Temperature dependence of the magnetic Casimir-Polder interaction

TL;DR

This paper investigates the temperature-dependent magnetic Casimir-Polder forces between atoms and surfaces, revealing significant suppression at finite temperatures and notable effects near superconducting transitions, with implications for understanding dispersion forces.

Contribution

It provides a detailed analysis of the magnetic dipole contribution to atom-surface forces, highlighting temperature effects and differences between normal metals and superconductors, including analytical asymptotes.

Findings

Temperature significantly suppresses the magnetic Casimir-Polder force at T > 0.

Superconducting phase transition causes discontinuous changes in interaction and entropy.

Analytical expressions for free energy and entropy asymptotes are derived.

Abstract

We analyze the magnetic dipole contribution to atom-surface dispersion forces. Unlike its electrical counterpart, it involves small transition frequencies that are comparable to thermal energy scales. A significant temperature dependence is found near surfaces with a nonzero DC conductivity, leading to a strong suppression of the dispersion force at T > 0. We use thermal response theory for the surface material and discuss both normal metals and superconductors. The asymptotes of the free energy of interaction and of the entropy are calculated analytically over a large range of distances. Near a superconductor, the onset of dissipation at the phase transition strongly changes the interaction, including a discontinuous entropy. We discuss the similarities with the Casimir interaction beween two surfaces and suggest that precision measurements of the atom-surface interaction may shed new light upon open questions around the temperature dependence of dispersion forces between lossy media.