Infrared spectra of superconducting La_2−xSr_xCuO₄and YBa₂Cu₃O_7−δ

Abstract Infrared spectra of La2−xSrxCuO4 and YBa2Cu3O7−δ are discussed, specially with respect to the disappearance of the high-frequency (∼650 cm) band of the superconducting compositions at 300K. Some of the bands persist at 300K eventhough the materials are fairly conducting. YBa2Cu3O7−δ does not show evidence in the far IR spectrum for the presence of an optical gap.