Kohn's Theorem and Correlation Functions for a Fermi Liquid

Abstract

In this paper we derive Kohn's theorem and calculate the spin and current response functions for a Fermi liquid. A magnetic weight is introduced as the limit $\omega /q\to 0$ of the spin response function in analogy to the superfluid weight recently introduced by Scalapino and collaborators. It is conjectured that in this limit both the magnetic-ordered and the Fermi-liquid spin response functions have the same value.