On the universal optical conductivity and single-particle relaxation in   cuprates
  The origin of the universal optical conductivity form sigma(omega) ~ (1-e^(omega/T))/omega established in numerical model studies of doped antiferromagnets and consistent with experiments on cuprates near optimal doping is discussed. It is shown that such a behaviour appears quite generally when the single-particle excitations are overdamped and their relaxation follows the marginal Fermi liquid concept. Relation to recent ARPES experiments is also discussed. 
Peter Prelovsek (Institute for Materials Research, Tohoku University,   Sendai, Japan, Faculty of Mathematics and Physics, U...