On the Inner Topological Pressure within the Topological Insulators

Topological insulators (TIs) have axion electrodynamics instead of the usual Maxwell. Then, there is an additional energy density, whose origin is topological, generating a pressure that is found analytically. It is shown that the topological electric and magnetic fields act only on the surface, while the scalar axion does as a real Klein-Gordon field in all the TI, giving rise to a behavior quite similar to the Casimir effect without the intervention of the virtual photons of the vacuum. This opens the possibility to experimentally test the electrodynamics of axions for the TIs.