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FEMTO 2008
DYNAMIQUE DE SPIN DANS LES STRUCTURES SEMICONDUCTRICES
Xavier MARIE*Laboratoire de Physique et Chimie des Nano-Objets , Toulouse
(INSA-CNRS-UPS)* Institut Universitaire de France
@ Mc Caffey
FEMTO 2008, FEMTO 2008, MittelwihrMittelwihr
FEMTO 2008
Un peu d’histoire…
�Enhancement of Nuclear Magnetic Resonance obtainedby optical pumping in Silicon (irradiation time with Xe lamp : ~20 hours)
SpinOptics
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Ecole Polytechnique
George Lampel, PhD thesis
Paris 1968
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Un peu d’histoire…
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ElectronCharge (-e)
Spin ↑↑↑↑, ↓↓↓↓
Applications potentielles? : Transistors de spin (Spin-FET)Optoélectronique polarisé (Spin-LED, Spin-Laser) Mémoire de spin à un électron Information quantique…
Objectifs :
• Génération de porteurs polarisés en spin• Transport de spin• Manipulation/Contrôle des propriétés de spin• Détection efficace de la polarisation de spin
Electronique de spin et semiconducteurs ?
FEMTO 2008
Outline…
I. Principles of Optical orientation experiments1. History2. Optical selection rules3. Electron spin polarization in bulk GaAs
II. Experimental optical techniques for measuring the spin properties1. Stationnary photoluminescence (B≠0 and B=0)2. Time-resolved photoluminescence3. Time-resolved differential transmission4. Time-resolved Faraday/Kerr rotation5. Experiments to measure optically spin transport
III. Spin Dynamics in semiconductor Quantum Dots
FEMTO 2008
Structure de bande d’un semiconducteur à gap direct
III-V and II-VI Zinc-blende semiconductors
GaAs : Td symmetryTypical values : GaAs Eg~1.52 eV , ∆so ∼0,34 eV (T=4 K)
*G. Fishman, PhD thesis (Orsay 1974)
Analogy with atoms*
L=0, S=1/2 J=1/2 (CB)
J=3/2 (HH,LH)
L=1, S=1/2
J=1/2 (SO)
Jz±1/2
±3/2
±1/2
±1/2
FEMTO 2008
Electrons (CB)
HH,LH (VB)
GaAs, K=0
|-1/2> |1/2>sz
j z |3/2> |1/2>
History : G. Lampel, PRL 10,1968 : SiR. Parsons, PRL 23, 1969 : GaSbEkimov ,Safarov, JETP Lett 12, 293 (1970) : AlGaAsB. Zakharchenya, JETP 13, 1971 : GaAs
σ+σ+σ+σ+
oz
Optical spin orientation in semiconductors
s=1/2
j=3/2
j=1/2 SO (VB)|-1/2>|1/2>
|-3/2>|-1/2>
σσσσ++++
(3) (1)
σσσσ++++
σσσσ++++
(2)Eg
∆so
(1)
σσσσ−−−−
σσσσ−−−−
σσσσ−−−−
(3)(2)
j z
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Value of the spin polarization ?
