  Two quintuple layers of strong topological insulator Bi2Se3 are coupled by a
Bi bilayer in BiSe crystal. We investigated its electronic structure using
angle resolved photoelectron spectroscopy to study its topological nature.
Dirac like linearly dispersive surface state bands are observed on the 001
surface of BiSe and Sb doped BiSe, similar to Bi2Se3. Moreover, the lower part
of the SSBs buries deep in the bulk valence band. Overlap region between the
SSBs and BVB is large in Sb doped system and the SSBs deviate from the Dirac
like linear dispersion in this region.
  These results highlight the role of interlayer coupling between the Bi
bilayer and the Bi2Se3 QLs.
  Furthermore, we observed a large intensity imbalance in the SSBs located at
the positive and negative k parallel directions. This asymmetry pattern
gradually reverses as the excitation energy scans from low 14eV to high 34eV
value. However, we did not observe signal of surface magnetization resulting
from the intensity imbalance in SSBs due to hole-generated uncompensated spin
accumulation in the photoexcitation process. The main reason for this could be
the faster relaxation process for photo hole due to the presence of the Bi
bilayer between the adjacent Bi2Se3 QLs. The observed photon energy dependent
intensity variation could be a signature of the mixing between the spin and the
orbit texture of the SSBs.
