Abstract
We performed a detailed investigation of the superconducting properties of polycrystalline Pr1−xCexPt4Ge12 pellets. We report the effect of Ce substitution, for x = 0.07, on magnetic field phase diagram H-T. We demonstrate that the upper critical field is well described by the Ginzburg–Landau model and that the irreversibility field line has a scaling behaviour similar to cuprates. We also show that for magnetic fields lower than 0.4 T, the activation energy follows a power law of the type 𝐻−1/2, suggesting a collective pinning regime with a quasi-2D character for the Ce-doped compound with x = 0.07. Furthermore, by means of a point contact Andreev reflection spectroscopy setup, we formed metal/superconductor nano-junctions as small as tens of nanometers on the PrPt4Ge12 parent compound (x = 0). Experimental results showed a wide variety of conductance features appearing in the dI/dV vs. V spectra, all explained in terms of a modified Blonder–Tinkham–Klapwijk model considering a superconducting order parameter with nodal directions as well as sign change in the momentum space for the sample with x = 0. The numerical simulations of the conductance spectra also demonstrate that s-wave pairing and anisotropic s-waves are unsuitable for reproducing experimental data obtained at low temperature on the un-doped compound. Interestingly, we show that the polycrystalline nature of the superconducting PrPt4Ge12 sample can favour the formation of an inter-grain Josephson junction in series with the point contact junction in this kind of experiments.
Highlights
Filled skutterudite materials have attracted a great deal of attention for a large number of properties such as metal–insulator transitions, spin fluctuations, and heavy fermion behaviour [1,2,3,4]
We measured the conductance spectra of the point contact junction at low temperature (4.2 K) and we demonstrated that the conductance feature can be reproduced in a theoretical model that takes into account the Nanomaterials 2020, 10, 1810 symmetry of the superconducting order parameter with nodal directions and change of sign in the momentum space
The dynamic behaviour of Abrikosov vortices in type II superconductors determines the transport properties of superconducting samples
Summary
Filled skutterudite materials have attracted a great deal of attention for a large number of properties such as metal–insulator transitions, spin fluctuations, and heavy fermion behaviour [1,2,3,4]. Several compounds in the family of filled skutterudites show the phenomenon of superconductivity [5,6,7,8]. They have the chemical formula MT4X12, where M is an electropositive metal (Sr, Ba, La, Pr, Th), T is a transition metal (Fe, Os, or Ru), and X usually represents a pnictogen (Sb, As, or P). The first Pr-based superconductor to be discovered was the heavy-fermion PrOs4Sb12, with a critical temperature Tc = 1.85 K, showing intriguing properties such as a giant electronic specific heat coefficient [1]. A new Pt-based family of skutterudite, with chemical formula MPt4Ge12, was synthetized, showing superconducting properties at relatively high temperatures. Nuclear magnetic resonance experiments have given indications for conventional superconductivity in LaPt4Ge12 [11]
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