Structural anisotropy and orientation-induced Casimir repulsion in fluids

Abstract

In this work we theoretically consider the Casimir force between two periodic arrays of nanowires (both in vacuum, and on a substrate separated by a fluid) at separations comparable to the period. Specifically, we compute the dependence of the exact Casimir force between the arrays under both lateral translations and rotations. Although typically the force between such structures is well characterized by the proximity force approximation (PFA), we find that in the present case the microstructure modulates the force in a way qualitatively inconsistent with PFA. We find instead that effective-medium theory, in which the slabs are treated as homogeneous, anisotropic dielectrics, gives a surprisingly accurate picture of the force, down to separations of half the period. This includes a situation for identical, fluid-separated slabs in which the exact force changes sign with the orientation of the wire arrays, whereas PFA predicts attraction. We discuss the possibility of detecting these effects in experiments, concluding that this effect is strong enough to make detection possible in the near future.

Influence of hBN orientation on the near-field radiative heat transfer between graphene/hBN heterostructures

“…This technique has been used by Rosa et al 44,45 in their analysis of the Casimir interactions for anisotropic magnetodielectric metamaterials. If the incident wave is TM wave, the EM fields in the medium can be written with reference to the x 0 y 0 z 0 coordinate system as the following form: 44 E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 1 5 ; 1 1 6 ; 3 2 7 H ¼ UðzÞ expðjωt − jβxÞ; where U ¼ ðU x ; U y ; U z Þ;…”

Quantum vacuum photon modes and repulsive Lifshitz–van der Waals interactions

“…The use of the EMA has to be justified with great care. Indeed, such an approximation usually requires the separation distance L to be equal or larger than the lattice parameter a 0 of the periodically nanostructured surface [14]. The reason is that the distance is one of the main parameter determining the nature of the electromagnetic modes (radiative or evanescent) involved in the calculation of the Lifshitz-van der Waals interaction.…”

“…In this case, the assimilation of the surface corrugation to a graded effective refractive index layer is relevant [11][12][13] and allows simplifying greatly the application of nonadditive methods, while still taking fully into account electrodynamical coupling between features as it will be explained below. Motivated by recent theoretical [13][14][15] and experimental [16] studies, we introduce the novel concept of manipulating quantum vacuum photon modes at the sub-10nm scale in order to turn Lifshitz-van der Waals interactions from attractive to repulsive.…”

Casimir repulsion in sphere-plate geometry

“…At the same time the metallic bodies with more sophisticated shape were studied, and for certain cases Casimir repulsion due to the geometry was predicted in [15]. The repulsion for fluid-separated sphere and plate with ε sph (iξ) < ε f luid (iξ) < ε plate (iξ) was considered in [16,17].…”