Four bright features from surface electron gas

1. Unusual Electron Gas on Cleaved Crystal Surfaces of EuB6J.W. Allen, University of Michigan, DMR Award # 0302825 The environment of atoms making up the outer layer of a cleaved crystal ---- i.e. a crystal split open by a sharp knife-edge ---- is much different from that in the bulk of the crystal. In the bulk an atom is surrounded in all directions by other atoms but on the surface half those bulk atoms are missing. As a result the behavior of electrons on the surface can be much different than in the bulk. Such surface effects can be either useful or harmful in electronic devices and sometimes lead to novel situations of intrinsic scientific interest, as shown here. We use a technique called “photoemission spectroscopy” to make images --- known technically as “Fermi surface maps” ---- showing that the cleaved surface of a crystal of EuB6 supports a two dimensional gas of electrons likely to have novel properties worthy of further study. The surface features in the “map” are identified by “dosing” of the surface with atoms that destroy the surface electron gas. Four bright features from surface electron gas Bulk features remaining after “dosing” treatment of surface

2. Disentangling surface and bulk electronic structure of EuB6J.W. Allen, University of Michigan, DMR Award # 0302825 Training for Multi-Institutional Research This work is a good example of the multi-institutional and internationally collaborative style of research for which science students must now be trained. The photoemission spectroscopy experiments are performed at the U.S Advanced Light Source synchrotron (Lawrence Berkeley National Laboratory) by UM student Feng Wang working with ALS beamline scientist Jonathan Denlinger, using samples prepared by Zachary Fisk (University of California, Irvine). Theoretical guidance has been provided by two scientists in Switzerland, B. Delley (Paul-Scherrer Institut), and R. Monnier (Swiss Federal Technical Institute, Zurich). Education: This grant provided partial support for two graduate students, Sung-Kwan Mo (now has Ph.D. degree), and Feng Wang (will complete Ph.D. degree in 2007). The grant also supports summer research opportunities for undergraduates like Spencer Dowdall, a UM double major in physics and math.