Quasitopological electromagnetic response of line-node semimetals

Topological semimetals are gapless states of matter which have robust surface states and characteristic electromagnetic responses. In this paper, we consider the electromagnetic response of gapless phases in 3 + 1 dimensions with line nodes. We show through a layering approach that an intrinsic antisymmetric tensor B-mu nu. (2-form), which is determined by the geometry and energy-embedding of the nodal lines, emerges in the effective response field theory. B-mu nu is shown to be simply related to the charge polarization and orbital magnetization of the sample; hence the geometry of the line nodes determines these electromagnetic observables. We conclude by discussing the relevance for recently proposed materials and heterostructures with line-node fermi-surfaces.