  The response to an electric field (DC and AC) of electronic systems in which
the Fermi "surface" consists of a number of 3D Weyl points (such as some
pyrochlore iridates) exhibits a peculiar combination of characteristics usually
associated with insulating and conducting behaviour. Generically a neutral
plasma in clean materials can be described by a tight binding model with a
strong spin-orbit interaction. A system of that type has a vanishing DC
conductivity; however the current response to the DC field is very slow: the
current decays with time in a powerwise manner, different from an insulator.
The AC conductivity, in addition to a finite real part which is linear in
frequency, exhibits an imaginary part that increases logarithmically as
function of the UV cutoff (atomic scale). This leads to substantial dielectric
response like a large dielectric constant at low frequencies. This is in
contrast to a 2D Weyl semimetal like graphene at neutrality point where the AC
conductivity is purely pseudo-dissipative. The Coulomb interaction between
electrons is long range and sufficiently strong to make a significant impact on
transport. The interaction contribution to the AC conductivity is calculated
within the tight binding model.
