swift thin stream to a thicker slow flow. This effect, known in fluid dynamics as a hydraulic jump, is akin to the little circular wave you see under a running faucet where fast-moving water abruptly slows down. Now, a Columbia University-led team has achieved a hydraulic jump in an electron flow, essentially creating a tiny electronic sonic boom inside a sheet of graphene. The feat marks a milestone in a growing field called electron hydrodynamics, opening the door to new physics and potentially novel electronic devices.

When Electrons Flow Like Water

In everyday electronics, electric current doesn’t usually behave like a flowing liquid. Electrons typically bump and scatter off atoms in a conductor, more like pinballs than water molecules. This limits how smoothly and quickly they can move. But in certain pure materials and under special conditions, electrons can interact mostly with each other and flow collectively like a fluid.

In 2016, for example, scientists managed to make electrons move through graphene in a viscous, honey-like fashion, exhibiting whirlpools and other hallmarks of fluid flow. Graphene – a single-atom-thick layer of carbon – is an ideal playground for such experiments because it can be made extremely clean, so electrons travel long distances without hitting imperfections. These studies launched the idea of electron hydrodynamics, where currents can mimic behaviors of liquids, from Poiseuille flow (like water through a pipe) to vortices and other fluid phenomena.

However, until now, all electron-fluid experiments were in what scientists call the incompressible or subsonic regime – the electron “liquid” was moving relatively slowly. Researchers had never seen electrons reach the material’s analog of the speed of sound, which is required for more dramatic effects like shockwaves. Scientists had long predicted that if electrons could flow fast enough, electronic shockwaves and other nonlinear effects would appear. But generating and measuring such extreme electron flows is a daunting challenge.

Breaking the Electronic Sound Barrier

That challenge has now been met by Professor Cory Dean and colleagues at Columbia University. In September 2025, they reported using a clever device made from bilayer graphene to accelerate electrons beyond the electron-fluid’s sound speed.

The device is essentially an electronic analog of a de Laval nozzle, a hourglass-shaped conduit famous for its use in rocket engines to accelerate gas to supersonic speeds. In a de Laval nozzle, gas flowing through a narrowing throat can reach sonic speed at the narrowest point; if the gas then expands into a wider section, it accelerates to supersonic velocities instead of slowing down. The research team built a miniature version of this concept for electrons: they created a channel in graphene that first constricts and then expands, all controlled by electric gates.

As electrons flowed through the narrow constriction, they sped up, and upon entering the wider section, they did something unprecedented – they kept accelerating to supersonic flow, then suddenly “choked” and slowed down in a shock beyond the nozzle’s throat.

Crucially, this supersonic electronic flow produced a clear signature of a hydraulic jump – a sharp boundary between fast and slow electron regions – within the graphene device. The electrons went from a high-speed, low-pressure state to a slower, high-pressure (higher electron density) state, analogous to water piling up into a raised rim after flowing rapidly over a surface.

Achieving this electronic shock required exquisitely clean graphene and fine-tuned conditions. The two layers of graphene were encapsulated with other materials to eliminate impurities, and the temperatures were kept low, so that electrons could barrel through like an unhindered fluid. Under these conditions, the electrons’ own mutual interactions dominated their behavior, essentially forcing them to move collectively. As the Columbia team dialed up the flow speed via gate voltages, they witnessed the long-sought transition from subsonic to supersonic electron flow and the emergence of a shock front.

You can read more about the experiment in the original preprint on arXiv.

Seeing a Shockwave Without Sight

How do you observe a shockwave made of invisible electrons? The researchers devised an ingenious way to map the electrical potential landscape in and around the graphene nozzle as the electrons raced through.

They used a technique called Kelvin probe force microscopy (KPFM), which can scan a material’s surface and detect tiny variations in electric potential at nanoscale resolution. This microscope effectively allowed them to “see” the electronic hydraulic jump. What they found was a region in the expanded section of the channel where the local electrochemical potential flattened out abruptly – a telltale sign of a shock, where pressure (here related to electron density and potential) suddenly changes.

At the same time, the overall electrical resistance of the device showed discontinuities when the flow went supersonic, further evidence that the electrons experienced a sudden choke point. These observations matched remarkably well with hydrodynamic theory and computer simulations. The shock appeared as a narrow, stationary jump whose position could be shifted by adjusting the gate voltages – similar to how changing flow conditions moves a hydraulic jump in water.

