Signatures of complex optical response in Casimir interactions of type I and II Weyl semimetals

Abstract

The Casimir interaction is induced by electromagnetic fluctuations between objects and it is strongly dependent upon the electronic and optical properties of the materials making up the objects.Here we investigate this ubiquitous interaction between Weyl semimetals, a class of 3D systems with low energy linear dispersion and nontrivial topology due to symmetry conditions and stemming from separated energy cones. A comprehensive examination of all components of the bulk conductivity tensor as well as the surface conductivity due to the Fermi arc states in real and imaginary frequency domains is presented using the Kubo formalism for Weyl semimetals with different degree of tilting of their linear energy cones. The Casimir energy is calculated using a generalized Lifhsitz approach, for which electromagnetic boundary conditions for anisotropic materials were derived and used. We find that the Casimir interaction between Weyl semimetals is metallic-like and its magnitude and characteristic distance dependence can be modified by the degree of tilting and chemical potential. The nontrivial topology plays a secondary role in the Casimir interaction of these 3D materials and thermal fluctuations are expected to have similar effects as in metallic systems. arXiv:1911.03377v2 [cond-mat.mtrl-sci]

How Many Surface Modes Does One See on the Boundary of a Dirac Material?

“…Another place where our results will be useful is the computations of Casimir interaction between Dirac materials (see recent papers [21][22][23][24] and references therein), which are motivated by the exciting possibility to get a repulsive Casimir force. Note, that since the Casimir force is given by a momentum integral, it is important to have expressions for the polarization tensor at all frequencies, as we gave here.…”

Perspective on Some Recent and Future Developments in Casimir Interactions

“…where b 1 , b 2 are the Dirac cone separations of the interacting materials. Since the product b 1 b 2 can be positive or negative as the cone separation can be in positive or negative momentum space domains, the Casimir interaction can be attractive or repulsive [58,59]. Note that the b-parameters, which essentially determine the axion term in the electrodynamics, are continuous.…”

Casimir force between Weyl semimetals in a chiral medium

“…This fact renders both plates rotationally symmetric, and we found that this implies that they show a particular response in presence of circularly polarized light: Each photon sees the WSM as an imperfect isotropic mirror, but with a different reflection coefficient depending on its chirality. Even if the gap is filled with vacuum, WSMs exhibit interesting features regarding Casimir interactions, as has been shown in the literature [19,22]. We found that a flipping of one sample in real space may switch the system from repulsive to attractive and vice versa, which makes WSMs very versatile materials from the point of view of investigating the Casimir force, given the fact that the same sample may exhibit either repulsion or attraction depending only on its orientation with respect to another sample.…”

“…This symmetry breaking is what allows for the existence of Casimir repulsion, and is what was exploited by Wilson et al [19], who considered a system of two identical time-reversal symmetry breaking WSMs. There is also a very recent work where these results have been extended to type-II WSMs, and include the effect of surface currents [22].…”