We report the ${}^{207}\mathrm{Pb}$ nuclear magnetic resonance (NMR) measurements on polycrystalline sample of ${\mathrm{PbTaSe}}_2$ with noncentrosymmetric crystal structure and topological electronic band. The nuclear spin-lattice relaxation rate $1/T_1$ shows a suppressed coherence peak below the superconducting transition temperature $T_{\mathrm{c}}=4.05\mathrm{K}$ and decreases as an exponential function of temperature. The penetration depth derived from the NMR spectrum is almost temperature independent below $T=0.7$ $T_{\mathrm{c}}$. The Knight shift $K$ decreases below $T_{\mathrm{c}}$. These results suggest spin-singlet superconductivity with a fully opened gap $2\mathrm{\Delta }=3.5k_{\mathrm{B}}{T}_{\mathrm{c}}$ in ${\mathrm{PbTaSe}}_2$.

• Received 20 April 2018

DOI:https://doi.org/10.1103/PhysRevB.97.184510