Theory of interband electron Raman scattering in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$: A probe of unconventional superconductivity

In the Raman spectra measured on ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ single crystals there are continua of electronic origin. It is proposed that in addition to the intraband scattering there is an interband contribution due to the charge transfer between the bridging oxygen and the plane, which is strongly coupled to the 330-${\mathrm{cm}}^{\mathrm{-}1}$ phonon. We suggest that the entirely gapless feature of the spectra with ${\mathrm{B}}_{1\mathrm{g}}$ symmetry is a probe of nodes in the superconducting gap. The compatible d- and p-pairing states are listed.