Evidence of topological nodal lines and surface states in the centrosymmetric superconductor SnTaS2

Abstract

The discovery of signatures of topological superconductivity in superconducting bulk materials with topological surface states has attracted intensive research interest recently. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, here, we demonstrate the existence of topological nodal-line states and drumheadlike surface states in centrosymmetric superconductor $\mathrm{Sn}\mathrm{Ta}{\mathrm{S}}_{2}$, which is a type-II superconductor with a critical transition temperature of about 3 K. The valence bands from Ta $5d$ orbitals and the conduction bands from Sn $5p$ orbitals cross each other, forming two nodal lines in the vicinity of the Fermi energy without the inclusion of spin-orbit coupling (SOC), protected by the spatial-inversion symmetry and time-reversal symmetry. The nodal lines are gapped out by SOC. The drumheadlike surface states, the typical characteristics in nodal-line semimetals, are quite visible near the Fermi level. Our findings indicate that $\mathrm{Sn}\mathrm{Ta}{\mathrm{S}}_{2}$ offers a promising platform for exploring the exotic properties of the topological nodal-line fermions and helps in the study of topological superconductivity.