Success in Measuring the Accurate Electronic Band Structure of Solids

A group centered by Dr. Shigenori Ueda, a Researcher at the NIMS Beamline Station at SPring-8 (Station Leader: Dr. Osami Sakata), Research Network and Facility Services Division, National Institute for Materials Science (President: Dr. Sukekatsu Ushioda), succeeded for the first time in the world in measuring the band dispersion of solids by angle-resolved photoelectron spectroscopy in the hard X-ray region. The samples used in this research were tungsten as a representative example of a metallic material, and gallium arsenide as a representative semiconductor. The work was performed utilizing a combination of the theoretical approach called first-principles calculation and a hard X-ray photoelectron spectroscopic instrument, which enables ones to measure the electronic states in the interiors of solids with the world’s highest performance, at the third-generation synchrotron radiation facility SPring-8, Japan.
  This research has been carried out as joint research with the University of California, Davis, the Lawrence Berkeley National Laboratory, the University of Erlangen-Nuremberg, the University of Mainz, the Jülich Research Centre, and the Ludwig Maximilian University of Munich.
  As a result of this achievement, it is now possible to measure the accurate electronic band dispersion in the interiors of various functional materials. This is expected to provide important guiding principles for the creation of new functional materials.
  The results of this research has been published previously in the electronic version of Nature Materials, which is a sister journal of Nature, at 2:00 a.m. on August 15 (Monday) Japan time (at 18:00, August 14, London local time).

Figure: Experimental results of hard X-ray angle-resolved photoelectron spectroscopy and theoretical calculations for tungsten. (a) Measured results at room temperature (300 K). Band dispersion is not observed when the Debye-Waller factor is small (W=0.09). (b) Measured results at low temperature (30 K). Band dispersion can be observed when W=0.45. (c) Comparison of a theoretical calculation (green) and the experimental results after subtracting the background from (b). (d) Theoretical calculation considering photoelectron excitation probability. Band dispersion could not be seen at room temperature, but it was able to clearly observe band dispersion at low temperature. One can see that the tendency of the theoretical calculations is in good agreement with the experimental results.