Phonon anomalies and electron-phonon interaction in the RuSr2GdCu2O8 ferromagnetic superconductor: Evidence from infrared conductivity - art. no. 184505

Critical behavior of the infrared reflectivity of RuSr2GdCu2O8 ceramics is observed near the superconducting T-SC = 45 K and magnetic T-M = 133 K tran sition temperatures. The optical conductivity reveals the typical features of the c-axis optical conductivity of strongly underdoped multilayer superc onducting cuprates. The transformation of the Cu-O bending mode at 288 cm(- 1) to a broad absorption peak at the temperatures between T* = 90 K and T-S C is clearly observed, and is accompanied by the suppression of spectral we ight at low frequencies. The correlated shifts to lower frequencies of the Ru-related phonon mode at 190 cm(-1) and the mid-IR band at 4800 cm(-1) on decreasing temperature below T-M are observed. It provides experimental evi dence in favor of strong electron-phonon coupling of the charge carriers in the Ru-O layers which critically depends on the Ru core spin alignment. Th e underdoped character of the superconductor is explained by strong hole de pletion of the CuO2 planes caused by the charge carrier self-trapping at th e Ru moments.