Prof. Dr. Matthias Krüger

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Non-equilibrium Statistical Physics

(Quantum-)thermal fluctuations are a fundamental part of our world, as they influence our daily observed surroundings in many ways. In equilibrium, such fluctuations are well understood in the framework of statistical physics and thermodynamics. In non-equilibrium, however, many of the helpful tools and theorems, employed for equilibrium systems, are not applicable. This makes non-equilibrium on the one hand harder to understand and treat theoretically, but on the other hand often richer in phenomenology and possibilities. Our group aims at improving both the theoretical description and understanding of non-equilibrium fluctuations, mostly in the following fields.

In quantum electrodynamics, we investigate effects which are mediated by the fluctuating electromagnetic field, namely radiative heat transfer and Casimir interactions. Read here about our work on transfer within media (to appear in Phys. Rev. Lett.), and propulsion forces via the Casimir effect. To continue the studies, we have just been awarded a grant by the Volkswagen Foundation.

We investigate the stochastic motion of Brownian particles in fluids with nonlinear and non-Markovian properties, supported by the DFG within SFB1432. Read more about the Magnus effect in such fluids, and a linear response formula. We developed a general nonlinear Langevin equation here.

We investigate (de)mixing dynamics in fluids with many components, supported by the DFG. See here our work on the role of the mobility.

Supported by the DFG in SFB1073, we investigate the frictional damping of a small probe moving on or over solid surfaces. Please read our article on the role of layer-structuring of the surface. From this work, one can learn how deep friction "feels" into the solid.

When Brown discovered Brownian motion in 1827, he expected to see motion of living entities. How could he have known that he saw thermal fluctuations? This question is still not settled. We introduced a new observable, the Mean Back Relaxation (MBR), accepted in Nat. Mat. ("in principle"). We can show that it is a marker for broken detailed balance in confinement. In a later work, we introduce MBR for microscopic densities, which is a marker for broken detailed balance in confinement and in bulk systems.