Negative Casimir Entropies in Nanoparticle Interactions

TL;DR

This paper investigates the occurrence of negative Casimir entropy in nanoparticle interactions, revealing that negative entropy can arise from geometric and material anisotropies in small-scale systems.

Contribution

It demonstrates that negative Casimir entropy can occur in various nanoparticle configurations, including anisotropic and material-specific cases, expanding understanding beyond traditional parallel plate models.

Findings

Negative entropy occurs in nanoparticle interactions with specific anisotropies.

Negative entropy can be observed between conducting spheres and plates.

Various configurations exhibit negative entropy, including anisotropic and material-dependent cases.

Abstract

Negative entropy has been known in Casimir systems for some time. For example, it can occur between parallel metallic plates modeled by a realistic Drude permittivity. Less well known is that negative entropy can occur purely geometrically, say between a perfectly conducting sphere and a conducting plate. The latter effect is most pronounced in the dipole approximation, which is reliable when the size of the sphere is small compared to the separation between the sphere and the plate. Therefore, here we examine cases where negative entropy can occur between two electrically and magnetically polarizable nanoparticles or atoms, which need not be isotropic, and between such a small object and a conducting plate. Negative entropy can occur even between two perfectly conducting spheres, between two electrically polarizable nano-particles if there is sufficient anisotropy, between a perfectly conducting sphere and a Drude sphere,and between a sufficiently anisotropic electrically polarizable nano-particle and a transverse magnetic conducting plate.