Electronic Raman scattering in unconventional density waves

Abstract

We investigate the electronic Raman scattering in pure, quasi-one-dimensional conductors with a density wave ground state. In particular, we develop the theory of light scattering on spin and charge density waves, both conventional and unconventional. We calculate the electronic Raman response of the interacting-electron system with a single, highly anisotropic conduction band. The calculation is carried out in the mean-field approximation. In addition to the quasiparticle contribution, the electron-electron interaction is also included on the level of the random phase approximation. The contribution of collective modes and the effect of Coulomb screening are investigated. In analogy with unconventional superconductivity, the obtained Raman spectra---which are finite in the low-temperature phase possessing a gap, and vanish identically in the normal state---show unique and strong dependence on the polarization of the incoming and scattered light. We have found distinct, characteristic line shapes, especially in the unconventional situation, depending on the various scattering geometries and the particular momentum dependence of the density wave order parameter.