Low-temperature thermal transport properties of BaNi$_2$As$_2$

Low-temperature specific heat $C$($T$) and thermal conductivity $\kappa$($T$) measurements under magnetic field have been performed on a recently discovered Ni-based superconductor BaNi$_2$As$_2$ ($T_{\mathrm{c}}$\,=\,0.7\,K). In zero field, $\kappa$($T$) shows $T$-linear behavior in the normal state and exhibits a BCS-like exponential decrease below $T_{\mathrm{c}}$. The field dependence of the residual thermal conductivity extrapolated to zero temperature is indicative of a fully gapped superconductor. This conclusion is supported by the analysis of $C$($T$) data, which are well fit based on the BCS theory.