Electronic Raman scattering in unconventional density waves

Abstract

We investigate the electronic Raman scattering in pure, quasi-one dimensional conductors with 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. Beside the quasiparticle contribution, the electron-electron interaction is also included on RPA level. 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 lineshapes, especially in the unconventional situation, depending on the various scattering geometries and the particular momentum dependence of the density wave order parameter.

Temperature-induced change in the Fermi surface topology in the spin density wave phase of Sr(Fe1−xCox)2Yang1, Gallais2, Rullier‐Albenque3 et al. 2014Phys. Rev. B9350View full textAdd to dashboardCite

“…We note that for bands with equal curvature the sign would be positive. In that case one can show that there is a cancellation between the first two terms and the last term, yielding no contribution of SDW gap excitation to the Raman response 54 . There is analogy between these two opposite cases for the SDW response and coherence factors for type-I and type-II excitations in BCS theory.…”

Alternative route to charge density wave formation in multiband systems

“…In addition and more importantly, we show that the selection rules and the strong anisotropy of the electron-phonon coupling, which influences the CDW ordering, are intimately connected and just two sides of the same coin. The electronic Raman response, including the selection rules, can be derived directly from the band structure and the momentum dependences of the CDW gaps using the formalism in the work by Ványolos and Virosztek (32). The intensity of the light scattering for different polarization combinations (Raman vertices) are mainly determined by the curvature of the electronic dispersion, which is described in detail in ref.…”

Infrared and electronic Raman response of coexisting d-wave density wave and d-wave superconductivity

“…Next we study Raman scattering in B 1g symmetry. Here, the basis function coincides with the angular dependencies of the dDW and dSC order parameters, and as such with that of the full gap as well, and for this reason we suspect that this will lead to interference effects between the Raman vertex and the gaps [40,54]. Restricting our analysis to the the continuum limit as before, where λ B1g L=2 (k) = cos(2φ),…”

“…In the long wavelength limit the vertex is related to the generalized mass tensor of electrons [40,53,54]. We, however, instead of making an ansatz for its momentum dependence, which obviously depends strongly on the details of the dispersion ǫ(k), expand it as usual with the basis functions of the tetragonal point group D 4h relevant to cuprate superconductors [39,55,56]…”