Electrons (CB)
HH,LH (VB)
|-1/2> |1/2>sz
j z |3/2> |1/2>
s=1/2
j=3/2|-3/2>|-1/2>
Eg
Classical configuration for optical orientation :
gsog EE ≥ω≥∆+ h
σσσσ++++
(3) (1)
σσσσ++++
↓ ↑↓↓
Electron spin polarization in bulk GaAs : P s=- 50%
σ+σ+σ+σ+
oz
FEMTO 2008
Outline…
I. Principles of Optical orientation experiments1. History2. Optical selection rules3. Electron spin polarization in bulk GaAs
II. Experimental optical techniques for measuring the spin properties1. Stationnary photoluminescence (B≠0 and B=0)2. Time-resolved photoluminescence3. Time-resolved differential transmission4. Time-resolved Faraday/Kerr rotation5. Experiments to measure optically spin transport
III. Spin Dynamics in semiconductor Quantum Dots
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesa- cw Photoluminescence (1/2)
σ+σ+σ+σ+
oz
I+(-)
Acquisition
Ti : Saphir
Detector
Argon
Chopper
Lock-inFiltre
Mono-chromator
Sample
Pre-amplifier
λ/4 λ/4 λ/4 λ/4 plate
λ/4 λ/4 λ/4 λ/4 platePolarizer
Circular polarization : Pc=(I+-I-)/(I++I-)
Luminescence Intensity I +, I-
1,555 1,560 1,565 1,570 1,575 1,580
t=76 ps
TL=10 K
PE=1
Energie de détection (eV)
Inte
nsité
0,0
0,2
0,4
0,6
0,8
Polarisation circulaire
I+
I-
Detection Energy (eV)
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Experimental techniques to study optically the spin p ropertiesa- cw Photoluminescence (2/2)
s
ss
PP
ττ+
=1
)0( Ps(0) : initial spin polarization (~-50% for bulk GaAs)τ : electron lifetimeτs : electron spin relaxation time
Steady state electron spin polarization :σ+σ+σ+σ+
oz
I+(-)
Theory : τ/τs=0
Experiment
Ekimov, Safarov, Zh Eksp Teor Fiz Pisma 13, 700 (1971)GaAs, T=1,7 K
Pc
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesa- cw Photoluminescence (3/5)
yx
z
Bx
hhνννννννν (σ (σ (σ (σ (σ (σ (σ (σ −−−−−−−−))))))))
SSzz
t = 0
+1/2
t =π/ω
-1/2
Magnetic field axis of spin orientation (Voigt configuration) : Bx oz⊥ ⊥
Spin precession with Larmor frequency :
Bg Bµ=ωhg : electron g-factorµΒ : Bohr magneton
Cw excitation and detection :Decrease of the spin polarization Sz with B
� Pcirc decreases if B increases (Hanle curve*)* Hanle, Z. Phys. 30, 93 (1924) Depolarization of the resonance fluorescence in gasesParsons, PRL 23, 1152 (1969)Hanle effect in semiconductor (GaSb)
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesa- cw Photoluminescence (4/5)
B
hhνννννννν(σ (σ (σ (σ (σ (σ (σ (σ −−−−−−−−))))))))
SSzz
1/Ts=1/τ+1/τs : effective spin lifetime
If during the electron lifetime, the electron spin makes many revolutions, then in stationary conditions <Sz> will vanish
( )21
)0()(
s
ss
T
BPBP
ω+==
Hanle curve : Lorentzian
( )21
)0()(
s
zz
T
SBS
ω+=
Equation of motion of average electron spin in B :
τ−−
τ−ω= 0SSS
xSdtdS
s
Putting dS/dt=0 and , we find :0S⊥ω
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesa- cw Photoluminescence (5/5)
B
hhνννννννν(σ (σ (σ (σ (σ (σ (σ (σ −−−−−−−−))))))))
SSzz
1/Ts=1/τ+1/τs : effective spin lifetime
( )21
)0()(
s
ss
T
BPBP
ω+==
Hanle curve : Lorentzian
( )21
)0()(
s
zz
T
SBS
ω+=
Parsons, PRL 23, 1152 (1969)
GaSb
Dyakonov et al., ICPS XII, p771(1974)Kalevich et al., Sov. Phys. Solid St. 23, 892 (1981)
B(kG)
)0(
)(
SBS GaAlAs
Parameters : ω, Τs g, τ, τs
FEMTO 2008
Outline…
I. Principles of Optical orientation experiments1. History2. Optical selection rules3. Electron spin polarization in bulk GaAs
II. Experimental optical techniques for measuring the spin properties1. Stationnary photoluminescence (B≠0 and B=0)2. Time-resolved photoluminescence3. Time-resolved differential transmission4. Time-resolved Faraday/Kerr rotation5. Experiments to measure optically spin transport
III. Spin Dynamics in semiconductor Quantum Dots
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesb- Time-resolved Photoluminescence (1/3)
Mode locked Laser
photodiode
Spectrometer
StreakCamera
Acquisition
Sampleλ/4 λ/4 λ/4 λ/4 plate Polarizer
λ/4 λ/4 λ/4 λ/4 plate
Time-resolved PL with an ultrafast camera
1050 1100 1150 12000
10
20
30
40
50
60
70
80
Inte
nsité
(u.a
.)
λλλλ (nm)
Energie
Tem
ps
1050 1100 1150 12000
10
20
30
40
50
60
70
80
Inte
nsité
(u.a
.)
