Dynamics of Correlated Materials
Emmy Noether Group Laurenz Rettig
Dynamics of Correlated Materials
Emmy Noether Group Laurenz Rettig
Dynamics of Correlated Materials
Emmy Noether Group Laurenz Rettig

News Post
New Preprint: Time- and Momentum-resolved Signatures of Edge States in a 2D Topological Insulator
Aug 2021

In the quest to continue Moore´s law, utilizing the electron´s spin degree of freedom poses a promising approach. A material class that intrinsically enables efficient spintronic applications are quantum spin Hall (QSH) insulators, also termed 2D topological insulators, as they allow for dissipationless spin-currents in their edges. However, exploiting the transport properties of such edge states is so far restricted to cryogenic temperatures, as only a few QSH materials with small bulk band gaps are available. Here, graphene-like 2D structures of heavy atoms, most notably bismuthene, i.e., a honeycomb lattice of Bi atoms on a semiconductor substrate, offer a route to QSH conductivity far beyond room-temperature due to their large spin-orbit coupling.

In our recent study (arXiv link), we present a detailed investigation of the ultrafast electron dynamics of bismuthene using time- and angle-resolved photoemission spectroscopy and scanning tunneling microscopy. A detailed mapping of the transiently occupied conduction band after optical excitation confirms the predicted large indirect bulk band gap, a prerequisite for high-temperature QSH applications. Intriguingly, within the bulk band gap, we observe clear signatures of the elusive edge states and track their decisive role in the ultrafast relaxation of photocarriers.