ARPES and K-Space Map (image) DOE/Lawrence Berkeley National Laboratory Caption The diagram at right maps the electronic states of bismuth selenide in momentum space. ARPES, at left, can directly create such maps with photoelectrons. A slice through the conduction cone at the Fermi energy maps the topological insulator's surface as a circle (upper left); here electron spins and momenta are locked together. Initial ARPES measurements in this experiment were made with p-polarized incident light in the regions indicated by the green circle and line, where the spin polarization of the photoelectrons is consistent with the intrinsic spin polarization of the surface. Credit Lawrence Berkeley National Laboratory Usage Restrictions with credit as given 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.