Effect of Barium Codoping on Superconductivity in SrxBi2Se3

A structural reason for superconductivity in a Cu-, Sr-, or Nb-atom-doped Bi2Se3 topological insulator is still unclear. To understand this reason, a codoping approach has been developed and BaySrxBi2Se3 single crystals with different x and y values have been grown. The composition and structural and transport properties of the grown crystals have been studied. With X-ray diffraction data, it has been shown that barium and strontium intercalate the system, although barium is present in the structure in a very small amount. The addition of barium surprisingly destroys superconductivity, slightly changing the lattice constants, the strontium doping level of the crystal matrix, and the electron density. Thus, a key role of a certain coordination arrangement of positions of strontium atoms between Bi2Se3 quintuples for achieving superconductivity in this material has been demonstrated.