Large-polaron effects in the infrared spectrum of high-Tc cuprate superconductors

The infrared absorption spectra of high-T-c cuprate superconductors are examined in the framework of the theory for the optical absorption of single large polarons. The experimental so-called "anomalous Drude" contribution to the optical absorption exhibits similarities, both in lineshape and in temperature dependence, to the low-frequency to (omega < omega(LO phonon)) theoretical large polaron absorption spectrum. The polaron spectrum at omega > omega(LO phonon) has a similar temperature and frequency dependence as the experimentally observed absorption band around 1000 cm(-1) (denoted as the "d-band"). We present comparisons between theory and experiment for specific cuprate materials, namely Bi2Sr2CaCu2O8 and YBa2Cu3O7 using as input for the theoretical calculations the experimental phonon frequencies together with a single fitting material parameter. (C) 1998 Elsevier Science Ltd. All rights reserved.