Phase-space approach to polaron response: Kadanoff and FHIP re-examined

Abstract

A method is presented to obtain the linear response coefficients of a system coupled to a bath. The method is based on a systematic truncation of the Liouville equation for the reduced distribution function. The first order truncation results are expected to be accurate in the low temperature and weak coupling regime. Explicit expressions for the conductivity of the Fr\"ohlich polaron are obtained, and the discrepancy between the Kadanoff and the Feynman-Hellwarth-Iddings-Platzmann mobility is elucidated.