Electronic Raman scattering in superconductors as a probe of anisotropic electron pairing
Abstract
A gauge invariant theory for electronic Raman scattering for superconductors with anisotropic pairing symmetry is analyzed in detail. It is shown that Raman scattering in anisotropic superconductors provides a wealth of polarization-dependent information which probes the detailed angular dependence of the superconducting ground state order parameter. The Raman spectra shows a unique polarization dependence for various anisotropic pair- state symmetries which affects the peak position of the spectra and generates symmetry dependent low frequency and temperature power-laws which can be used to uniquely identify the magnitude and symmetry of the energy gap. In particular, we calculate the collective modes and the subsequent symmetry--dependent Raman spectra for a
d
x
2
−
y
2
superconductor and compare our results to the relevant data on the cuprate systems as well as theoretical predictions for
s
--wave, anisotropic
s
--wave and
s+id
energy gaps. Favorable agreement is shown with the predictions for
d
x
2
−
y
2
pairing and the experimental data on YBa
2
Cu
3
O
7
, Bi
2
Sr
2
CaCu
2
O
8
and Tl
2
Ba
2
CuO
6
.