Observation of spin-polarized surface states in the nodal-line semimetal SnTaS2

The superconductor ${\mathrm{SnTaS}}₂$ is theoretically predicted to be an intriguing topological nodal line semimetal without consideration of spin-orbit coupling. By carrying out angle-resolved photoemission (ARPES) and spin-resolved ARPES measurements combined with band structure calculations, we have provided a complete picture of the electronic structure and spin polarization property for the prominent surface states of ${\mathrm{SnTaS}}₂$. The low-energy electronic states are dominated by surface states; two of them are from the S-terminated surface, while four of them are from the Sn-terminated surface. These give rise to interesting Fermi surface topology of ${\mathrm{SnTaS}}₂$: three pockets located at $\overline{\mathrm{\ensuremath{\Gamma}}}, \overline{M}$ and $\overline{K}$ for the S-terminated surface and two pockets surrounding $\overline{\mathrm{\ensuremath{\Gamma}}}$ and $\overline{K}$ for the Sn-terminated surface. We further reveal that two surface states that cross the Fermi level are spin-polarized. Since ${\mathrm{SnTaS}}₂$ is also a superconductor, our observations indicate that it may provide a new platform to explore topological superconductivity and other exotic properties.