Topological systems: from insulators to superconductors

Topological quantum materials have reshaped condensed matter physics by showing that electronic phases can be classified not only by symmetry, but also by the global structure of their quantum wavefunctions. From topological insulators and semimetals to topological superconductors, these systems host robust boundary states and unconventional electronic responses that open new directions for both fundamental physics and quantum technology. A central challenge is to identify, characterize, and ultimately control the microscopic electronic structure that gives rise to these topological phenomena.

Our work has contributed to this effort across several classes of materials. In the topological insulator Bi2​Se3​, we used ARPES and spin-resolved ARPES to reveal the layer-by-layer entangled spin-orbital texture of the topological surface state, to demonstrate control of Rashba spin splitting at the surface, and to show how photoelectron spin polarization can itself be manipulated through the photoemission process. In iron pnictides, we established the three-dimensional electronic structure of LiFeAs and its connection to the coexistence of strong-coupling superconductivity and topology. In square-net systems, we identified rare-earth diantimonides as a new family of topological materials and demonstrated reversible electronic switching of topology in LaSbTe. Finally, in close collaboration with Marcel Franz, we have explored new routes to topological superconductivity, including the proposal of high-temperature topological superconductivity in twisted double-layer copper oxides.