Measuring Friction with a Pendulum (IMAGE) University of Basel Caption The gold tip is moved across the surface of the topological insulator and experiences energy loss only at discrete, quantized energies. This is related to the image potential states that are formed over the conducting surface of the topological insulator. Credit Image: University of Basel, Departement of Physics Usage Restrictions With current release only. License Licensed 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.