Electrons can be very hot even if the crystal is close to absolute zero
At the edge of absolute zero, physicists at McGill University and the National Research Council of Canada have coaxed electrons through crystals only atoms thick, drawing from them something the prevailing theory said they should not produce: controlled bursts of quantum sound. The discovery does not merely add a capability — it quietly unsettles the models physicists have long used to describe how energy moves inside matter. In revealing that electrons can run hot even within a nearly frozen crystal, the work opens a passage toward technologies that travel where light and electricity cannot: through water, through tissue, through the body itself.
- Existing theoretical models cannot fully account for the volume of phonons being generated, forcing a reassessment of how energy behaves inside advanced materials.
- The device operates at temperatures approaching absolute zero — a regime so extreme that electrons abandon ordinary behavior and begin moving in coherent, wave-like patterns.
- Researchers discovered that phonon generation continues well beyond the electron speed thresholds theory once treated as necessary conditions, a result that surprised even the team.
- By demonstrating repeatable, controllable phonon bursts, the team has cleared the foundational hurdle that separates a laboratory curiosity from a buildable technology.
- Testing with graphene is the immediate next step, with the goal of pushing the device toward higher temperatures and practical operating conditions.
A team of physicists has built a device that does something prevailing theory said should not happen — at least not the way it is happening. By driving electrons through a crystal only a few atoms wide, cooled to within a whisper of absolute zero, they coaxed those electrons into releasing their energy as precisely controlled bursts of quantum sound particles called phonons. The complication: the electrons produced far more phonons than existing models predict they should.
The work emerged from McGill University and the National Research Council of Canada, with the crystal material synthesized at Princeton. What makes it significant is not only that phonons behaved predictably, but that they did so in a physical regime where the standard rules appear to break down. As McGill physicist Michael Hilke points out, sound travels where light and electrical current cannot — through water, through the human body — making quantum sound a potentially transformative tool for medical imaging, sensing, and communications.
The device is conceptually spare: a two-dimensional crystal confines electrons to a narrow channel, and as current drives them through at speed, they shed excess energy as phonons. The experiments ran at temperatures between 10 millikelvin and 3.9 Kelvin, cold enough that electrons move in orderly, wave-like patterns. Classical theory holds that phonons should not form unless electrons reach the speed of sound. Hilke's team pushed well past that threshold and found phonons generating regardless.
The key insight is a striking disconnect: the electrons in this device are energetically hot — fast-moving, energy-laden — even as the surrounding crystal sits nearly frozen. That gap forces physicists to reconsider how energy transforms inside advanced materials. If phonons can be generated reliably, the path forward includes phonon lasers, communication systems resilient to environments where conventional electronics fail, and medical tools of unprecedented sensitivity. The next step is graphene, which may allow the device to operate at higher temperatures. The deeper question, now that the possibility is established, is simply how far it can be pushed.
A team of physicists has built a device that does something the textbooks said shouldn't happen—at least not the way it's happening. By forcing electrons through a crystal so thin it's only a few atoms wide, and cooling the whole apparatus to near absolute zero, they've managed to coax the electrons into releasing their energy as precisely controlled bursts of quantum sound. The catch: the electrons are generating far more of these sound-like particles, called phonons, than existing theory predicts they should.
The work was done at McGill University and the National Research Council of Canada, with the crystal material itself synthesized at Princeton. What makes this significant isn't just that they got phonons to behave predictably—it's that they did it in a regime where the physics shouldn't work the way it does. Michael Hilke, an associate professor of physics at McGill and one of the study's authors, explains the practical appeal: while light and electrical currents can't travel through water, sound can. The same goes for the human body, where sound waves have proven useful for imaging and treatment. A technology that harnesses quantum sound could open doors that light-based systems simply can't.
The device itself is elegantly simple in concept. A two-dimensional crystal acts as a channel, confining electrons to a path only a few atoms across. When electrical current pushes these electrons through at high speed, they shed excess energy as phonons—vibrations that behave like particles. The researchers discovered they could generate these phonons in repeatable, controllable patterns, a prerequisite for any practical technology that depends on manipulating sound at the quantum scale.
The experiments ran at temperatures between 10 millikelvin and 3.9 Kelvin—so cold that electrons behave in orderly, wave-like ways rather than as ordinary particles bouncing around. This is where quantum physics takes over from classical mechanics. Hilke notes that conventional theory holds that phonons shouldn't be created unless electrons are traveling at or above the speed of sound. His team pushed well beyond that threshold and found phonons being generated anyway. "Earlier work had observed related effects as electron speeds approached the sound barrier," Hilke said. "Our study goes further by pushing the system well beyond that point and showing that existing theories need to be reassessed by considering that electrons can be very hot even if the host crystal is close to absolute zero temperature."
That last phrase captures something crucial: the electrons in this device are hot—they're moving fast, carrying lots of energy—even though the crystal around them is nearly frozen solid. It's a disconnect that forces physicists to reconsider how energy moves and transforms inside advanced materials. The implications ripple outward. If you can generate phonons reliably, you might build a phonon laser. You might create communication systems that work in environments where conventional electronics fail. You might develop medical imaging tools or sensing systems that operate with unprecedented sensitivity.
The next phase involves testing the device with other materials, particularly graphene, which could allow it to operate at higher temperatures and potentially higher speeds. Hilke frames the work in deliberately broad terms: "At a broad level, this is about how electrical current and energy moves and is converted inside advanced electronic materials." That's the real frontier. Phonons are notoriously difficult to generate and control. This device shows it's possible. The question now is how far you can push it, and what you can build once you do.
Citas Notables
In a medium such as oceans, sound can travel, whereas light and electrical currents cannot. In the human body, sound waves can also be a useful tool.— Michael Hilke, Associate Professor of Physics, McGill University
Existing theories need to be reassessed by considering that electrons can be very hot even if the host crystal is close to absolute zero temperature.— Michael Hilke
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter that phonons are being generated at all, let alone in these controlled bursts?
Because phonons are the quantum version of sound, and sound travels where light can't. In water, in tissue, in environments where electromagnetic signals fail—sound gets through. If you can generate and control phonons reliably, you've unlocked a new channel for information and energy.
But the electrons are hot and the crystal is cold. That seems contradictory.
It is, in a way. The electrons are moving fast, carrying kinetic energy. The crystal lattice itself is nearly frozen. So you have this collision of scales—hot particles in a cold medium—and that's where the unexpected physics emerges. It's forcing theorists to rethink their models.
What does "beyond theoretical predictions" actually mean here? Did the theory fail?
Not fail, exactly. The theory said phonons shouldn't be generated at these electron speeds. But they are. So either the theory is incomplete, or it's missing something about how electrons behave in these extreme conditions. That's the honest answer: we don't fully understand what's happening yet.
What's the practical timeline? When do we see phonon lasers or quantum communications?
That's the hard part. This is fundamental research. The next step is testing with graphene and other materials to see if the effect is robust. Then you'd need to engineer actual devices. Years, probably. But the foundation is there now.
Why does temperature matter so much?
At room temperature, electrons are chaotic—bouncing around, interfering with each other. Near absolute zero, they move in concert, almost like a single entity. That's when quantum effects become visible and controllable. It's the difference between watching individual raindrops and watching a coordinated wave.