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Lecture Tetsuo Ogawa


12 May 2009 FWN-Building 5111.0080, Nijenborgh 4, 9747 AG, Groningen
Speaker: Prof. Dr. Tetsuo Ogawa
Affiliation: Osaka University, Japan
Title: Quantum cooperative phenomena in photoexcited semiconductors: Exciton Mott transition and electron-hole pair condensation
Date: Tue May 12, 2009
Start: 10.30
Location: FWN-Building 5111.0080
Host: Paul van Loosdrecht
Telephone: +31 50 363 8149


We study theoretically quantum cooperative phenomena in "electron-hole (e-h) systems," which are photoexcited states of semiconducting or insulating solids, composed of electrons in a valence band and positive-charged holes (whose number is identical to that of electrons) in the valence band. In the lower-density regime, an electron and a hole form a quasi-bosonic bound state "exciton," resulting in an insulating exciton gas phase. In the higher-density regime, excitons break to electrons and holes due to the screening and the Pauli blocking, and the metallic "e-h plasma" appears. The transition between these two phases is called the "exciton Mott transition," which is investigated with the dynamical mean-field theory (DMFT) and with the slave-boson mean-field theory for the high-dimensional e-h Hubbard model [1]. In lower temperature, the bosonic exciton gas can be turned into the Bose-Einstein condensed (BEC) phase; on the other hand, the fermionic e-h plasma may  be condensed to a superconducting-like state (e-h BCS state). We discuss relation between these two condensates using the self-consistent t-matrix and local approximations [2]. We will mention also lower-dimensional cases, where the biexciton crystallization is expected [3]. Comparison of the e-h systems with other physical systems, e.g., plasmas, cold atoms, and hadron systems will also be made.

[1] T. Ogawa, Y. Tomio, K. Asano, J. Phys.: Cond. Mat. 19, 295205 (2007); T. Ogawa, Y. Tomio, J. Lumin. 128, 1022 (2008); K. Asano, T. Ogawa, Physica E 40, 1249 (2008).
[2] Y. Tomio, K. Honda, T. Ogawa, Phys. Rev. B 73, 235108 (2006); J. Lumin. 128, 1032 (2008).
[3] K. Asano, T. Ogawa, J. Lumin. 112, 200 (2005).

Last modified:22 October 2012 2.30 p.m.