Low-temperature magneto-thermal transport investigation of a Ni-based superconductor BaNi2As2: Evidence for fully gapped superconductivity

We have performed low-temperature specific heat and thermal conductivity measurements of the Ni-based superconductor BaNi${}_2$As${}_2$ ($T_{\mathrm{c}}$ = 0.7 K) in magnetic field. In zero field, thermal conductivity 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 the specific heat data, which are well fit by the BCS temperature dependence from $T_{\mathrm{c}}$ down to the lowest temperature of 0.1 K.