First detection of excitons in a topological insulator

A new study has demonstrated a major innovation in light-driven electronics using 2D material samples of bismuthine. An international team of researchers collaborating with the Würzburg-Dresden Cluster of Excellence ct.qmat, led by Ralph Claessen, have achieved the first detection of excitons – electrically neutral quasiparticles – in a topological insulator, a breakthrough that could lead to a new generation of light-driven microelectronic devices and quantum technologies. The research into smart material design for future quantum technologies focused here on topological insulators, as they allow the lossless conduction of electrical current and robust information storage. Topological insulators previously depended on applying electrical voltages to manipulate currents, an approach used in standard computer chips. However, if the exotic material properties are based on electrically neutral particles, which are neither positively nor negatively charged, then electric voltage is no longer effective, with these quantum phenomena needing other tools, such as light, to be generated. As detailed in the journal Nature Communications [Skyperek et al. Nat. Commun. (2022) DOI: 10.1038/s41467-022-33822-8], this is the first time excitons have been generated and experimentally detected in a topological insulator. The research offers a new way to control electrons optically in solid-state physics, a principle could lead to innovative kinds of electronic components.   Excitons seem to act like independent particles but really represent an excited electronic state that can only be produced in some kinds of quantum matter, with excitons here being activated in a topological insulator for the first time. As Claessen pointed out, “We created excitons by applying a short light pulse to a thin film consisting of just one single layer of atoms”. He added, “The interaction between light and excitons means we can expect new phenomena in such materials. This principle could be used, for example, to generate qubits,”.   Excitons have been explored in other 2D semiconductors and viewed as information carriers for light-driven components, while qubits are computing units for quantum chips that can solve tasks quicker than conventional supercomputers. Using light instead of electrical voltage allows for quantum chips with much faster processing speeds.   Aided by sophisticated materials design, the team began with bismuthine, with the atoms of the single layer being arranged in a honeycomb pattern. The heavy atoms in bismuthine allow it to conduct electricity along the edge without loss, even at room temperature.   The team are now looking into quasiparticles and whether bismuthine’s topological properties are transferred to excitons. If this can be shown, it could lead to the construction of topological qubits, which are considered particularly robust compared to their non-topological counterparts.