Electronic Raman scattering of YBa2Cu3O7 using c-axis polarization: Evidence for two characteristic superconducting energies.

Abstract

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 \ensuremath{\sim}200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. 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 (\ensuremath{\sim}200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) and a-b polarization (400--500 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) are interpreted as superconducting energy gaps, then there is either a single anisotropic gap or two gaps.