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Quasiparticle-Self-Energy and its Effect on the Superconducting Order Parameter of the Pyrochlore Superconductor Cd2Re2O7

The magnitude and the temperature dependence of the superconducting order parameter Δ(T) of single-crystals of Cd2Re2O7 (Tc = 1.02 K) was measured using point contact spectroscopy. In order to fit the conductance spectra and to extract the order parameter at different temperatures we generalized the Blonder-Tinkham-Klapwijk theory by including the self-energy of the quasiparticles into the Bogoliubov equations. This modification enabled excellent fits of the conductance spectra. Δ(T) increases steeply below the superconducting transition temperature of 1.02 K and levels off below about 0.8 K depending on measurement directions where its value varied from 0.22(1) meV to 0.26(1) meV. Our results indicate the presence of a strong electron-phonon interaction and an enhanced quasiparticle damping and may be related to a possible phase transition within the superconducting region at about 0.8 K.