Semicond emiconductor uctor Nano-S Nano-Spintro pintronics nics Think and grow Show and discuss Act and test Study of optical manipulation of ferromagnetism and spin-based photonics Hiro Munekata, Tokyo Tech. Outline : spin 1. Why light and spins? 2. Manipulation of M without H charge 3. Detection and emission of circular polarization electron
Vision Information, Energy, Environment, Bio, Materials light Range of Applications LIGHT EVERYWHERE spin high speed selectivity electron contact less charge nonlinearity quantum character light 1950 2000 2050 2100 intensity, wavelength, polarization, phase intensity （ superordinate energy source for I,E,E,B,M applications ） （ heat source ）
Ａ ngular momentum h would be the smallest quantity that would handle physical information. Linear polarization multi photons Circular polarization single photon E. Hecht “Optics”, 2 nd ed. (1990, Addison-Wesley Publishing Comp., Reading, MA ) heat, chemical Competition with chemical bonds (lattices) reaction, etc. Signals are small and fast-disappearing
Circular polarization detection; (In,Mn)As diff.- g p - n junction (2003 - ) (Ga,Mn)As etc. III-V based diluted magnetic Δ I ≡ I ( σ + ) − I ( σ − ) (nA) p n semiconductors (1988 - ) g = 0 g ≠ 0 E C σ − E V Light-induced magnetization H ≠ 0 In (In,Mn)As (1997 - ) μ 0 H (Tesla) Spin voltaic effect, InGaAs-AlGaAs Influence of circular polarization, Spin-LED, MnSb-GaAs pulsed excitation; Hybrid optical isolator, (Ga,Mn)As, (In,Mn)As (2002 - ) (MnSb with InP-based structures) 600 MO signal [ μ degree] Transmission intensity [dBm] -40 400 200 forward -50 backward 0 -200 -60 -400 -600 -70 0 500 1000 1500 Time delay [ps] -80 1537 1538 1539 1540 1541 1542 1543 Wavelength [nm] light-induced precession of M T. Amemiya, et al ., Appl. Phys. Exp. 1 , 022002 (2008).
Photo-induced precession in GaMnAs (P&P, λ = 790nm, P ≈ 3 μ J cm -2 ) E z y M x M ⊥ E pr θ eff [a. u.] θ eff It takes time to change magnetic anisotropy ! Why? 0 0 500 1000 Why it tilts toward z direction ? Time delay [ps]
Thermal Heating of Lattice Temperature A C B No pump With pump MO signal [a. u.] Δ t = 61 ps Δ t = 928 ps Δ t = 3860 ps Δ t = -139 ps (13 ns) 70 80 90 100 110 120 130 θ [mrad.] 6 Error bar Magnetic field [Oe] Δ T 4 2 Thermal heat ing ~ 1 K 0 τ lat t ice >> 13 ns 0 500 1000 Time delay [ps]
Tok Tokyo Te Tech ch. Spi . Spintroni ntronics Labs. s Labs. A change in hole number at around E F is the key. Y. Hashimoto, S. Kobayashi, and H. Munekata, PRL 100 , 067202 (08) θ eff [a. u.] θ eff YH SK T P ≈ 3 μ J cm -2 0 0 500 1000 experiment ∼ 1 K calculation Time delay [ps] t E c t < 0 ps t ∼ 50 ps t = 0- 0.2 ps E v holes E F E F ’ p 0 ∼ 10 20 cm -3 injected holes Δ p ∼ 10 15-16 cm -3 Different from metals !
Dependence of Mn contents on precession of magnetization h ω = g μ H eff θ eff [a. u.] θ eff 0 0 500 1000 Time delay [ps] SK H eff = H Mn = J pd < s > small x , low p large x , high p T. Dietl et. al., Phys. Rev. B 63 , 195205 (2001)
Tokyo Te Tok Tech ch. Spi . Spintroni ntronics Labs. s Labs. Non-thermal influence of pulsed optical excitation on magnetization has been clearly shown. - low power excitation] - a system with free carriers - dynamical change in magnetic anisotropy - spin-orbit interaction Systematic study of an effective magnetic field for Mn spins without an external magnetic field. Coherent control
Tokyo Te Tok Tech ch. Spi . Spintroni ntronics Labs. s Labs. Spin - Photonics WT E c YG JH E v σ + and σ − spins MY We began with studying the conversion between circular polarization and spin current.
