学术报告：Direct determination of exciton wave-functions, by the photo-electron emission experiment, without theoretical calculations
报告题目：Direct determination of exciton wave-functions, by the photo-electron emission experiment, without theoretical calculations
报 告 人：Prof. Keiichiro Nasu（日本高能加速器研究机构，物质构造科学研究所）
The free exciton is the most elementary optical excitation in insulating solids, being a coulombic bound state between electron and hole in their relative space. At present, however, its wave function can be known, only by some theoretical calculations for valence and conduction band energy curves, as well as for the effective electron-hole attraction. Here, we study a time and momentum resolved photo-electron emission (PEE) process from a free exciton in insulating crystals. In this PEE process, only the electron constituting the exciton is suddenly emitted out of the crystal, while the hole constituting the exciton is still left inside and forced to be recoiled back to its original valence band. This recoil on the hole is surely reflected in the spectrum of the PEE with a statistical distribution along the momentum-energy curve of the valence band. This distribution is nothing but the wave function of the exciton, since it shows how the electron and the hole are originally bound together. Thus, the momentum-resolved PEE can directly determine the exciton wave function without any theoretical calculations. These problems are clarified, taking the Γ and the saddle point excitons in GaAs and Cu2O, as typical examples.
Keiichiro Nasu, Professor, Division of Theoretical Solid State Physics, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK).
Faculty of Science of Tohoku University (Sendai, Japan), from April 1965 to March 1970 (Bachelor of Science).
Physics Department of Tohoku University (Sendai, Japan), from April 1970 to March 1975 (Post-graduate Level).
Ph.D. of Physics, March 1975, from Tohoku University.
Assistant Professor of Institute for Solid State Physics of Tokyo University, from July 1977 to October 1982.
Associate Professor of Institute for Molecular Science, from November 1982 to October 1992.
Professor of National Laboratory for High Energy Physics, from November 1992 to March 1997.
Professor of Theoretical Solid State Physics Division, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), from April 1997.
Dean, School of Mathematical and Physical Study, Graduate University for Advanced Study, (April 2001-March 2002).
Group Leader of electronic solid state physics, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), from April 2006.
Field of Research:
Solid State Theory (, about 210 papers on), Electron-phonon interactions in solids, Self-trapping of excitons and electrons, Peierls transitions, CDW, Solitons, superconductivities, X-ray nonlinear processes in solids, Photoemission and electron Correlations in solids, Ferromagnetism, Photo-induced phase transitions.