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.

arXiv comment11 pages, 8 figures

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• The role of diffraction in the Casimir effect beyond the proximity force approximation
• Casimir Self-Entropy of a Spherical Electromagnetic $\delta$-Function Shell
• Advancing numerics for the Casimir effect to experimentally relevant aspect ratios
• Disentangling geometric and dissipative origins of negative Casimir entropies
• Quantum thermodynamics of overdamped modes in local and spatially dispersive materials
• 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
• Casimir Self-Entropy of Nanoparticles with Classical Polarizabilities: Electromagnetic Field Fluctuations
• Negativity of the Casimir self-entropy in spherical geometries
• Casimir interaction of arbitrarily shaped conductors
• Casimir entropy and internal energy of the objects in fluctuating scalar and electromagnetic fields