Incoherent optical conductivity and breakdown of the generalized Drude formula in quasi-one-dimensional bad metallic systems

Abstract

The high-energy (HE) intraband optical processes in a wide class of strongly correlated quasi-one-dimensional systems are explained in a way that is consistent with the Fermi golden rule, by using the force-force correlation function (FFCF) theory. It turns out that these processes must be distinguished from the related low-energy (LE) optical processes of the generalized Drude formula by making use of two different summations of Feynman diagrams, which include, respectively, the large-momentum and $\mathbf{q}\ensuremath{\approx}0$ electron-hole excitations. Using the FFCF approach, the common expression for the single-particle optical conductivity of clean charge-density-wave (CDW) systems is rederived and the formation of the CDW gap in the optical conductivity of dirty CDW systems is briefly discussed. It is argued that the clear distinction between the HE and LE intraband optical processes is required whenever the electrical/optical conductivity of conduction electrons is predominantly incoherent, including the cases of bad metallic compounds and various heavy-electron systems.