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JOŽEF STEFAN INSTITUTE
Department of Complex Matter
Jamova cesta 39, 1000 Ljubljana, Slovenia

Dynamics of Quantum matter

We explore non-equilibrium many-body dynamics in quantum systems that experience symmetry-breaking, topological, or jamming transitions. These systems encompass superconductors, charge-density wave, and magnetic materials.

Experimental Soft Matter Physics

The research is conducted within the “Light and Matter” research program. The interaction of light with matter is one of the most important fields of physics and optical processes are indispensable in many branches of modern industry.

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February 6, 2024
The absence of efficient light modulators for extreme ultraviolet - EUV and X-ray photons considerably limits their real-life application, particularly when even slight complexity of the beam patterns is required. In ...

Home / Experimental Soft Matter Physics / Active colloidal systems

Active colloidal systems

We study active colloidal systems in the form of magnetically and electrically driven micro- and nanoparticles. Activity-induced self-organisation is observed and investigated in dense particle suspensions or large groups. Optical tweezers enable active microrheology measurements and microfluidic prototypes allow us to perform experiments in complex geometries. We discover design rules for potential application of active colloidal systems in fields such as microfluidics or microrobotics.

 

Symmetry breaking in ferromagnetic ferrofluids

 

Sufficiently dense dispersions of magnetic discoidal nanoparticles form a ferromagnetic nematic phase. When placed in an oscillating magnetic field, we observe a peculiar spontaneous formation of highly periodic striped structures in the direction perpendicular to the magnetic field. The stripes,  identified as elongated magnetic domains, are separated by lines, along which fluid flow is observed. The fluid in adjacent lanes moves in the opposite directions despite the applied magnetic field being uniform. The formation of such bidirectional flow lanes can be explained by alternating rotation of magnetic nanoparticles in neighbouring stripes, which can be explained only by spontaneous breaking of the chiral symmetry.

Vilfan, M., Lampret, B., Gregorin, Ž., Cmok, L., Vilfan, A., Klepp, J., Kohlbrecher, J., Hribar Boštjančič, P., Lisjak, D. and Mertelj, A., 2023. Spontaneous chiral symmetry breaking and lane formation in ferromagnetic ferrofluids. Small, 19(52), p.2304387. (doi: 10.1002/smll.202304387)

 

Activity driven moving droplets

 

Large electric fields exploit the Quincke effect in leaky-dielectrics to initiate spontaneous rolling of plastic microspheres. The rolling direction is selected randomly by each particle and when we have hundreds of them near each other they collide and interact hydrodynamically. This leads to spontaneous organization of particles to form flocks and vortices. Additionally, we confine the particles within a soft boundary of a quasy-twodimensional droplet. We have demonstrated activity controled boundary fluctuations and discovored spontanoues droplet locomotion events, where the droplet deforms perpendicular to the direction of travel.

Kokot, G., Faizi, H.A., Pradillo, G.E., Snezhko, A. and Vlahovska, P.M., 2022. Spontaneous self-propulsion and nonequilibrium shape fluctuations of a droplet enclosing active particles. Communications Physics, 5(1), p.91. (doi: 10.1038/s42005-022-00872-9 )