Topological surface states of Bi-doped ${\mathrm{PbSb}}_2{\mathrm{Te}}_4 \left[\mathrm{Pb}{\left({\mathrm{Bi}}_{0.20}{\mathrm{Sb}}_{0.80}\right)}_2{\mathrm{Te}}_4\right]$ are investigated through analyses of quasiparticle interference (QPI) patterns observed by scanning tunneling microscopy. Interpretation of the experimental QPI patterns in the reciprocal space is achieved by numerical QPI simulations using two types of surface density of states produced by density functional theory calculations or the Fu's surface state model [Phys. Rev. Lett. 103, 266801 (2009)]. We found that the Dirac point (DP) of the surface state appears in the bulk band gap of this material and, with the energy being away from the DP, the isoenergy contour of the surface state is substantially deformed or separated into segments due to hybridization with bulk electronic states. These findings provide a more accurate picture of topological surface states, especially at energies away from the DP, providing valuable insight into the electronic properties of topological insulators.

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• Electronic structure
• Surface states
• Topological insulators
• Two-dimensional electron system
• Scanning tunneling microscopy