Multi-symmetry and Multi-band Superconductivity in Filled-skutterudites PrOs$_4$Sb$_{12}$ and PrRu$_4$Sb$_{12}$

TL;DR

This study investigates the superconducting gap structures of PrOs$_4$Sb$_{12}$ and PrRu$_4$Sb$_{12}$ using thermal conductivity, revealing nodal gaps in PrOs$_4$Sb$_{12}$ and fully gapped behavior in PrRu$_4$Sb$_{12}$, with evidence of multi-band effects.

Contribution

The paper provides experimental evidence for multi-symmetry and multi-band superconductivity in filled skutterudites through thermal conductivity measurements.

Findings

PrRu$_4$Sb$_{12}$ exhibits fully gapped superconductivity.

PrOs$_4$Sb$_{12}$ shows evidence of nodal gaps.

Both compounds display multi-band effects in their superconducting states.

Abstract

Thermal conductivity measurements were performed on single crystal samples of the superconducting filled skutterudite compounds PrOs$_4$Sb$_{12}$ and PrRu$_4$Sb$_{12}$ both as a function of temperature and magnetic field applied perpendicular to the heat current. In zero magnetic field, the low temperature electronic thermal conductivity of PrRu$_4$Sb$_{12}$ is vanishingly small, consistent with a fully-gapped Fermi surface. For PrOs$_4$Sb$_{12}$, however, we find clear evidence for residual electronic conduction as the temperature tends to zero Kelvin which is consistent with the presence of nodes in the superconducting energy gap. The field dependence of the electronic conductivity for both compounds shows a rapid rise immediately above H$_{c1}$ and significant structure over the entire vortex state. In the fully gapped superconductor PrRu$_4$Sb$_{12}$, this is interpreted in terms of multi-band effects. In PrOs$_4$Sb$_{12}$, we consider the Doppler shift of nodal quasiparticles at low fields and multiband effects at higher fields.