Casimir entropy for magnetodielectrics

TL;DR

This paper derives analytical expressions for the Casimir free energy, entropy, and pressure between magnetodielectric plates at low temperatures, analyzing the effects of dielectric and magnetic properties, including dc conductivity, on thermodynamic consistency.

Contribution

It provides new analytic formulas for Casimir thermodynamics in magnetodielectric systems, highlighting the impact of dc conductivity on the Nernst heat theorem.

Findings

Casimir entropy satisfies Nernst theorem with finite static permittivity and permeability.

Including dc conductivity leads to a nonzero entropy at zero temperature, violating Nernst.

The results have implications for experimental measurements of Casimir forces.

Abstract

We find the analytic expressions for the Casimir free energy, entropy and pressure at low temperature in the configuration of two parallel plates made of magnetodielectic material. The cases of constant and frequency-dependent dielectic permittivity and magnetic permeability of the plates are considered. Special attention is paid to the account of dc conductivity. It is shown that in the case of finite static dielectric permittivity and magnetic permeability the Nernst heat theorem for the Casimir entropy is satisfied. If the dc conductivity is taken into account, the Casimir entropy goes to a positive nonzero limit depending on the parameters of a system when the temperature vanishes, i.e., the Nernst theorem is violated. The experimental situation is also discussed.