Clogging can turn a flowing system into a blocked one, but experiments have struggled to establish how that change happens. A Phys.org report published November 11 says researchers at Institute of Science Tokyo found experimental evidence that clogging is a nonequilibrium phase transition, using moving superconducting vortices as a model system.
The team was led by Takahide Minemura, a former graduate student, and Satoshi Okuma, a professor emeritus in the institute’s Department of Physics. Their study, “Clogging transition for vortices driven by dc current,” was published in Communications Physics on September 25, 2026, according to the report.
In a phase transition, a system changes between distinct states. For clogging, the change is from continued motion to a state where movement is obstructed. The report says earlier studies had predicted that this change is a nonequilibrium phase transition: near a critical point, the time needed for a system to settle into either flowing or fully blocked behavior grows sharply. Experimental confirmation had been lacking.
To investigate, the researchers tracked superconducting vortices driven by direct current through thin films made of amorphous molybdenum-germanium. Defects in the material served as pinning sites, where vortices could become trapped. According to the report, trapped vortices could form bottlenecks that obstructed the movement of other vortices, creating clogging.
A central challenge was telling clogging apart from conventional vortex pinning. The researchers used a two-step measurement protocol, applying successive current drives in parallel or opposite directions. They measured voltage as it changed over time to track vortex motion. The report says this let them separate a faster relaxation associated with clogging from a slower relaxation associated with pinning.
As the driving current approached a critical value, both relaxation times increased greatly and followed a power-law divergence, the report says. The critical current for clogging coincided with the depinning current within experimental uncertainty. The critical exponents for the two transitions were also similar to predictions for the two-dimensional directed-percolation universality class, a type of nonequilibrium absorbing phase transition.
Together, those results support a connection between clogging and depinning: the two are distinct dynamical processes, but the researchers found that they share a critical point and show consistent critical behavior. The reported agreement with theoretical predictions is evidence for the proposed transition, while the measurement’s stated experimental uncertainty remains part of the result.
The broader interest is that clogging occurs in many settings, including granular materials, filtration devices, pipelines and biological transport networks. The study does not demonstrate that its findings apply directly to those systems. Instead, the report presents the vortex results as a foundation for future work on clogging in settings such as granular materials, colloids and active matter. It also says future research could examine how the critical dynamics vary across materials and transport environments.
The potential value is better understanding of when flowing systems become obstructed. Whether that understanding can ultimately help predict or control blockages in particular engineered or natural systems remains an open question.