BACK-FLOW ELECTRIC-CURRENT - DC CURRENT AS A QUADRATIC RESPONSE TO ANAC FIELD

We study the interaction of a running longitudinal wave with a metal. It is shown within a quadratic response that a single wave creates a d e electric current even if the creation of electron-hole pairs is proh ibited. As a consequence, a macroscopic electric current depends on an instant distribution of bosons, e.g., plasmons. Beside a formal theor y, two practical formulas are provided: the random phase approximation formula for a general electron band structure and a general formula f or a single parabolic band.