Raman scattering has been obtained with light polarized along the c axis of twin-free single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. For c-axis polarization, an electronic continuum is observed, similar to the continuum observed for polarization within the a-b plane. In the superconducting state, there is a small decrease in the intensity of the c-axis continuum at energies below ∼200 ${\mathrm{cm}}^{\mathrm{-}1}$. This change is not purely thermal in origin, since it occurs at essentially the same energy for temperatures between 4 and 65 K. This behavior differs from the large redistribution that occurs below ${\mathit{T}}_{\mathit{c}}$ in the continuum observed for polarization within the a-b plane. If the characteristic energies for c-axis polarization (∼200 ${\mathrm{cm}}^{\mathrm{-}1}$) and a-b polarization (400–500 ${\mathrm{cm}}^{\mathrm{-}1}$) are interpreted as superconducting energy gaps, then there is either a single anisotropic gap or two gaps.

• Received 14 June 1990

DOI:https://doi.org/10.1103/PhysRevB.42.9973