Evidences of Topological Surface States in the Nodal-Line Semimetal SnTaS 2 Nanoflakes.

Exploring the topological surface state of a topological semimetal by the transport technique has always been a big challenge because of the overwhelming contribution of the bulk state. In this work, we perform systematic angular-dependent magnetotransport measurements and electronic band calculations on SnTaS 2 crystals, a layered topological nodal-line semimetal. Distinct Shubnikov-de Haas quantum oscillations were observed only in SnTaS 2 nanoflakes when the thickness was below about 110 nm, and the oscillation amplitudes increased significantly with decreasing thickness. By analysis of the oscillation spectra, together with the theoretical calculation, a two-dimensional and topological nontrivial nature of the surface band is unambiguously identified, providing direct transport evidence of drumhead surface state for SnTaS 2 . Our comprehensive understanding of the Fermi surface topology of the centrosymmetric superconductor SnTaS 2 is crucial for further research on the interplay of superconductivity and nontrivial topology.