Among the family of topological superconductors derived from Bi<sub>2</sub>Se<sub>3</sub>, Cu<sub>x</sub>(PbSe)<sub>5</sub>(Bi<sub>2</sub>Se<sub>3</sub>)<sub>6</sub> is unique in its surface termination of a single quintuple layer (QL) of the topological insulator (TI) Bi<sub>2</sub>Se<sub>3</sub> on an ordinary insulator PbSe. Here, we report a combined scanning tunneling microscopy (STM) and density functional theory (DFT) characterization of the cleaved surface of the parent compound (PbSe)<sub>5</sub>(Bi<sub>2</sub>Se<sub>3</sub>)<sub>6</sub> (PSBS). Interestingly, the potential disorder due to the random distribution of native defects is only Γ ∼ 4 meV, among the smallest reported for TIs. Performing high-resolution quasiparticle interference imaging (QPI) near the Fermi energy (E−E<sub>F</sub> = −1 eV to 0.6 eV) we reconstruct the dispersion relation of the dominant spectral feature and our ab initio calculations show that this surface feature originates from two bands with Rashba-like splitting due to strong spin-orbit coupling and inversion symmetry breaking. Moreover, a small hexagonal distortion of the calculated Fermi surface is seen in the full momentum space distribution of the measured scattering data. Interestingly, the scattering pattern transforms into a flower-like shape with suppressed intensity along the ΓK direction, at lower energies. However, this change is not due to the forbidden backscattering in the topological surface state in Bi<sub>2</sub>Se<sub>3</sub> but the threefold symmetry of the scattering potential itself.
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