We investigate the hole and lattice dynamics in a prototypical high-temperature superconducting system ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ using infrared spectroscopy. By exploring the anisotropy in the electronic response of $\mathrm{Cu}{\mathrm{O}}_2$ planes we show that our results support the notion of stripes. Nevertheless, charge ordering effects are not apparent in the phonon spectra. All crystals show only the expected infrared active modes for orthorhombic phases without evidence for additional peaks that may be indicative of static charge ordering. Strong electron-phonon interaction manifests itself through the Fano line shape of several phonon modes. This analysis reveals anisotropic electron-phonon coupling across the phase diagram, including superconducting crystals. Due to the ubiquity of the $\mathrm{Cu}{\mathrm{O}}_2$ plane, these results may have implications for other high temperature superconductors.

• Received 18 May 2005

DOI:https://doi.org/10.1103/PhysRevB.72.205101