λλλλ (nm)
Energie
Tem
ps
Time-resolved polarized photoluminescenceTime (ps)
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Spectroscopie de Photoluminescence par Spectroscopie de Photoluminescence par mméélange de frlange de fr ééquences quences àà 1 couleur1 couleur
Monochromateur PM
échantillon
Ti:Saphir
LiIO3
Pilotage & Acquisition
impulsion excitatrice
luminescence
retardimpulsionretardée
0 100 200 300 400
Temps (ps)
Inte
nsité
-0,2
0,0
0,2
0,4
0,6
0,8
1,0
détection : 1,568 eV
TL=10 K
PE=1
Polarisation circulaire
I+
I-
T. Amand , X. MarieFemtosecond laser pulsesEd. C. Rulliere, Springer (2002)
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|-1/2> |1/2>sz
j z |3/2> |1/2>
s=1/2
j=3/2|-3/2>|-1/2>
σσσσ++++
(3) (1)
σσσσ++++
↓ ↑↓↓ (1) (3)
σσσσ−−−−σσσσ−−−−
h
sτ
e
sτ
Hole spin relaxation time: ~4 psElectron spin relaxation time : ~ 2000 ps
hsτ
esτ
GaAs,T=1,7 K
Marie et al., ICPS 24, Jerusalem 1255 (1998)
Circular polarization of luminescence :100% � 25 % � 0
hsτ e
sτ
Hole spin relaxation (bulk)
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Experimental techniques to study optically the spin p ropertiesb- Time-resolved Photoluminescence (2/3)
Spin quantum beats experiments (B≠0)
ω=gµBB/h.
Oscillation of the circularly-polarizedI+(-) luminescence components withthe pulsation :
�measurement of g-factor
|g|=0,39 ; GaAs/AlGaAs quantum wellW. Ruhle, Max Planck, StuttgartHeberle et al., PRL 72, 3888(1994)
B
hhνννννννν(σ (σ (σ (σ (σ (σ (σ (σ −−−−−−−−))))))))
SSzz
yx
z
Magnetic field axis of spin orientation(Voigt configuration) : Bx oz
⊥⊥
Spin precession with Larmor frequency :
Bg Bµ=ωhg : electron g-factorµΒ : Bohr magneton
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesb- Time-resolved Photoluminescence (3/3)
Spin quantum beats experiments (B≠0)
|0>
hωab
Laser pulse σ−
Ea Eb
B≠0
ω=gµBB/h.
ba β+α=ΨExcitation of a coherent superposition :
Temporal evolution of this state :Observation of quantum beats
Electron spin quantum beats :
Oscillation of the circularly-polarizedI+(-) luminescence components with the pulsation :
Spin coherence > 500 psW. Ruhle, Max Planck, StuttgartHeberle et al., PRL 72, 3888(1994)
↓+↑=a
↓−↑=b
FEMTO 2008
Outline…
I. Principles of Optical orientation experiments1. History2. Optical selection rules3. Electron spin polarization in bulk GaAs
II. Experimental optical techniques for measuring the spin properties1. Stationnary photoluminescence (B≠0 and B=0)2. Time-resolved photoluminescence3. Time-resolved differential transmission4. Time-resolved Faraday/Kerr rotation5. Experiments to measure optically spin transport
III. Spin Dynamics in semiconductor Quantum Dots
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesc - Time-resolved Differential Transmission
Hilton et al, PRL 89 (2002)Hole spin in GaAs QW : Ostanickiet al, PRB 75 (2007)Exciton spin in GaN : Brimontet al, Phys. Rev. B 77 (2008)
Technique Pompe-Sonde : - Pompe polarisée circulairement σ+- Sonde polarisée linéairement σx
Si les porteurs créés par la pompe ont conservé leur orientation de spin, la polarisation de la sonde va être elliptique.
