Remarks on some problems in 1D-physics: nonlinear optics of (A–B) conjugated polymers and the role of electron-electron scattering in conducting Q1D materials with a soft phonon mode

Abstract

Abstract Nonlinear optical and conducting properties of Q1D materials are considered. The nonlinear optics of (A–B) polymers are discussed on the basis of the Hamiltonian of Rice and Mele. The unified theory of nonlinear susceptibilities on the framework of the nonequilibrium Keldysh technique is presented. It has been shown that the second harmonic generation takes place. The real and imaginary parts of the second hyperpolarizability are calculated and their frequency dependence found. Nonlinear electrical properties of Q1D metals are considered. It is shown that the conductivity mechanism is due to a new phase state, named a charge-density wave. A new transport properties' model of these materials in a high temperature phase has been proposed. It has been shown that the transport should be determined by electron-electron scattering and the interaction with a soft phonon mode in the vicinity of a structural phase transition.