Dependence of the excitation wavelength on the Raman-active phonons of YBa 2Cu 3O 7: Search for Landau damping in single-domain crystals

Abstract

In single-domain crystals of YBa 2Cu 3O 7, we examine the dependence of phonon linewidth on wavevector by varying the wavelength of the exciting laser. In three crystals, we find the linewidths of the Raman-active phonons at 120 and 150 cm −1 to be nearly invariant for excitation wavelengths between 647 and 413 nm. That is, we find no broadening of the phonon linewidths with increasing phonon wavevector (decreasing excitation wavelength), and thus no evidence of Landau damping in our crystals. In addition, the correlation between the intensity of the chain-related Raman feature at ≈232 cm −1 and the temperature dependence of the B 1g-like phonon at 340 cm −1 has been investigated. In all three crystals, we find a net sharpening of the 340 cm −1 phonon below T c and essentially no intensity for the ≈232 cm −1 mode under resonance conditions.