Würzburg ToCoTronics Colloquium

Scanning probe microscopy (STM and AFM) provides local access to the electronic properties of topological insulators (TIs), including topological boundary modes, their hybridization with bulk states, and Van Hove singularities of the bulk bands. We perform tunneling current (I) and differential conductance (dI/dV) measurements on Bi₂Se₃, Bi₂Te₂Se, and Bi₂Te₃ using both metal- and CO-terminated tips. Crucially, the interpretation of these data requires comparison with calculations that account not only for the intrinsic properties of the TI but also for the electronic structure of the probing tip. The tip–sample interaction is modeled within Chen’s derivative rule. The relevant Bloch functions of the TIs are obtained from Wannier-interpolated tight-binding Hamiltonians constructed from maximally localized Wannier functions derived from first-principles DFT + GW calculations. In combination with the high spatial resolution achieved using CO-functionalized tips, this approach allows direct access to the orbital character of the band structure. Finally, on Bi₂Te₃ we observe electronic standing waves at atomic step edges, originating from the hexagonal warping of the Dirac cone. These real-space oscillations provide a direct probe of the dispersion relation of the topological boundary modes.

[1] C. Setescak, I. Aguilera, A. Weindl, M. Kronseder, A. Donarini and Franz J. Giessibl, Physical Review B 111, 165305 (2025) https://doi.org/10.1103/PhysRevB.111.165305