1. 橋本佑介 A,B 三野弘文 A 、山室智文 A 、蒲原俊樹 A 、神原大蔵 A 、松末俊夫 B Jigang Wang C 、 Chanjuan Sun C 、河野淳一郎 C 、嶽山正二郎 D 千葉大院自然 A 、千葉大工 B 、ライス大 ECE C 、東大物研 D Y. Hashimoto A,B H. Mino A, T. Yamamuro A, T. Kamohara A, D. Kanbara A, T. Matsusue B, J. Wang C, C. Sun C, J. Kono C, S. Takeyama D Graduate School of Science and Technology, Chiba Univ. A 、 Department of Engineering, Chiba Univ. B, ECE Dept., Rice Univ. C 、 ISSP, Univ. of Tokyo D 13aXD-14 High excitation effects in dilute magnetic semiconductor CdMnTe 希薄磁性半導体 CdMnTe における強励起効果

2. Magnetic Polarons Mn spin Exciton spin e h Free Exciton Magnetic Polaron (FEMP) Localization only by sp-d exchange interaction A Golnic, et. al. J. Phys. C16, 6073 (1983) M. Umehara, Phys. Rev. B 68, 193202 (2003) Photo-induced ferromagnetism via the FEMP

3. Free exciton magnetic polaron (FEMP) in CdMnTe High quality CdMnTe sample with low Mn concentration He-Ne laser 76 MHz Ti:Sapphire laser 250 kHz OPA laser 1 kHz OPA laser Exciton density 10 12 – 10 20 [cm-3] CW and Time-resolved Photoluminescence Current work : Alloy potential fluctuation : Small x = 5 ~ 10% → FEMP energy : Large S. Takeyama, J. of Crys. Growth, 184-185 (1998) 917-920 Mn Concentration [%] Localization energy 105 Alloy Potential fluctuation Localization energy of Magnetic Polaron

4. Free Exciton Magnetic Polarons FEMP Bipolaron Ferromagnetic Phase Transition via Free Exciton Magnetic Polarons ?

5. Experimental Setup for PL measurements Laser CCD or Streak camera Spectro- meter Sample 1.4 K Bulk Cd 1-x Mn x Te x = 5% Cd 1-y Mg y Te Cd 0.95 Mn 0.05 Te GaAs

6. Lasers LaserExciton density [/cm 3 ]rsrs Wavelength He-Ne2.2 x 10 13 33634 nm Ti: Sapphire2.8 x 10 15 6.6400 nm 250KHz OPA8.6 x 10 17 1700 nm 1KHz OPA2.2 x 10 20 0.15634 nm 1 kHz OPA 250 kHz OPA Ti: Sapphire He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12 1 2 10 0.1 100 n rsrs Excitation intensity: 1mW, Focus size: 200  m, O.D. 1 a B = 6.7 nm  n Mott = 7.9 x 10 17 [cm-3]

7. Low Excitation Limit Exciton Density 10 12 - 10 14 [cm -3 ] Absorption: 4.2 K, PL: 1.4K PL Light source ： He-Ne 633nm Photoluminescence Absorption Photon energy [eV] Distinct PL line of the FEMP appear !! FEMP binding energy  1.8 meV Ti: S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12 BX

8. Photoluminescence Exciton Density 10 15 – 10 16 [cm -3 ] Ti:S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12 Excitation intensity normalized PL Exciton density 10 15, 10 16 [cm -3 ] FEMP PL intensity: Saturate FX PL intensity: Increase BX

9. Time Resolved Photoluminescence Exciton Density 8.6 x 10 17 cm -3 10 20 Ti: S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 12 AB 1.674eV 1.667eV BXEHP

10. Time Resolved Photoluminescence Exciton Density 8.6 x 10 17 cm -3 A: 1.674 eV  ~ 150 ps  Biexciton B: 1.667 eV  < 30 ps  ? A Inverse Boltzman 10 20 Ti: S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 12

11. Many Body Effect of FEMPs Coupled two FEMPs has been expected to be more stable than single FEMP Bi-polaron Bi-exciton

12. Photoluminescence Exciton Density > Mott Density Ti: S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12 Electron hole plasma  I 4.2 Biexciton  I 1.6 I = 5.6 × 10 18 [cm -3 ]

13. Exciton Density Dependence of Origin of Photoluminescence FEMP Electron hole Plasma Biexciton Ti: S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12

14. Summary PL measurements Exciton density: 10 12 – 10 20 [cm -3 ] FEMP  Biexciton Electron hole plasma Future work Spin Dynamics Under Strong Excitation

15. Free Exciton Magnetic Polaron Hole mass: Electron mass: Hole 14.4Å Electron 64Å The number of Mn ion electron:481 hole:~5.5 Mn spin

16. Exciton Density Dependence When the exciton density is above 10 18 cm -3 FEMP may disappear Ti: S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12 Excitation intensity normalized FEMP PL int. FEMP binding energy

17. Spin Relaxation Dynamics 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12 5K

18. Time Resolved Photoluminescence Ti: S 1 kHz OPA 250 kHz OPA He-Ne 10 13 10 14 10 15 10 16 10 17 10 18 10 19 10 20 10 12 250 kHz OPA laser76 MHz OPA laser 1.4K

19. Experimental Setup for PL measurements chopper Movable mirror Sample 13 K 1kHz OPA&CPA He-Ne Photodiode Spectro- meter Lock-in Amplifier

20. Discussions

21. Excitation Dependence of the PL Intensity Excited with Ti:Sapphire Laser

22. Peak position [eV] Binding Energy [meV] Absorption1.6748 Biexciton1.67410.7 FEMP1.67222.6 Estimate by the E BX (4.1 meV) on CdSe

23. Purpose