Spectroscopic Signatures of Edge States in the Quantum Spin Hall System Bismuthene

PC Online Talk
Date: Oct 8, 2020
Time: 11:00 AM (Local Time Germany)
Speaker: Julian Maklar
FHI Department PC

Quantum spin Hall (QSH) systems are two-dimensional topological insulators with promising device applications due to dissipationless spin currents in their edges. However, most QSH systems realized so far have required cryogenic temperatures due to their small bulk gap sizes. A candidate for a high-temperature QSH material is Bismuthene, i.e., a monolayer of bismuth arranged in a honeycomb lattice on a silicon carbide substrate, which features a semiconducting band structure with an indirect band gap of 0.8 eV.

Additionally, scanning tunneling spectroscopy measurements have revealed conductive edge channels located at substrate steps and domain boundaries consistent with theory predictions. Here, we investigate the electronic structure of Bismuthene upon ultrafast photoexcitation via time- and angle-resolved photoemission spectroscopy (trARPES). We map out the unoccupied electronic band structure and observe faint spectral weight inside the band gap, which we attribute to metallic edge channels. In addition, we track the full relaxation pathway of excited carriers and observe a complete recovery to the ground state within few hundred femtoseconds – several orders of magnitude faster than in conventional indirect semiconductors - which further hints towards the presence of conductive edge states.