���� Relaxation de spin du trou : 110 fs (GaAs, T=300 K)
Pompe Ti:Sa 90 fsSonde : idler OPO
(Pompe)
(Sonde)
FEMTO 2008
Outline…
I. Principles of Optical orientation experiments1. History2. Optical selection rules3. Electron spin polarization in bulk GaAs
II. Experimental optical techniques for measuring the spin properties1. Stationnary photoluminescence (B≠0 and B=0)2. Time-resolved photoluminescence3. Time-resolved differential transmission4. Time-resolved Faraday/Kerr rotation5. Experiments to measure optically spin transport
III. Spin Dynamics in semiconductor Quantum Dots
FEMTO 2008
Experimental techniques to study optically the spin p ropertiesd - Time-resolved Faraday (Kerr) rotation (2/6)
Pump-probe Faraday rotation dynamics
D. Awschalom, Santa BarbaraBaumberg et al., PRL 72, 712 (1994)Kikkawa et al., PRL 80, 4313 (1998)
FEMTO 2008
Electric field tuning of the electron g factor(Electrical control of spin coherent precession in a q uantum well)
Salis et al., Nature 414, 619 (2001)
Electron Landé g factor (bulk) :GaAs, g=-0,44Al0,3Ga0.7As : g=+0,4
Change of the beat period asa function of the bias (fixed B=6 T)
Bias dependence change of the g factor due to variation of electron wavefunction penetration in the barrier
Faraday Rotation Dynamics :
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Experimental techniques to study optically the spin p ropertiesd - Time-resolved Faraday (Kerr) rotation (1/4)
R.T. Harley, SouthamptonWorsley et al., PRL 76, 3224 (1996)D. Awschalom, Santa BarbaraKikkawa et al., Science 277, 1284(1997)
• ∆θ (t) ~ <Sz>(t)
• Time resolution ~ pulse width• Sensitivity up to 1:10 6
Pump-probe Kerr rotation dynamics
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Experimental techniques to study optically the spin p ropertiesd - Time-resolved Kerr rotation (2/4)
D. Scalbert, MontpellierCamilleri et al., PRB 64, 85331 (2001)D. Awschalom, Santa BarbaraCrooker et al., PRL 77, 2814 (1996)
Pump-probe Kerr rotation dynamicsin diluted magnetic II-VI heterostructures(CdMnTe quantum wells)
FEMTO 2008
Outline…
I. Principles of Optical orientation experiments1. History2. Optical selection rules3. Electron spin polarization in bulk GaAs
II. Experimental optical techniques for measuring the spin properties1. Stationnary photoluminescence (B≠0 and B=0)2. Time-resolved photoluminescence3. Time-resolved differential transmission4. Time-resolved Faraday/Kerr rotation5. Experiments to measure optically spin transport
III. Spin Dynamics in semiconductor Quantum Dots
FEMTO 2008
Spin transport in undoped GaAs
Spin transport in GaAs over a distance of 4 µµµµm and E~6 kV/cm (T=10 K)Electron spin polarization created and detected optically :
- t=0 : excitation withσ+ picosecond pulse- Detection : time-resolved photoluminescence
Hägele et al., APL 73, 1580 (1998)
N(z)
z(µm)
zeNzN α−= ).0()(1410: −≈α cmtcoefficienabsorption
~1 µµµµm
t=0 : Optical generation
Time-resolved PL of the InGaAsprobe quantum well
Polarization ~ 35 %
I+
FEMTO 2008
Outline…
I. Principles of Optical orientation experiments1. History2. Optical selection rules3. Electron spin polarization in bulk GaAs
II. Experimental optical techniques for measuring the spin properties1. Stationnary photoluminescence (B≠0 and B=0)2. Time-resolved photoluminescence3. Time-resolved differential transmission4. Time-resolved Faraday/Kerr rotation5. Experiments to measure optically spin transport
III. Spin Dynamics in semiconductor Quantum Dots
FEMTO 2008
Quantum Welle.g. : A = GaAs
B = AlGaAs
Nanostructures Nanostructures semiconductricessemiconductrices
EG(B) EG(A)
Conduction band
Valenceband
(b) Energy
LA
(a)
LA
BAB
(a)
a
BV
BC
∆∆∆∆so
EG
k
Energie
HH
LH
SO
(b)
a : lattice parameter
zinc blendeelementary cell
Growth axis
hhlh
E
D(E)
E
D(E)
E
D(E)
3D 2D 1D 0D
E
D(E)
(a) Bulk (b)Quantum well
(c) Quantum wire
(d)Quantum dot Boîtes quantiques
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Croissance Stransky-Krastanov
BOITES QUANTIQUES AUTO-ORGANISEES InAs/GaAs
WettingLayer 3D
Island
(a) (b) (c)
InAs
GaAs
Désaccord de maille InAs/GaAs : ~7 %
TEM Images (Y. Musikhin, IOFFE Institute)
nm
Épitaxie à jets moléculaires (LAAS)
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EtatsEtatsElectroniquesElectroniquesdansdansles les boboîîtestesquantiquesquantiques
GaAs barrier (3D states)
Wetting layer (2D states)
Excited levels
CB ground stateDiscrete energylevels
Conduction states
Valence states
E
s, p… : carrier envelope orbital
state
D(E)
cp
cs
vs
vp
Microscopie Electronique en Transmission A. Ponchet CEMES, Toulouse (95)
GaAs
GaAsInAs
20 nm
FEMTO 2008
GaAs barrier (3D states)
Wetting layer (2D states)
Excited levels
CB ground stateDiscrete energylevels
Conduction states
Valence states
cp
cs
vs
vp
EtatsEtatsElectroniquesElectroniquesdansdansles les boboîîtestesquantiquesquantiques
Photoluminescence(Boîte unique)
Energy (eV)
-
+
laser
1.0 1.1 1.2 1.3 1.4
30 W.cm-2
150 W.cm-2
900 W.cm-2
Etats excités
Etat fondamental
Inte
nsité
(un
ité a
rb.)
