Fully gapped superconductivity in Ni-pnictide superconductors BaNi2As2 and SrNi2P2

TL;DR

This study demonstrates that Ni-pnictide superconductors BaNi2As2 and SrNi2P2 exhibit fully gapped s-wave superconductivity, with experimental evidence ruling out nodes on the Fermi surfaces, suggesting universality among Ni-pnictides.

Contribution

The paper provides experimental evidence of fully gapped superconductivity in Ni-pnictides, expanding understanding of their pairing symmetry and suggesting it may be a universal feature.

Findings

Both compounds show s-wave-like temperature dependence of specific heat and thermal conductivity.

Residual thermal conductivity responses indicate absence of nodes on Fermi surfaces.

Doping with La mildly suppresses T_c and H_c2 in BaNi2As2.

Abstract

We have performed low-temperature specific heat $C$ and thermal conductivity $\kappa$ measurements on the Ni-pnictide superconductors BaNi$_2$As$_2$ ($T_\mathrm{c}$=0.7 K and SrNi$_2$P$_2$ ($T_\mathrm{c}$=1.4 K). The temperature dependences $C(T)$ and $\kappa(T)$ of the two compounds are similar to the results of a number of s-wave superconductors. Furthermore, the concave field responses of the residual $\kappa$ for BaNi$_2$As$_2$ rules out the presence of nodes on the Fermi surfaces. We postulate that fully gapped superconductivity could be universal for Ni-pnictide superconductors. Specific heat data on Ba$_{0.6}$La$_{0.4}$Ni$_2$As$_2$ shows a mild suppression of $T_\mathrm{c}$ and $H_\mathrm{c2}$ relative to BaNi$_2$As$_2$.