  We have performed angle-resolved photoemission spectroscopy (ARPES) on
Cux(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 suggests the
occurrence of odd-parity Eu pairing or even-parity d-wave pairing, both of
which may provide a platform of Majorana bound states in the superconducting
state.
