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arXiv · 2506.03064

Paramagnetism in spherically confined charged active matter

Balázs Németh·Ronojoy Adhikari
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Abstract

The celebrated theorem of Bohr and van Leeuwen guarantees that a classical charged system cannot have a magnetization in thermal equilibrium. Quantum mechanically, however, a diamagnetic response is obtained. In contrast, we show here that a classical charged active system, consisting of a motile particle confined to the surface of a sphere, has a nonzero magnetization and a paramagnetic response. We numerically sample Langevin trajectories of this system and compare with limiting analytical solutions of the Fokker-Planck equation, at small and large temperatures, to find excellent agreement in the magnetic response. Our Letter suggests experimental routes to controlling and extracting work from charged active matter.

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Balázs Németh, Ronojoy Adhikari. 2025-06-03. Paramagnetism in spherically confined charged active matter. https://doi.org/10.1103/ccv9-c322

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