Energie (eV)
Spectroscopie stationnaire
1.0 1.1 1.2 1.3 1.4
30 W.cm-2
150 W.cm-2
900 W.cm-2
Etats excités
Etat fondamental
Inte
nsité
(un
ité a
rb.)
Energie (eV)
Spectroscopie stationnaire
Energy ((((eVeVeVeV))))
Inte
nsity
(arb
. Uni
ts)
vc ss−
vc pp−
vc dd−
1.0 1.1 1.2 1.3 1.4
30 W.cm-2
150 W.cm-2
900 W.cm-2
Etats excités
Etat fondamental
Inte
nsité
(un
ité a
rb.)
Energie (eV)
Spectroscopie stationnaire
1.0 1.1 1.2 1.3 1.4
30 W.cm-2
150 W.cm-2
900 W.cm-2
Etats excités
Etat fondamental
Inte
nsité
(un
ité a
rb.)
Energie (eV)
Spectroscopie stationnaire
Energy ((((eVeVeVeV))))
Inte
nsity
(arb
. Uni
ts)
vc ss−
vc ss−
vc pp−
vc pp−
vc dd−
vc dd−
Photoluminescence(ensemble de boîtes)
FEMTO 2008
POMPAGE OPTIQUE ORIENTE
Electrons (CB)
HH (VB) K=0
|-1/2> |1/2>sz
j z |3/2> |-3/2>
σσσσ++++ σσσσ−−−−
(((( ))))2
11X
−−−−++++====
(((( ))))2i
11Y
−−−−−−−−====
0
Excitation Linéaire
σσσσX σσσσY
Excitation Circulaire
2/1,2/31 −−−−==== 2/1,2/31 −−−−====−−−−
σσσσ++++ σσσσ−−−−
0
σ+σ+σ+σ+
oz
2D EXCITONS Jz=j z+sz+
-
G. Lampel, PRL 10,1968Zakharchenya, JETP 13, 1971
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GaAs barrière
Couche de mouillage
Etats de Conduction
Etats de Valence
Excitation strictement résonante de boîte quantique
ps laser
cs
vs
FEMTO 2008
Spectroscopie de photoluminescence résolue en temps( picoseconde, sub-picoseconde)
Mélange de fréquence (une ou deux couleurs) Synchro-scan Streak Camera
Dispositifs expérimentaux.
