Screening in (d+s)-wave superconductors: Application to Raman scattering

Schnyder, Andreas P.; Mudry, Christopher; Manske, Dirk

Screening in (d+s)-wave superconductors: Application to Raman scattering

Authors

Schnyder, Andreas P.

Mudry, Christopher

Manske, Dirk

Description

We study the polarization-dependent electronic Raman response of untwinned YBa$_2$Cu$_3$O$_{7-δ}$ superconductors employing a tight-binding band structure with anisotropic hopping matrix parameters and a superconducting gap with a mixing of $d$- and s-wave symmetry. Using general arguments we find screening terms in the $B^{\}_{1g}$ scattering channel which are required by gauge invariance. As a result, we obtain a small but measurable softening of the pair-breaking peak, whose position has been attributed for a long time to twice the superconducting gap maximum. Furthermore, we predict superconductivity-induced changes in the phonon line shapes that could provide a way to detect the isotropic s-wave admixture to the superconducting gap.
typos corrected, 6 pages, 3 figures