Geometric origin of negative Casimir entropies: A scattering-channel analysis

Abstract

Negative values of the Casimir entropy occur quite frequently at low temperatures in arrangements of metallic objects. The physical reason lies either in the dissipative nature of the metals as is the case for the plane-plane geometry or in the geometric form of the objects involved. Examples for the latter are the sphere-plane and the sphere-sphere geometry, where negative Casimir entropies can occur already for perfect metal objects. After appropriately scaling out the size of the objects, negative Casimir entropies of geometric origin are particularly pronounced in the limit of large distances between the objects. We analyze this limit in terms of the different scattering channels and demonstrate how the negativity of the Casimir entropy is related to the polarization mixing arising in the scattering process. If all involved objects have a finite zero-frequency conductivity, the channels involving transverse electric modes are suppressed and the Casimir entropy within the large-distance limit is found to be positive.

11 pages, 8 figures

References in corpus (5)

• Casimir Force and In Situ Surface Potential Measurements on Nanomembranes
• Lifshitz theory of atom-wall interaction with applications to quantum reflection
• On the Casimir entropy for a ball in front of a plane
• Geothermal Casimir phenomena for the sphere-plate and cylinder-plate configurations
• Derivation of the Lifshitz-Matsubara sum formula for the Casimir pressure between metallic plane mirrors

Cited by in corpus (6)

• Casimir Self-Entropy of a Spherical Electromagnetic $\delta$-Function Shell
• Casimir Self-Entropy of an Electromagnetic Thin Sheet
• Universal Casimir interactions in the sphere-sphere geometry
• Switching the sign of the Casimir force between two PEMC spheres
• Negativity of the Casimir self-entropy in spherical geometries
• Casimir Self-Entropy of Nanoparticles with Classical Polarizabilities: Electromagnetic Field Fluctuations