INFRARED PROPERTIES OF METALLIC AND INSULATING LA1-ZXZCU1-XMNXO3-DELTA COMPOUNDS (X=SR, BA)

The mixed crystal series La1-zXzCu1-xMnxO3-delta with X = Sr, Ba inclu de high- T(c) superconductors, ferromagnetic (double exchange coupled) metals as well as spin-glass-like semiconductors, and therefore are s elected for comparative studies of their infrared spectra. Optical con ductivity is obtained between 150 and 4000 cm-1 through Kramers-Kronig analysis of infrared and optical reflectivity data. The information o n energy dependent interactions between electrons and other quasiparti cles or elementary excitations are provided through the analysis invol ving extended Drude and polaron transport models. Distinctive frequenc y dependent electron-phonon coupling is found in all cases which manif ests itself through the appearance of different current carrying quasi -particles. Also, two or three prominent optical phonons are observed which are not completely screened even in the normal state of the high -T(c) superconductors and do not change their positions appreciably wi thin each series. Line narrowing is suggested to occur when the magnet ic long-range order is switched on.