Regensburg 2022 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 40: Brownian Motion and Anomalous Diffusion

DY 40.2: Vortrag

Donnerstag, 8. September 2022, 10:15–10:30, H20

Ballistic Hot Brownian Motion — •Xiaoya Su¹, Frank Cichos¹, and Klaus Kroy² — ¹Peter Debye Institute for Soft Matter Physics, University Leipzig, Leipzig, Germany — ²Institute of Theoretical Physics, University Leipzig, Leipzig, Germany

Brownian motion is the erratic motion of particles in a fluid due to the bombardment of the particle with solvent molecules providing thermal energy and viscous friction. It is fundamental for the dynamics of soft matter and defines the prototype of a fluctuation dissipation relation. While at long timescales the motion is purely stochastic, it is at shorter times influenced by hydrodynamic effects and even ballistic at ultrashort timescales. Yet, the ballistic motion, same as the stochastic motion, is still determined by the temperature of the system. Here we explore the transition to the ballistic regime for a hot Brownian particle, i.e. a microparticle which is heated by a laser in an optical trap. In this case the particle temperature is different from the solvent temperature and so far, only theoretical predictions exist for the relevant temperature determining the particle velocity.

We report the first measurements of the thermal non-equilibrium process in a specially designed optical trap which is able to resolve particle displacements of about 20 pm with a time-resolution of 10ns. We show how the mean squared displacement of the particle from the nanosecond to the second timescale changes as a function of the surface temperature of the particle and discuss the model of a frequency dependent effective temperature of hot Brownian motion.