Link between superconductivity and a Lifshitz transition in intercalated BiSe

In a topological superconductor the bulk of the sample is fully gapped while a topologically protected gapless state resides on the surface. Intercalation of Cu, Sr or Nb between the quintuple layers of the topological insulator Bi₂Se₃ increases the carrier concentration and leads to superconductivity. It was suggested that the superconducting state in these compounds is topological. Here we study the electronic structure of Sr-intercalated Bi₂Se₃ using angle resolved photoemission spectroscopy (ARPES) and Shubnikov-de Haas (SdH) oscillations. We show that despite the relatively low Hall number, the carrier density is large and the resulting Fermi surface is cylindrical-type. We suggest that superconductivity in intercalated Bi₂Se₃ is more likely in such quasi-2D open Fermi surface.