Importantly, the researchers confirmed that this behavior could not be explained by ordinary electrical conduction or by electrons ballistically shooting through the channel. The presence of the shock unequivocally signaled that the electrons were acting as a compressible fluid, something never seen before in an electronic system.

Crafting a Tiny Electronic Nozzle

Creating the perfect conditions for an electron shockwave required extreme cleanliness and precision in device fabrication. Graphene is only one atom thick, and the nozzle structure had to be shaped and gated with nanometer accuracy.

The Columbia-led team used two layers of graphene, aligning them and carving a channel that tapers to a narrow waist. The bilayer graphene was chosen in part because it allows certain tunabilities (like opening a small band gap with an electric field) and can support strong hydrodynamic effects.

Experts in the field describe the work as a true art: making such a pristine graphene device – where electrons essentially “press against each other” and dominate over collisions with impurities – requires precision and technical mastery. Measuring the tiny shock was equally impressive – the entire jump happened within a channel only a few microns long, yet the team’s mapping was able to resolve this abrupt feature.

The fact that the shock’s position and shape could be controlled by gate voltages is exciting for engineers. It means one could potentially design electronic circuits that harness shockwaves or other nonlinear flow features on demand.

For a broader scientific perspective, see a summary by New Scientist, which highlights how this experiment reshapes our understanding of fluid-like charge motion.

Why Supersonic Electrons Matter

Breaking the electronic sound barrier has practical and scientific implications. For one, it validates that the hydrodynamic approach to electron transport can be pushed into a new “compressible” regime, where density variations and shock effects are important.

This opens up a playground to study nonlinear electron flow phenomena that have no counterpart in traditional electronics. In the compressible (supersonic) regime, entirely new behaviors can emerge – and with them, new questions.

Do charged electron shocks emit any form of radiation? Fluid shocks in air (like sonic booms) create sound waves, and in plasma or charged media they might produce electromagnetic waves. The idea of an electronic shock producing some kind of electromagnetic pulse or terahertz-wave emission has been theorized. One motivation for this line of research is the prospect of developing new terahertz radiation sources. Explore how Supersonic Shock Waves & Electron Fluid dynamics redefine innovation – powered by expert SEO insights for maximum visibility.

Terahertz waves (between infrared and microwave frequencies) have many applications from spectroscopy to security scanning, but they are notoriously hard to generate with conventional electronics. An electron shockwave could potentially be a novel way to generate such high-frequency signals – if it indeed emits them. Professor Dean noted that this question remains open and a bit controversial: experimentalists are keen to detect any radiation from the shock, while some theorists predict that the electron fluid shock shouldn’t radiate.

Beyond radiation, intrinsically nonlinear electronic devices could be envisioned. The researchers themselves highlight that breaking the sound barrier in an electron liquid could lead to new types of electronics that operate on principles very different from ordinary resistors and transistors.

At the very least, this experiment provides a new testbed for fundamental physics, allowing scientists to study how shockwaves form and propagate in a quantum electron medium, bridging quantum mechanics, fluid dynamics, and nanotechnology.

Conclusion: A Sonic Boom on a Chip

By converting an “electron liquid” into a “supersonic gas,” the Columbia-led team has shown that electrons in graphene can mimic not only the smooth flow of honey but also the turbulent dynamics of a rocket exhaust. They created a tiny sonic boom in an electronic circuit – a feat that scientists had been chasing for years.

The work demonstrates a striking example of hydrodynamics and quantum physics colliding – literally, as electron-fluid shockwaves. It expands our understanding of how charge carriers behave when pushed to extreme limits and hints at technological opportunities if we can harness these effects.

As researchers delve deeper into this new supersonic regime, we may see the emergence of electronics that operate with fluid-like shocks and pulses, potentially leading to innovations like on-chip high-frequency wave generators or new logic devices.

One thing is certain: the once purely academic idea of electrons flowing like a fluid has now taken a leap into the supersonic, making the microcosm of graphene even more exciting and wildly rich in phenomena than previously imagined.

Sources

We reference the original scientific preprint “Supersonic flow and hydraulic jump in an electronic de Laval nozzle” (September 25, 2025), available on arXiv.org, as well as reporting by New Scientist and other respected science publications covering advances in condensed matter physics.

The article was prepared by the editorial team of Pacific Outlier.