Three excitons (IMAGE) University of Würzburg Caption Three excitons (pairs consisting of an electron and an electron hole) on the topological insulator bismuthene. Due to the honeycomb atomic structure, electrons can only flow along the edges. Credit Pawel Holewa Usage Restrictions no restrictions License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.