Non-equilibrium properties of an active nanoparticle in a harmonic potential

Active particles break out of thermodynamic equilibrium thanks to their directed motion, which leads to complex and interesting behaviors in the presence of confining potentials. When dealing with active nanoparticles, however, the overwhelming presence of rotational diffusion hinders directed motio...

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Bibliographic Details
Published in:Nature communications 2021-03, Vol.12 (1), p.1902-1902, Article 1902
Main Authors: Schmidt, Falko, Šípová-Jungová, Hana, Käll, Mikael, Würger, Alois, Volpe, Giovanni
Format: Article
Language:English
Subjects:
639/766/400/1021
639/766/530/2803
639/925
Boltzmann distribution
Condensed Matter
Critical point
Crossovers
Equilibrium
Fokker-Planck equation
Fysik
Humanities and Social Sciences
multidisciplinary
Nanoparticles
Nanospheres
Physical Sciences
Physics
Rotational diffusion
Science
Science (multidisciplinary)
Thermodynamic equilibrium
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Summary:Active particles break out of thermodynamic equilibrium thanks to their directed motion, which leads to complex and interesting behaviors in the presence of confining potentials. When dealing with active nanoparticles, however, the overwhelming presence of rotational diffusion hinders directed motion, leading to an increase of their effective temperature, but otherwise masking the effects of self-propulsion. Here, we demonstrate an experimental system where an active nanoparticle immersed in a critical solution and held in an optical harmonic potential features far-from-equilibrium behavior beyond an increase of its effective temperature. When increasing the laser power, we observe a cross-over from a Boltzmann distribution to a non-equilibrium state, where the particle performs fast orbital rotations about the beam axis. These findings are rationalized by solving the Fokker-Planck equation for the particle’s position and orientation in terms of a moment expansion. The proposed self-propulsion mechanism results from the particle’s non-sphericity and the lower critical point of the solution. For active particles with nanoscale dimensions the overwhelming rotational diffusivity usually masks their residual non-equilibrium character. Here Schmidt et al. show how to amplify it in a suitable experiment to let a nanosphere rotate spontaneously around the beam axis in an optical trap.
ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-021-22187-z