Study of optical manipulation of ferromagnetism and spin-based - - PowerPoint PPT Presentation

Semicond emiconductor uctor Nano-S Nano-Spintro pintronics nics

Think and grow Act and test Show and discuss

Outline :

• 1. Why light and spins?
• 2. Manipulation of M without H
• 3. Detection and emission of circular polarization

spin electron charge

Hiro Munekata, Tokyo Tech.

Study of optical manipulation of ferromagnetism and spin-based photonics

light charge

2000 2050 2100 1950

spin

intensity

（heat source）

intensity, wavelength, polarization, phase

（superordinate energy source for I,E,E,B,M applications）

Information, Energy, Environment, Bio, Materials

Range of Applications LIGHT EVERYWHERE high speed selectivity contact less nonlinearity quantum character

Vision

light

electron

multi photons

heat, chemical reaction, etc. Competition with chemical bonds (lattices)

Signals are small and fast-disappearing Ａngular momentum h would be the smallest quantity that would handle physical information.

single photon Linear polarization Circular polarization

• E. Hecht “Optics”, 2nd ed. (1990, Addison-Wesley Publishing Comp., Reading, MA )

μ0H (Tesla) ΔI ≡ I (σ+) − I (σ−) (nA)

Light-induced magnetization In (In,Mn)As (1997 - ) III-V based diluted magnetic semiconductors (1988 - )

(In,Mn)As (Ga,Mn)As etc.

Influence of circular polarization, pulsed excitation; (Ga,Mn)As, (In,Mn)As (2002 - ) Circular polarization detection; diff.-g p-n junction (2003 - ) Spin voltaic effect, InGaAs-AlGaAs Spin-LED, MnSb-GaAs Hybrid optical isolator, (MnSb with InP-based structures)

600 400 200

• 200
• 400
• 600

MO signal [μ degree] 1500 1000 500 Time delay [ps]

• 80
• 70
• 60
• 50
• 40

1537 1538 1539 1540 1541 1542 1543 forward backward

Transmission intensity [dBm] Wavelength [nm]

EC EV

σ− H ≠ 0 g ≠ 0 g = 0 n p

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 ≈ 3μJ cm-2)

x y z

M E

θeff [a. u.] 1000 500 Time delay [ps]

θeff

M ⊥ E

pr

It takes time to change magnetic anisotropy ! Why? Why it tilts toward z direction ?

6 4 2 θ [mrad.] 1000 500 Time delay [ps]

MO signal [a. u.] 130 120 110 100 90 80 70 Magnetic field [Oe]

No pump Δt = 61 ps Δt = 3860 ps Δt = -139 ps (13 ns) Δt = 928 ps With pump

Thermal Heating of Lattice Temperature

Thermal heat ing ~ 1 K τlat t ice >> 13 ns

ΔT

Error bar

A B C

Ec Ev p0 ∼ 1020 cm-3

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.

θeff [a. u.] 1000 500 Time delay [ps]

θeff

Δp ∼ 1015-16 cm-3 t ∼ 50 ps t = 0- 0.2 ps t < 0 ps

A change in hole number at around EF is the key.

• Y. Hashimoto, S. Kobayashi, and H. Munekata, PRL 100, 067202 (08)

t T

∼ 1 K P ≈ 3 μJ cm-2 holes injected holes

EF EF’

YH SK experiment calculation Different from metals !

Dependence of Mn contents on precession of magnetization

θeff [a. u.] 1000 500 Time delay [ps]

θeff

hω = g μ Heff Heff = HMn = Jpd <s>

SK

small x, low p large x, high p

• T. Dietl et. al., Phys. Rev. B 63, 195205 (2001)

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

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.

Spin - Photonics

JH YG MY WT

We began with studying the conversion between circular polarization and spin current.

Ec Ev

σ + and σ − spins

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.

Spin voltaic effect

• I. Zutic,et.al PRL (2002)

Amount of current depends on spin polarization of carriers.

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.

H.Kosaka.et.al. Elecron.Lett.37,464,(2001)

g-factor engineering (Ⅲ-Ⅴ SC )

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.

For = For(↑) + For(↓) Back = Back(↑) + Back(↓) For − Back = {For(↑) − Back(↑)} + {For(↓) − Back(↓)} Δ(σ − − σ +) = {ΔFor(↑) − ΔBack(↑)} − {ΔFor(↓) − ΔBack(↓)} = {ΔFor(↑) − ΔFor(↓)} − {ΔBack(↑) − ΔBack(↓)} ΔFor(↑) = ΔFor(↓). Therefore, we need ΔBack(↑) ≠ ΔBack(↓) to get non-zero Δ. graded g, homo p-n graded g, hetero p-n abrupt Δg, hetero p-n

(β P = 0.7%)

in the end of 2006

• T. Kondo, et.al. JJAP 45, 26.L663 (2006)

⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − Δ − + ⋅ ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + Δ − + ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ Δ − = kT E L D kT E L D kT E

eff e R e eff e R e eff

) ( exp ) ( exp 2 exp ζ ν ζ ν β

P = 30 - 50%

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs. P = 30-50%

Current injection (non-equilibrium condition) and hetero-spin transport factor β

We need ΔBack(↑) ≠ ΔBack(↓) to get non-zero Δ. With carriers flowing forward, EF,p is pushed upward, giving rise to an increase in backward flow. Consequently, hetero-spin transport factor β is increased. ⎜ΔBack(↑) − ΔBack(↓)⎜ is increases..

Effect of hot electrons !

For Back

JH

Spin - Photonics

JH YG MY WT

Extract information from the state of polarization

Ec Ev

σ + and σ − spins Chemical synthesis and analysis

• pharmaceutics
• foods and ingredients

Bio-technology Information processing with quantum

Tok Tokyo Te 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 )

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.

Think and grow Act and test Show and discuss

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.)

Tok Tokyo Te Tech

• ch. Spi

. Spintroni ntronics Labs. s Labs.