Theoretical Physics: Master's thesis on self-diffusion of particles awarded

In his master's thesis on "Diffusion under the Effect of Lorentz Force" in the field of theoretical physics, TUD student Erik Kalz unveiled a previously undiscovered phenomenon: he shows that in odd-diffusive systems, particle collisions can surprisingly enhance the self-diffusion of particles. A discovery with far-reaching theoretical, experimental and materials science consequences, for which his work was recognized in Springer-Verlag's "BestMasters" series and as an "Editors Suggestion" in the prestigious journal Physical Review Letters.

© Erik Kalz

Physics student Erik Kalz completed his master's thesis in the group of Dr. Abhinav Sharma at the Leibniz Institute of Polymer Research Dresden under the supervision of Prof. Dr. Jens-Uwe Sommer. One of the focal points of the group are so-called odd-diffusive systems. Erik was working on the question of how particles interact with each other in these systems. The theoretical understanding of this interaction is particularly important for describing transport processes, for example in biological physics. As a central concept, Erik investigated the self-diffusion of particles, a statistical quantity that provides information about individual behavior in systems of many comparable particles. "Actually, we expected self-diffusion to decrease with the increase of particle interactions, an intuitively understandable result, because with increase of density and thus of interactions, particles block each other more strongly," explains the young physicist.

However, he was able to demonstrate that particles in odd-diffusive systems showed the opposite behavior: according to this, particle collisions can lead to self-diffusion being enhanced. In these systems, due to an inherent curvature effect, collisions facilitate rather than impede particle motion, leading to mutual rolling around each other. This counterintuitive behavior has been demonstrated by Erik Kalz in the archetypal odd-diffusive system of Brownian particles under the influence of Lorentz force.  "The explanation of the effect has profoundly to do with the tensorial nature of diffusion, in particular the oddness components of the diffusion tensor in these systems. Statistically, particle collisions lead to mutual rolling of the particles, as opposed to mutual blocking, as in normal-diffusing systems," the student explains, and continues, "The discovery has far-reaching consequences in theory, practice, or materials science." As a function of an adjustable system parameter, dynamical transport quantities change into ranges that were previously often thought to be unphysical." Meanwhile, Erik Kalz has startet working as a PhD at the Universität Potsdam.

The student work received a lot of attention in the scientific community. It led to a collaboration with Professor Hartmut Löwen of the Heinrich Heine University in Düsseldorf. In the course of this collaboration, the theoretical prediction was confirmed by simulations, work to which Dr. Sharma's doctoral students, Hidde Vuijk and Iman Abdoli, in particular, contributed. Moreover, the results were published in the prestigious journal Physical Review Letters, and even received an Editors Suggestion. Furthermore, Erik Kalz's master's thesis was selected as one among tens of thousands for Springer-Verlag's BestMasters series, which publishes 30 to 40 master's theses in the fields of natural sciences, psychology, engineering and economics that were written at renowned universities in Germany, Austria and Switzerland.

Original publication:

Kalz, E., Vuijk, H. D., Abdoli, I., Sommer, J. U., Löwen, H. & Sharma, A. (2022). Collisions enhance self-diffusion in odd-diffusive systems. Physical Review Letters, 129(9), 090601. DOI: 10.1103/PhysRevLett.129.090601

Kalz, E. (2022). Diffusion Under the Effect of Lorentz Force. Springer Nature. https://link.springer.com/book/10.1007/978-3-658-39518-6

Contact:
Erik Kalz
Institute of Physics and Astronomy
Universität Potsdam
Email: