Observation of two-dimensional bulk electronic states in the superconducting topological insulator heterostructure Cux(PbSe)5(Bi2Se3)6: Implications for unconventional superconductivity

We have performed angle-resolved photoemission spectroscopy (ARPES) on Cu-x(PbSe)(5)(Bi2Se3)(6) [(CPSBS); x = 1.47], a superconductor derived from a topological insulator heterostructure, to elucidate the electronic states relevant to the occurrence of possible unconventional superconductivity. Upon Cu intercalation into the parent compound (PbSe)(5)(Bi2Se3)(6), we observed a distinct energy shift of the bulk conduction band due to electron doping. Photon-energy-dependent ARPES measurements of CPSBS revealed that the observed bulk band forms a cylindrical electronlike Fermi surface at the Brillouin-zone center. The two-dimensional nature of the bulk electronic states puts strong constraints on the possible topological character of the superconducting state in CPSBS.