Umrath Stefan, Hartmann Michael, Ingold Gert-Ludwig, Neto Paulo A Maia
Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86135 Augsburg, Germany.
Instituto de Física, UFRJ, CP 68528, Rio de Janeiro RJ 21941-909, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Oct;92(4):042125. doi: 10.1103/PhysRevE.92.042125. Epub 2015 Oct 12.
Dissipative electromagnetic response and scattering geometry are potential sources for the appearance of a negative Casimir entropy. We show that the dissipative contribution familiar from the plane-plane geometry appears also in the plane-sphere and the sphere-sphere geometries and adds to the negative Casimir entropy known to exist in these geometries even for perfectly reflecting objects. Taking the sphere-sphere geometry as an example, we carry out a scattering-channel analysis, which allows us to distinguish between the contributions of different polarizations. We demonstrate that dissipation and geometry share a common feature making possible negative values of the Casimir entropy. In both cases there exists a scattering channel whose contribution to the Casimir free energy vanishes in the high-temperature limit. While the mode-mixing channel is associated with the geometric origin, the transverse electric channel is associated with the dissipative origin of the negative Casimir entropy. By going beyond the Rayleigh limit, we find even for large distances that negative Casimir entropies can occur also for Drude-type metals provided the dissipation strength is sufficiently small.
耗散电磁响应和散射几何是负卡西米尔熵出现的潜在来源。我们表明，平面 - 平面几何中常见的耗散贡献也出现在平面 - 球体和球体 - 球体几何中，并且即使对于完全反射物体，也会增加已知存在于这些几何中的负卡西米尔熵。以球体 - 球体几何为例，我们进行了散射通道分析，这使我们能够区分不同极化的贡献。我们证明，耗散和几何具有一个共同特征，使得卡西米尔熵可能为负值。在这两种情况下，都存在一个散射通道，其对卡西米尔自由能的贡献在高温极限下消失。虽然模式混合通道与几何起源相关，但横向电通道与负卡西米尔熵的耗散起源相关。通过超越瑞利极限，我们发现即使对于大距离，只要耗散强度足够小，德鲁德型金属也可能出现负卡西米尔熵。
