We report ${}^{195}\mathrm{Pt}$ nuclear magnetic resonance (NMR) measurements on topological superconductor candidate YPtBi, which has broken inversion symmetry and topological nontrivial band structures due to the strong spin-orbit coupling. In the normal state, we find that Knight shift $K$ is field- and temperature independent, suggesting that the contribution from the topological bands is very small at low temperatures. However, the spin-lattice relaxation rate $1/T_1$ divided by temperature ($T$), $1/T_{1}T$, increases with decreasing $T$, implying the existence of antiferromagnetic spin fluctuations. In the superconducting state, no Hebel-Slichter coherence peak is seen below $T_c$ and $1/T_1$ follows $T^3$ variation, indicating the unconventional superconductivity. The finite spin susceptibility at zero-temperature limit and the anomalous increase of the NMR linewidth below $T_c$ point to a mixed state of spin-singlet and spin-triplet (or spin-septet) pairing.

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• Superconducting order parameter
• Unconventional superconductors
• Nuclear magnetic resonance