Infrared Active Vibrational Modes Strongly Coupled to Carriers in High- T c Superconductors

Abstract
Infrared active vibrational modes (IRAV), similar to the extra-phonon absorption features which are likely to be responsible for polaron formation in insulating cuprates, have been detected in a metallic Bi2Sr2CuO6 film. The new modes can also be identified in the spectra of superconducting Nd2 - xCexCuO4 - y and YBa2Cu3O7 - y. A comparison with tunnelling results confirms that such IRAV are strongly coupled to the charge carriers.