In Griffiths Introduction to Electrodynamics (4th edition), when discussing the boundary conditions for a dielectric to (imperfect) conductor interface for a monochromatic plane wave, Griffith claims that,
For Ohmic conductors (J=σE) there can be no free surface current since this would require an infinite electric field at the boundary",
and, he adds (in an excerpt on pg 425) that
In Section 9.4.2 I argued that there can be no surface currents in an
ohmic conductor (with finite conductivity). But there are volume currents, extending in (roughly) to the skin depth. As the conductivity increases, they are squeezed into a thinner and thinner layer, and in the limit of a perfect conductor they become true surface currents.
Now, he doesn't ever explicitly state whether the current densities that he is referring to are induced by consequence of the EM wave penetrating into the conductor (where it decays) or if he is speaking in general. However, the fact that he says for an imperfect conductor there are volume currents extending into the conductor a distance (roughly) equal to the skin depth, makes me think that he is referring to currents which should result from the EM wave in the conductor (not a "preexisting current" which is already flowing in the conductor prior to incidence if that makes sense). Can anyone confirm or deny if I am correct or not? I know this will probably seem like a dumb question to some of you, but, I wanted to be as sure as possible that I wasn't misunderstanding anything. Thank you for your time!
To elaborate a bit more...consider a cylindrical (imperfect so E does not have to =0 on interior) conducting wire, where both circular ends are at a potential difference of V (uniform electric field in the wire). The current density should also be uniform if wire is of homogenous conductivity by ohms law and so the volume current does not only extend as far as the skin depth like Griffiths claims in the quote from my original post but exists uniformly distributed in the wire. Therefore, if Griffiths is not specifically referring to currents induced by EM wave penetration into the conductor, then I can't see how this is not paradoxical.