Antiferromagnetic Spin Fluctuations and Unconventional Superconductivity in Topological Superconductor Candidate YPtBi Revealed by Pt195 -NMR

We report Pt195 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/T1 divided by temperature (T), 1/T1T, increases with decreasing T, implying the existence of antiferromagnetic spin fluctuations. In the superconducting state, no Hebel-Slichter coherence peak is seen below Tc and 1/T1 follows T3 variation, indicating the unconventional superconductivity. The finite spin susceptibility at zero-temperature limit and the anomalous increase of the NMR linewidth below Tc point to a mixed state of spin-singlet and spin-triplet (or spin-septet) pairing.Received 14 November 2022Revised 22 March 2023Accepted 16 May 2023DOI:https://doi.org/10.1103/PhysRevLett.130.266002© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasSuperconducting order parameterPhysical SystemsUnconventional superconductorsTechniquesNuclear magnetic resonanceCondensed Matter, Materials & Applied Physics