Temperature-dependent phonon lifetime of the 428-${\mathrm{cm}}^{\mathrm{-}1}$ Raman line in ${\mathrm{La}}_2$${\mathrm{CuO}}_{4+\mathrm{y}}$

Raman measurements of the 428-${\mathrm{cm}}^{\mathrm{-}1}$ $A_{1g}$ oxygen vibrational mode in single-crystal ${\mathrm{La}}_2$ ${\mathrm{CuO}}_{4+\mathrm{y}}$ show that the linewidth of this dominant line increases by a factor of 2 from 8 to 300 K, while its line position varies by less than 1 ${\mathrm{cm}}^{\mathrm{-}1}$ over this temperature range. The variation with temperature of the linewidth of the zone-center optical phonon of frequency ${\omega }_0$ is well explained by a three-phonon scattering process involving a decay to two phonons with wave vectors k and -k and frequencies near ${\omega }_0$/2. No changes in either the linewidth or the line position was observed upon application of a magnetic field (H∥z^) up to 11 T.