A team of scientists has discovered long-lasting excitons in a topological material, which could lead to new possibilities for optoelectronics and quantum computing. Excitons are quasiparticles created when a semiconductor absorbs light. They consist of an excited electron linked to a lower-energy electron vacancy or hole, but they typically have a short lifespan until the electron and hole combine, limiting their usefulness in practical applications.
To make progress in quantum computing and create more sustainable electronics, researchers require longer exciton lifetimes and novel ways of transferring information that do not rely on the charge of electrons, according to Alessandra Lanzara, who led the study. Lanzara is a senior faculty scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and a UC Berkeley physics professor.
In a topological insulator, electrons can only move on the surface. By creating an exciton in such a material, the researchers aimed to create a state in which an electron trapped on the surface was linked to a hole that remained confined in the bulk. Such a state would be spatially indirect, extending from the surface into the bulk, and could retain the unique spin properties inherent to topological surface states.
Using a state-of-the-art technique known as time-, spin-, and angle-resolved photoemission spectroscopy, the team investigated the properties of electrons in a material using ultrafast pulses of light. They worked with bismuth telluride, a well-studied topological insulator that provided the specific properties they required.
The team analyzed the formation of the excitonic state and characterized its interaction with other charge carriers in the material. They also measured the state’s spin character and demonstrated the persistence of the topological material’s strong spin polarization in the excitonic state. The research is published in the journal Nature.