Magnetoelectric effect in topological insulators

Topological insulators are quite novel in several aspects. Strong spin-orbit coupling is responsible for inversion of band structure in these materials. And the junction of topological insulator and usual (nontopological) insulators show quantum spin Hall effect (QSHE), one aspect of which the topological magnetoelectric effect.

Study of electrodynamics shows such effects arise due to coupling of electric and magnetic field in the Lagrangian density function and as a consequence in the action as well. The coupling term brings about corrections in Maxwell's equations as well, which now has coupling between electric and magnetic field even in steady condition! The classic image problem (with insulator) will have magnetic field of a magnetic monopole! A dielectric slab will develop magnetic field between capacitor plates! Light rays will show Faraday and Kerr rotations!