Deciphering clogging dynamics

Clogging is a phenomenon in which moving particles get stuck, slowing or blocking the flow, but how this transition occurs has remained experimentally unproven. Researchers from Science Tokyo studied superconducting vortices to demonstrate that clogging is a nonequilibrium phase transition. Using a two-step measurement protocol, they distinguished clogging from conventional pinning and revealed that both transitions share a critical point, offering new insights into predicting and controlling clogging across diverse systems.

Clogging is a common phenomenon where flowing particles encounter bottlenecks that restrict their passage, slowing down or completely halting movement. This phenomenon is observed across a wide range of systems, including granular materials, filtration devices, industrial pipelines, and biological transport networks. Understanding how and why clogging occurs is essential for preventing blockages and maintaining efficient transport across natural and engineered systems.

Despite its widespread incidence, the physical mechanisms governing the transition from continuous flow to complete clogging remain incompletely understood. Previous studies predicted that this transition represents a nonequilibrium phase transition, in which the time required to reach a stable flowing or completely blocked state diverges near a critical point. However, experimental confirmation of this prediction remained lacking.

Addressing this long-standing question, a research team led by former graduate student Takahide Minemura and Professor Emeritus Satoshi Okuma of the Department of Physics, Institute of Science Tokyo, has provided the first experimental evidence that the widely observed phenomenon of clogging is a nonequilibrium phase transition. This study investigated the critical dynamics of superconducting vortices driven by direct current (DC) and was published in Communications Physics on September 25, 2026.

Okuma explains, “Clogging can also cause serious problems in industrial plants, infrastructure pipelines, and biological transport systems such as blood vessels. Although it has been predicted in simulation that the transition from a flowing state to a completely clogged state represents a nonequilibrium phase transition, experimental verification had remained elusive. This was the main motivation of our study.”

The team examined superconducting vortices moving through amorphous molybdenum-germanium (MoGe) thin films under an applied direct current, where material defects acted as pinning sites. Trapped vortices can form bottlenecks that obstruct the movement of other vortices, producing clogging. To characterize this phenomenon from conventional pinning, they developed a modified two-step measurement protocol involving successive current drives applied in parallel or opposite directions. By measuring the resulting time-dependent voltage, they tracked vortex motion and separated the fast relaxation associated with clogging from the slower relaxation associated with pinning.

The results revealed that both relaxation times increased greatly and adhered to power-law divergence as the driving current approached a critical value. At the same time, the critical current for clogging coincided with the depinning current within experimental uncertainty. Additionally, the critical exponents associated with both transitions were also similar to the predictions for the two-dimensional directed-percolation universality class, which is a type of nonequilibrium absorbing phase transition. These findings demonstrate that clogging and depinning share the same critical point and exhibit consistent critical behavior, even though they represent distinct dynamical processes.

Beyond superconductivity, the findings provide a foundation for understanding clogging across diverse systems. In Okuma’s words, “Understanding, predicting, and controlling clogging is important across scientific and engineering disciplines. The findings of our study may help guide future studies of flow obstruction in granular materials, colloids, active matter, and other systems in which collective motion can become blocked.”

In the future, further research could explore how these critical dynamics vary across different materials and transport environments. Ultimately, a deeper understanding of the transition from flow to blockage could support more effective strategies for anticipating and controlling clogging in industrial processes, infrastructure, and biological transport systems.

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About Institute of Science Tokyo (Science Tokyo)

Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”