Oxygen phonon branches in overdoped La 1.7 Sr 0.3 Cu 3 O 4

The dispersion of $\mathrm{Cu}\char21{}\mathrm{O}$ bond-stretching vibrations in overdoped ${\mathrm{La}}_{1.7}{\mathrm{Sr}}_{0.3}{\mathrm{CuO}}_{4}$ (not superconducting) has been studied by high-resolution inelastic neutron scattering. It was found that the doping-induced renormalization of the so-called breathing and half-breathing modes is larger than in optimally doped ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}$. On the other hand, the phonon linewidths are generally smaller in the overdoped sample. Features observed in optimally doped ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}$ which suggest a tendency towards charge stripe formation are absent in overdoped ${\mathrm{La}}_{1.7}{\mathrm{Sr}}_{0.3}{\mathrm{CuO}}_{4}$.