Pressure-induced superconductivity in the Zintl topological insulator SrIn2As2

The Zintl compound $A{\mathrm{In}}_{2}{X}_{2}$ $(A=\mathrm{Ca}, \mathrm{Sr}, \text{and} X=\mathrm{P}, \mathrm{As})$, as a theoretically predicted nonmagnetic topological insulator, requires experiments to understand its electronic structure and topological characteristics. In this paper, we systematically investigate the crystal structures and electronic properties of the Zintl compound $\mathrm{Sr}{\mathrm{In}}_{2}{\mathrm{As}}_{2}$ under both ambient and high-pressure conditions. By means of angle-resolved photoemission spectroscopy, we observe the overall band structures and ``tails'' of the topological surface states on the (001) surface that qualitatively agree well with ab initio calculations, thus suggesting $\mathrm{Sr}{\mathrm{In}}_{2}{\mathrm{As}}_{2}$ as a topological insulator. Interestingly, application of pressure effectively tunes the crystal structure and electronic properties of $\mathrm{Sr}{\mathrm{In}}_{2}{\mathrm{As}}_{2}$. Superconductivity is observed in $\mathrm{Sr}{\mathrm{In}}_{2}{\mathrm{As}}_{2}$ for pressure where the temperature dependence of the resistivity changes from a semiconductinglike behavior to that of a metal. The observation of nontrivial topological states and pressure-induced superconductivity in $\mathrm{Sr}{\mathrm{In}}_{2}{\mathrm{As}}_{2}$ provides crucial insights into the relationship between topology and superconductivity, and also stimulates further studies of superconductivity in topological materials.