Magneto-electric equivalence and emergent electrodynamics in bilayer graphene

It is a fundamental paradigm that the physical effects induced by electric fields are qualitatively different from those induced by magnetic fields. Here we show that electrons at a Dirac point in bilayer graphene experience an unusual type of electromagnetism where magnetic and electric fields are virtually equivalent: every coupling of an electron's degrees of freedom to a magnetic field is matched by an analogous coupling of the same degrees of freedom to an electric field. This counter-intuitive duality of matter-field interactions enables novel ways to create and manipulate spin and pseudo-spin polarizations in bilayer graphene via external fields and leads to the emergence of a valley-contrasting axion electrodynamics, where the traditional association of charges at rest with electric fields and charge currents with magnetic fields is reversed.