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スペクトルおよび 時間分解光誘起ファラデー回転による 磁気ポーラロンスピン配向過程

21aTH-4. スペクトルおよび 時間分解光誘起ファラデー回転による 磁気ポーラロンスピン配向過程. Spin polarization dynamics on magnetic polaron by means of spectrum- and time-resolved Faraday rotation. 橋本　佑介、三野　弘文、山室　智文、神原　大蔵、松末　俊夫 A 、嶽山　正二郎 B,C. 千葉大院自然科学、千葉大工 A 、 千葉大理 B 、 東大・物性研 C. Motivation. x = 5 ~ 10% → FEMP energy : Large.

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スペクトルおよび 時間分解光誘起ファラデー回転による 磁気ポーラロンスピン配向過程

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  1. 21aTH-4 スペクトルおよび 時間分解光誘起ファラデー回転による 磁気ポーラロンスピン配向過程 Spin polarization dynamics on magnetic polaron by means of spectrum- and time-resolved Faraday rotation 橋本　佑介、三野　弘文、山室　智文、神原　大蔵、松末　俊夫A、嶽山　正二郎B,C 千葉大院自然科学、千葉大工A、千葉大理B、 東大・物性研C

  2. Motivation x = 5 ~ 10% → FEMP energy : Large Alloy potential fluctuation : small Free exciton magnetic polaron (FEMP) in CdMnTe Localized energy of Magnetic Polaron Localized energy Alloy Potential 5 10 Mn Concentration [%] Method : High quality sample with low Mn concentration Spectrum- and time-resolved Photo-induced Faraday rotation (SRPIFR, TRPIFR) Aim : Photo-induced Magnetism

  3. Sample Bulk-Cd1-xMnxTe x = 5% GaAs Cd1-xMgxTe Cd1-xMnxTe Quartz disk The opaque GaAs substrate was removed CdMgTe layer is transparency in CdMnTe resonance of this sample

  4. Absorption and Photoluminescence PL Light source：He-Ne 633nm 4.2K Distinct PL line of the FEMP appear !!

  5. Theoretical study ofthe self-trapped FEMP Mn concentration = 10 % Adiabatic Potential (meV) 1/aB Inversion of the extension of the center of mass motion Masakatsu Umehara

  6. Experimental setup of PIFR Time Delay 76MHz Pump Ti:Sapphire Laser Probe B.S. λ/2 λ/4 λ/2 EX absorption Laser spectrum Sample 1.4 ~ 300K 0 ~ 6.9T Lock-in Amplifier Polarization Beam Splitter Optical Bridge

  7. Temporal profiles of PIFR 5K n: refractive index frequency l: sample thickness c: light speed

  8. Laser spectrum Fourier transfer spectrum filter Grating Mirror lens slit Mirror Probe beam Band edge exciton resonance absorption EX FWHM Pump：6.2meV (2.8nm) Probe：1.6meV (0.7nm)

  9. PIFR excitation energy dependence Pump FEMP FX Probe FX： Exciton spin relaxation (8ps) FEMP： Exciton spin relaxation 　　　　＋ Long decay process > 13ns Mn spin relaxation ≈100ns T. Strutz et.al, Phys. Rev. Lett 68, 3912 Ferromagnetic spin alignment of the Mn ions via the FEMP !!!

  10. PIFR spectrum at 13ns FEMP resonance Long decay signal FX resonance No signal FEMP FX Excitation energy Δt = 13ns Exciton feels the effective magnetic field of the ferromagnetically aligned Mn spins FEMP Free exciton Mn ion

  11. summary The excitation energy dependence of the spectrum- and time-resolved photo-induced Faraday rotation have been observed. Under the FEMP resonance excitation, the PIFR signal shows the quite long decay signal that last more than 13ns. We attribute this long decay process to the Mn spin orientation via the FEMP formation. In the case of the FEMP resonance excitation, the PIFR spectrum at 13ns indicates the exciton energy splitting via the effective magnetic field that should be induced by the ferromagnetically aligned Mn spins.

  12. Experimental setup Balancing unit OUT Pump beam (circularly polarized) Band edge exciton absorption spectrum Polarization beam splitter Sample Probe beam (linear polarized) Excitation Laser spectrum

  13. Absorption and Photoluminescence Experimental setup Absorption ・Spectrophotometer Photoluminescence ・Ar-ion laser Excitation ・1/3 meter grating spectrometer and a charge-coupled device

  14. Magnetic Polaron h e E h e Free Exciton Magnetic Polaron (FMP) Mn spin Exciton spin Localization only by sp-d exchange interaction Bound Magnetic Polaron (BMP) Electron or hole localized to impurities, then formation of magnetic polaron

  15. PIFR in Magnetic field To remove the back ground, the PIFR measured with  and  pumping was subtracted 0.25T, 5K The PIFR signal that remain in negative time region is appear Decay time of the signal in FMP resonance is longer than the repetition time of light source (13ns) The exciton life time is no more than 300 pico seconds The photoinduced ferromagnetic alignment of Mn spin by FMP formation

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