Mathematical Trick (IMAGE) Forschungszentrum Juelich Caption A mathematical trick -- an image showing the energy levels of surface electrons in reciprocal space -- reveals the area of maximum energy efficiency. This is found where the points of the double cones lie at the so-called Fermi level (grey band, middle double cone), and indicates the highest energy level that an electron can possess in the material under investigation with no outside energy supply. By varying the layer thickness, the cones can be altered and with them the conditions for spin transport. The red band symbolizes the conduction band, the green one, the valence band. Credit Forschungszentrum Jülich Usage Restrictions Image may only be used with approprate credit. Image may only be used in conjunction with media reports about Forschungszentrum Jülich. 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.