Hamburg 2001 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 5: Fachsymposium 1: Unkonventionelle Supraleitung

TT 5.10: Vortrag

Montag, 26. März 2001, 17:30–17:45, A

Phonon anomalies in the RuSr₂GdCu₂O₈ ferromagnetic superconductor. — •Alexander Boris^1,2, Christian Bernhard¹, Nataly Kovaleva², Alois Loidl³, Joachim Hemberger³, Klaus Pucher³, and Prabhat Mandal^3,4 — ¹Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany — ²Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow district 142432 — ³Experimentalphysik V, EKM, Universität Augsburg, D-86135 Augsburg, Germany — ⁴Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Calcutta 700 064, India

FS1: Unkonventionelle Supraleiter

Critical behavior of the infrared reflectivity of RuSr₂GdCu₂O₈ ceramics is observed near the superconducting T_SC = 45 K and magnetic T_M = 133 K transition temperatures. 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 190⁻¹ and the mid-IR band at 4800⁻¹ 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 CuO₂ planes caused by the charge carrier self-trapping at the Ru moments.