Topological surface states in superconducting CaBi2

Topological superconductors are materials in which superconductivity is closely entangled with topological electronic states. This provides a promising route to create Majorana bound states that are of fundamental importance to fault-tolerant quantum computation. In this paper, the recently discovered superconductor ${\mathrm{CaBi}}₂$ has been identified as a three-dimensional topological material. Spin-split topological surface states intersecting the Fermi energy are experimentally observed via spin- and angle-resolved photoemission spectroscopy. They are highly consistent with theoretical calculations. Furthermore, the layer-locked spin structure of ${\mathrm{CaBi}}₂$ is revealed via the layer-resolved spin texture analysis. These results unambiguously reveal the topological properties of the spin-polarized electronic structure in ${\mathrm{CaBi}}₂$ and provide important clues in the search for Majorana fermions in Bi-based topological superconductors.