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Phonon anomalies and electron-phonon interaction in RuSr_2GdCu_2O_8 ferromagnetic superconductor: Evidence from infrared conductivity

A. V. Boris·P. Mandal·C. Bernhard·N. N. Kovaleva·K. Pucher·J. Hemberger·A. Loidl
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Abstract

Critical behavior of the infrared reflectivity of RuSr_2GdCu_2O_8 ceramics is observed near the superconducting T_{SC} = 45 K and magnetic T_M = 133 K transition temperatures. The optical conductivity reveals the typical features of the c-axis optical conductivity of strongly underdoped multilayer superconducting 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_{SC} is clearly observed, and is accompanied by the suppression of spectral weight 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 evidence 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. The underdoped character of the superconductor is explained by strong hole depletion of the CuO_2 planes caused by the charge carrier self-trapping at the Ru moments.

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A. V. Boris, P. Mandal, C. Bernhard, N. N. Kovaleva, K. Pucher, J. Hemberger, A. Loidl. 2000-12-29. Phonon anomalies and electron-phonon interaction in RuSr_2GdCu_2O_8 ferromagnetic superconductor: Evidence from infrared conductivity. https://doi.org/10.1103/physrevb.63.184505

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