LARGE-POLARON EFFECTS IN THE INFRARED-SPECTRUM OF HIGH-T-C CUPRATE SUPERCONDUCTORS

The infrared absorption spectra of high-T-c cuprate superconductors ar e examined in the framework of the theory for the optical absorption o f single large polarons. The experimental so-called ''anomalous Drude' ' contribution to the optical absorption exhibits similarities, both i n lineshape and in temperature dependence, to the low-frequency to (om ega < omega(LO phonon)) theoretical large polaron absorption spectrum. The polaron spectrum at omega > omega(LO phonon) has a similar temper ature and frequency dependence as the experimentally observed absorpti on band around 1000 cm(-1) (denoted as the ''d-band''). We present com parisons 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 sing le fitting material parameter. (C) 1998 Elsevier Science Ltd. All righ ts reserved.