Tok Tokyo Te Tech ch. Spi . Spintroni ntronics Labs. s Labs. Spin voltaic effect Amount of current depends on spin polarization of carriers. I. Zutic, et.al PRL (2002)
Tok Tokyo Te Tech ch. Spi . Spintroni ntronics Labs. s Labs. g -factor engineering ( Ⅲ - Ⅴ SC ) H.Kosaka. et.al . Elecron.Lett. 37 ,464,(2001)
Tok Tokyo Te Tech ch. Spi . Spintroni ntronics Labs. s Labs. abrupt Δ g , hetero p - n graded g , homo p - n graded g , hetero p - n For = For( ↑ ) + For( ↓ ) Back = Back( ↑ ) + Back( ↓ ) For − Back = {For( ↑ ) − Back( ↑ )} + {For( ↓ ) − Back( ↓ )} Δ ( σ − − σ + ) = { Δ For( ↑ ) − Δ Back( ↑ )} − { Δ For( ↓ ) − Δ Back( ↓ )} = { Δ For( ↑ ) − Δ For( ↓ )} − { Δ Back( ↑ ) − Δ Back( ↓ )} Δ For( ↑ ) = Δ For( ↓ ). Therefore, we need Δ Back( ↑ ) ≠ Δ Back( ↓ ) to get non-zero Δ .
Tok Tokyo Te Tech ch. Spi . Spintroni ntronics Labs. s Labs. in the end of 2006 ( β P = 0.7%) P = 30-50% P = 30 - 50% − Δ ⎛ ⎞ 2 E ⎜ ⎟ eff exp ⎜ ⎟ ⎝ kT ⎠ β = ⎡ Δ + ζ ⎤ ⎡ Δ − ζ ⎤ ⎛ ⎞ ⎛ ⎞ ( E ) ( E ) D D ⎜ ⎟ ⎜ ⎟ + − eff ⋅ + − eff ⎢ e ⎥ ⎢ e ⎥ exp exp ⎜ ⎟ ⎜ ⎟ ν ν ⎢ ⎥ ⎢ ⎥ ⎝ ⎠ ⎝ ⎠ ⎣ L kT ⎦ ⎣ L kT ⎦ R e R e T. Kondo, et.al. JJAP 45 , 26.L663 (2006 )
Current injection (non-equilibrium condition) and hetero-spin transport factor β We need Δ Back( ↑ ) ≠ Δ Back( ↓ ) to get non-zero Δ . With carriers flowing forward, E F,p is pushed upward, giving rise to an increase in backward flow. Consequently, hetero-spin transport factor β is increased. ⎜Δ Back( ↑ ) − Δ Back( ↓ ) ⎜ is increases.. For Back Effect of hot electrons ! JH
Tokyo Te Tok Tech ch. Spi . Spintroni ntronics Labs. s Labs. Spin - Photonics E c WT YG E v JH σ + and σ − spins Extract information from the state of polarization MY Chemical synthesis and analysis - pharmaceutics - foods and ingredients Bio-technology Information processing with quantum
Tokyo Te Tok Tech ch. Spi . Spintroni ntronics Labs. s Labs. Diffusion is great ! ( Depletion region would not cause problems) Hot carriers help spin transport across heterojunction ! ( Dynamic enhancement of β )
Tokyo Te Tok Tech ch. Spi . Spintroni ntronics Labs. s Labs. Think and grow Show and discuss Act and test Summary : 1. precession induced by the optical excitation (non-thermal effect, insight into f.m.s.c) 2. spin transport in SC (diffusion, heterojunctions) Co-workers Y. Kitamoto (associate professor, Tokyo Tech.) S. Sugahara (associate professor, Tokyo Tech.) Y. Hashimoto (research scientist, Tokyo Tech.) J. Hayafuji and S. Kobayashi (doctor course students, Tokyo Tech.)
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