Pairing state in the rutheno-cuprate superconductor RuSr2GdCu2O8: A point contact Andreev Reflection Spectroscopy study

Abstract

The results of Point Contact Andreev Reflection Spectroscopy on polycrystalline RuSr${}_2$GdCu${}_2$O${}_8$ pellets are presented. The wide variety of the measured spectra are all explained in terms of a modified BTK model considering a \emph{d-wave} symmetry of the superconducting order parameter. Remarkably low values of the energy gap $\Delta =(2.8\pm 0.2)meV$ and of the $2\Delta /k_B{T}_c\simeq 2$ ratio are inferred. From the temperature evolution of the $dI/dV$ vs $V$ characteristics we extract a sublinear temperature dependence of the superconducting energy gap. The magnetic field dependence of the conductance spectra at low temperatures is also reported. From the $\Delta$ vs $H$ evolution, a critical magnetic field $H_{c_2}\simeq 30T$ is inferred. To properly explain the curves showing gap-like features at higher voltages, we consider the formation of a Josephson junction in series with the Point Contact junction, as a consequence of the granularity of the sample.

8 pages, 7 EPS figures. Accepted in Phys. Rev. B

References in corpus (3)

• Andreev - Saint James reflections: a probe of cuprate superconductors
• Andreev Reflection Spectroscopy in Niobium Point Contacts in Magnetic Field
• Subharmonic gap structures and Josephson effect in MgB2/Nb micro-constrictions

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• Andreev reflection in ferrimagnetic CoFe2O4/SrRuO3 spin filters
• Minimal model of point contact Andreev reflection spectroscopy of multiband superconductors