  We study a class of defect quantum field theories where the quantum field
theory in the 3+1-dimensional bulk is a free photon and charged matter and the
interactions of the photons with the charges occur entirely on a
2+1-dimensional defect. We observe that at the fully quantum level, the
effective action of such a theory is still a defect field theory with free
photons propagating in the bulk and the nonlinearities in the quantum
corrections to the Maxwell equations confined to the defect. We use this
observation to show that the defect field theory has interesting
electromagnetic properties. The electromagnetic fields sourced by static test
charges are attenuated as if the bulk surrounding them were filled with a
dielectric material. This is particularly interesting when the observer and
test charge are on opposite sides of the defect. Then the effect is isotropic
and it is operative even in the region near the defect. If the defect is in a
time reversal violating state, image charges have the appearance of
electrically and magnetically charged dyons. We present the example of a single
layer in a quantum Hall state. We observe that the charge screening effect in
charge neutral graphene should be significant, and even more dramatic when the
layer is in a metallic state with mobile electrons.
