Optical Conductivity of Clean Metals
  We briefly review some basic aspects of transport in clean metals focusing on the role of electron-electron interactions and neglecting the effects of impurities, phonons and interband transitions. Both for small Fermi surfaces of two and three-dimensional metals and open Fermi surfaces of quasi one-dimensional metals the dc conductivity sigma is largely dominated by momentum and pseudo-momentum conservation, respectively. In general, the frequency and temperature dependencies of sigma(w,T) have very little in common. For small Fermi surfaces in three dimensions we find for example that the scattering rate is quadratic in frequency, Gamma \propto w^2, even in the absence of a T^2 contribution. 
A. Rosch