Complex poles and oscillatory screened potential in QED plasmas

We discuss the mechanism for the oscillatory behavior of the static interparticle potential in a degenerate electron plasma. This behavior, observed in metallic alloys, is commonly referred to as 'Friedel oscillations', and its origin associated to the Kohn singularity. We show that, although this interpretation is adequate for large distances, the oscillations at short distances originate from a complex pole of the in-medium photon propagator in the complex q-plane, which exists aside the (purely imaginary) Debye pole. Such short-range oscillations can be physically discriminated if they remain at temperatures for which Friedel oscillations have already disappeared. This is suggested by finite temperature calculations in non-electromagnetic plasma models showing a similar pole structure.