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arXiv · 2502.02312

Quasiparticle interference on the surface of Bi$_{\mathbf{2}}$Se$_{\mathbf{3}}$ terminated (PbSe)$_{\mathbf 5}$(Bi$_{\mathbf 2}$Se$_{\mathbf 3}$)$_{\mathbf 6}$

Mahasweta Bagchi·Philipp Rüßmann·Gustav Bihlmayer·Stefan Blügel·Yoichi Ando·Jens Brede
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Abstract

Among the family of topological superconductors derived from {\BiSe}, $\mathrm{Cu}_x(\mathrm{PbSe})_{5}(\mathrm{Bi}_{2}\mathrm{Se}_{3})_{6}$ is unique in its surface termination of a single quintuple layer (QL) of the topological insulator (TI) \BiSe{} 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 $(\mathrm{PbSe})_{5}(\mathrm{Bi}_{2}\mathrm{Se}_{3})_{6}$ (PSBS). Interestingly, the potential disorder due to the random distribution of native defects is only $\Gamma \sim 4~\mathrm{meV}$, comparable to the smallest reported for TIs. Performing high-resolution quasiparticle interference imaging (QPI) near the Fermi energy ($E-E_\mathrm{F} = -1~\mathrm{eV}~\mathrm{to}~0.6~\mathrm{eV}$) 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, only a small hexagonal distortion of the calculated Fermi surface is seen in the full momentum space distribution of the measured scattering data. Nevertheless, the scattering pattern at lower energies transforms into a flower-like shape with suppressed intensity along the $\overline{\Gamma \mathrm{K}}$ direction. We show that this effect is not due to the forbidden backscattering in the spin-momentum locked surface state in Bi$_2$Se$_3$ but reflects the threefold symmetry of the scattering potential.

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Mahasweta Bagchi, Philipp Rüßmann, Gustav Bihlmayer, Stefan Blügel, Yoichi Ando, Jens Brede. 2025-02-04. Quasiparticle interference on the surface of Bi$_{\mathbf{2}}$Se$_{\mathbf{3}}$ terminated (PbSe)$_{\mathbf 5}$(Bi$_{\mathbf 2}$Se$_{\mathbf 3}$)$_{\mathbf 6}$. https://doi.org/10.1103/h8v9-sl53

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