Experiment Verifies Quasi-Particle Model for Diamond
Researchers using angle-resolved photoelectron spectroscopy on Beamline 8.0.1 have reported the first quantitative experimental verification of the theoretical electronic structure of diamond. The theoretical structure they have verified is based on a "quasi-particle" model of electron interactions within the diamond lattice. This result for diamond, a semiconductor with a relatively simple electronic structure, helps pave the way for work with more complex materials such as high-temperature superconductors. Such work leads in turn toward the design of advanced materials with custom properties.
The diagram above shows the band structure for carbon (111), also known as diamond. The calculated band structure is shown in green; the angle-resolved photoelectron spectroscopy data is shown in shades of orange and white, with lighter colors representing higher detected electron intensities. The horizontal axis shows crystal momentum, indexed by letters representing points of symmetry in the band structure.
The experimental and theoretical data shown here are in excellent agreement for the characteristics modeled by the theory. The theoretical quasi-particle calculations correctly predict the density of states, or energy/crystal momentum locations at which electrons could possibly be found. However, the calculations do not take into account some of the rules (known as matrix-element effects) governing electron transition probabilities in the photoemission process, and these rules restrict the actual electron intensities to portions of the theoretical curve. The fuzziness of the experimental data is due to lifetime broadening (an instance of the Heisenberg uncertainty principle), experimental resolution, and other effects that are not yet fully modeled in quasi-particle band calculations.
This research was conducted by I. Jiménez, L.J. Terminello (co-principal investigator), D.G.J. Sutherland, and J.A. Carlisle (Lawrence Livermore National Laboratory); E.L. Shirley (National Institute of Standards and Technology); and F.J. Himpsel (co-principal investigator, University of Wisconsin at Madison) using the display analyzer at Beamline 8.0.1. Funding was provided by the U. S. Department of Energy (Contract No. W-7405-ENG-48), the National Science Foundation (Award No. DMR-9632527), and the Spanish Ministerio de Educación y Ciencia.
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