Andreev-reflection measurements in RuSr2GdCu2O8

We performed point-contact spectroscopy (PCS) measurements in polycrystalline RuSr2GdCu2O8 samples. The best conductance curves were obtained by using a metallic tip (Pt-Ir) pressed against the sample surface. The low-temperature conductance curves feature a zero-bias peak, suggestive of Andreev reflection at the interface between a normal metal and a d-wave superconductor. These curves can be easily fitted, in the framework of the generalized BTK model, by using pure d-wave symmetry. We were able to obtain the whole temperature dependence of the conductance curves from 4.2 K up to the critical temperature of the junction. The gap amplitude given by the fit presents an anomalous positive curvature in the whole temperature range. (c) 2005 Elsevier Ltd. All rights reserved.