Topology and quantum materials
From atomically thin materials to orbital textures and correlated topology
Topology describes properties of electronic states that cannot change continuously without a qualitative transformation of the system. My work investigates how these properties emerge in real materials, how interactions modify them, and how they can be identified experimentally. Atomically thin layers provide a particularly direct setting for connecting crystal structure, spin-orbit coupling, and electronic behaviour.
Indenene and the limits of edge-state protection
Our work on indenene, a single layer of indium on silicon carbide, established a route to quantum spin Hall physics on a triangular lattice. The orbital structure produces an effective honeycomb connectivity, illustrating how the electronic behaviour of a material can go beyond its atomic geometry.
More recently, we examined how robust its conducting edges actually are. Combining scanning tunnelling spectroscopy with theory, our Nature Communications (2025) study identified backscattering between different Kramers pairs in regions where several edge channels coexist. Regions with a single pair retain their protection against elastic, non-magnetic backscattering. The result clarifies why observing a band that crosses a topological gap is not, on its own, enough to establish backscattering-free transport.
- Design and realization of topological Dirac fermions on a triangular lattice · Nature Communications 12, 5396 (2021).
- Backscattering in topological edge states despite time-reversal symmetry · Nature Communications 16, 8209 (2025).
Excitons in a topological monolayer
Excitons are bound electron-hole pairs that shape how a material absorbs light. In bismuthene on silicon carbide, optical measurements and many-body calculations established that these bound states survive at room temperature within a quantum spin Hall material. The result brings optical excitations and topological electronic structure into the same atomically thin platform, motivating the study of how band geometry influences electron-hole binding and optical selection rules.
Observation of room temperature excitons in an atomically thin topological insulator · Nature Communications 13, 6313 (2022).
Imaging orbital textures
The connection between topology and spectroscopy also extends to three-dimensional materials. In Physical Review X (2025), we combined soft X-ray photoemission with first-principles theory to image orbital vortex lines in a topological semimetal. These lines trace a winding of orbital angular momentum in momentum space and reveal the structure surrounding a Weyl nodal line. The work provides a way to connect the orbital character of electronic wave functions with measurable spectroscopic patterns.
Imaging Orbital Vortex Lines in Three-Dimensional Momentum Space · Physical Review X 15, 011032 (2025).
Topology in the presence of strong correlations
Strong interactions can invalidate a description based on independent-electron bands. Our work on topological Mott insulators instead uses zeros of the electronic Green’s function to characterize these phases. The theory predicts boundary zeros and shows how they can suppress conventional edge states at an interface between a topological band insulator and a topological Mott insulator. This extends the study of bulk-boundary correspondence into the regime of strong electronic correlations.
Mott insulators with boundary zeros · Nature Communications 14, 7531 (2023).