Marine Le Blay, Joshua Saldi, and Alexandre Morin of Leiden University have made a deeply significant find. Their work represents a major conceptual shift for the active matter physics field. Their discoveries hinge on the strange group dynamics that take place when a bunch of particles get all squished together. The team had a thrilling find on their hands. What they discovered is that the beads, sandwiched between two glass plates acting as electrodes, exhibit a novel state of matter characterized by energy flow through impacts.
The researchers performed lab experiments by increasing the number of beads to hundreds and thousands, yielding curious and incredible results. Once the beads reached a certain density, they began to move around chaotically. They darted to and fro across the glass plates at mind-boggling speeds—up to 100x per second! This high-energy experimental context provides a truly unique opportunity to do a close-up study of what these tiny, interacting particles are doing.
Experimentation and Observation
Alexandre Morin discussed the experimental procedure, and explained how exacting the process was for the team.
“While the beads move around, we take 300 to 400 images per second with our high-speed camera. We then make slow-motion videos of these images to discover in detail what is happening. We link every particle from one image to the next and make precise statistics of the movements observed. One afternoon of experimenting can fill up an entire hard drive. We use a strong computer and an efficient analysis routine to do this work.” – Alexandre Morin
This detailed, complex gathering of data allows researchers to document the delicate behaviors of the beads. Then other researchers can repeat the procedure to study how these beads behave in various conditions. Their state of the art application of technology allows them to develop understandings into the basic building blocks of how things move and come together.
Control and Manipulation of Particle Behavior
Experiments in part by the Hu lab revealed the existence of a previously unknown state of matter. They stumbled upon a new way to tune how those individual metal balls acted as a group.
“Once we understood how these packed particles power up, we realized that we could even control the collective behavior of the metal beads,” – Alexandre Morin
By changing the energy they fed to the particles, they found that they could actually control their movements in dramatic ways. Rather than supplying a steady current, they played with pulsed electric fields, turning the power on and off.
“To do so, instead of powering the particles continuously, we powered them intermittently by switching the electric field on and off. We observed that the faster the switching, the slower the movements. But more importantly, the structure of the group also changed.” – Alexandre Morin
This manipulation allows much deeper insight into how varying states of energy can influence the order or disorder of the arrangement of particles. The authors have shown an exciting finding. By adjusting parameters on their 3D printer, they’re able to design structures that resemble the forms of gas, liquid, and crystal.
Implications of the Discovery
This study has broader implications that stretch well beyond academic interest. In addition to addressing many questions in particle physics, it is opening up promising new investigations in material science.
“This is an important discovery because it reveals that there are still many unknown ways in which particles can organize themselves,” – Alexandre Morin
The basic knowledge gained from this process might be utilized in any other fields similar to material design or nanotechnology. Through the application of these principles, scientists will be able to design new materials with customized properties designed for specialized applications.
They have published the resulting research in full in their recent publication, available online via DOI 10.1038/s41567-025-02957-y.