Superconducting parameters of BaPt(4-x)Au(x)Ge12 filled skutterudite

TL;DR

This study investigates the superconducting properties of BaPt(4-x)Au(x)Ge12 skutterudites, revealing an s-wave gap, increasing gap-to-Tc ratio with Au content, and a transition between dirty and clean limits.

Contribution

It provides detailed measurements of superconducting parameters across different Au doping levels, highlighting how doping influences the gap and scattering regimes.

Findings

Superfluid density fits an s-wave superconducting gap

Gap-to-Tc ratio increases with Au content

Samples are between dirty and clean limits with mean free paths ~ coherence length

Abstract

We report on a study of the superconducting properties for a series of polycrystalline BaPt(4-x)Au(x)Ge12 filled skutterudite compounds for x = 0, 0.5, 0.75, and 1. Muon spin rotation (muSR) spectroscopy as well as magnetization, specific heat, and electrical resistivity measurements were performed. The magnetic penetration depth \lambda, the coherence length \xi, and the Ginzburg-Landau parameter \kappa are evaluated. The temperature dependence of the superfluid density is well described by an s-wave superconducting gap and this classical scenario is supported by the field-independent \lambda. The gap-to-Tc ratio \Delta/kTc increases with the Au content from 1.70 for x = 0 to 2.1(1) for x = 1. By combining muSR, magnetization, and specific heat data, we find that BaPt(4-x)Au(x)Ge12 compounds are in between the dirty and clean limits with mean free paths of the carriers l ~ \xi. Interestingly, resistivity data for BaPt4Ge12 indicate a much higher upper critical field, which is probably due to defects or impurities close to the surface of the crystallites.