Temperature dependence of doping-induced modes in Cu-O planes

Measurements of the frequency-dependent conductivity confirm that unusual lattice vibrational modes are induced by doping of several materials containing Cu-O planes. We find that the modes broaden rapidly with increasing temperature, consistent with the presence of a large linear component. This broadening of these vibrational modes is similar to that of electronic modes found previously in these same materials and analyzed in attempts to understand high-temperature superconductivity.