FEMTO 2008
MMéélange de frlange de frééquences quences àà 2 couleurs2 couleurs
MonochromatorPM
NLCrystalLiIO 3
Sample
Ti:SaAr+
OPO
1.5 ps or 150 fs
OpticalParametricOscillator
~1150 nm~800 nm
~470 nm
M. Paillard et al., APL 76 (2000)
FEMTO 2008
Excitation Excitation rr éésonantesonantede de boboîîtete((spectroscopiespectroscopiede photoluminescence) de photoluminescence)
Pas de déclin mesurable ! : ττττs> 20 ns Ni le spin , ni le spin du trou ne relaxent à l’échelledu temps de vie radiatif
Paillard et al,, PRL 86, 1634 (2001); Cortezet al, PRL. 89, 207401(2002) ; Laurent et al, PRL 94, 147401 (2005); Braun et al, PRL 94, 116601 (2005) ; Nature, Research Highlights, Vol. 434, 839 (2005)
0 500 1000 1500 2000 2500
Inte
nsity
(ar
b. u
nits
)
Time (ps)
0.0
0.2
0.4
0.6
0.8
1.0
IY
IX
Linear Polarization
Excitation σX
• Photogeneration d’excitons linéaires
• Forte polarisation linéaire
T=10 K
75.0≅+−=
YX
YX
L II
IIP
( ) 2/,2/3,2/3 ↑+↓=X
ps laser
cs
vs
BC
BV
FEMTO 2008
Relaxation du spin d’exciton dans des puits quantiques GaAs/AlGaAs
0 2 0 4 0 6 0
0 .0
0 .5
1 .0
T IM E (p s )
L in ea r ex c ita t io n 1 09c m -2
5 x 1 09
2 x 1 01 0
0 2 0 4 0 6 0 8 0
0 .0
0 .5
1 .0C irc u la r ( σσσσ + ) e x c ita t io n 3 x 1 08cm -2
4 x 1 09
6 x 1 09
EXCITATION RESONANTE :Ts1 ~50 -100 ps
• Bar-Ad et al., PRL 68 (1992)
• Vinattieri et al., PRB 50 (1994)
• Amand et al., PRL 78 (1997) ...
Ts2~ 20 -50 ps• Worsley et al., PRL 76 (1996)
• Marie et al., PRL 79 (1997) …
AlGaAsGaAsAlGaAs
~5 nm
Po
laris
atio
n
FEMTO 2008
ps laser(σ+)(σ+)(σ+)(σ+)
sc
sv
sc
sv
Charged X+
~ 1 resident hole/QD
Electron spin coherence in transverse magnetic field
B
hhνννννννν(σ (σ (σ (σ (σ (σ (σ (σ ++++++++))))))))
SSzz
Sz
B Spin precession with Larmor frequency :
Bg Be µω ⊥=h
Lombez et al, PRB 75,195314(2007)
FEMTO 2008
Single Dot Optical Spectroscopy
SPAD
Ti/Sapicosecond
Confocal Microscope
B = 0 - 13 TT= 2-300 K
Moteurs piézo
Boîte InAs/GaAs
20 nm
0 1 2 3
Inte
nsité
Temps (ns)
0,1
1
10
100SPIN DYNAMICS OF A SINGLE DOT
I-
I+ BZ=2T
Polarisation C
irculaire (%)
Bz= 4 T
FEMTO 2008
Hyperfine Interaction between electron spins and nuclear spins
Optical Pumping of nuclear spins in a Single Dot
Eble et al, PRB Rapid Com 74, 81306 (2006)Braun et al., PRB 74, 254306 (2006) Urbaszeket al, PRB76 (R), (2007)
Braun et al, PRL 94, 116601 (2005) Pettaet al, Science 309, 2180(2005)Greilichet al,Science 313, 341(2006)
Decoherence time ~1 ns*2T
FEMTO 2008
Problème de la température sur boîtes InAs/GaAs
0 500 1000 1500 2000 25000.01
0.1
1
10K 30K 40K 50K 60K 70K 80K
Lin
ear
Pol
ariz
atio
nTime (ps)
Tim
e d
eca
y
1/kT
Sh
Ph∆Ε∆Ε∆Ε∆Ε
Solutions : Boites GaN , ZnO ? - Boites GaN/AlN- ZnO
FEMTO 2008
Dynamique de spin dans GaN
Spectroscopie pompe-sonde (réflectivité différentielle)
Temps de relaxation de spin du trou : 5 psde l’électron : 15 ps
Brimont et al, PRB 77, 125201(2008)
Delay (ps)
FEMTO 2008
Dynamique de spin dans les boites quantiques GaN/AlN
12 nm
1-2 nm
� Dot size
Martinez-Guerrero, APL 77, 809 (2000)
GaN massif Wurzite, t ~1 ps, Brimont et al, PRB 77, 125201(2008)
Lagarde et al., PRB 77, 041304(R) (2008)
0 100 200 3000 200 400 600 8000
10
20
30
20 K
150 K
(a)
300K
Line
ar
pola
riza
tion
(%)
Time (ps)
(b)
T (K)Temps de relaxation de la polarisation> 10 ns, même à 300 K !
FEMTO 2008
Dynamique de spin dans ZnO
Relaxation de spin du trou dans Zno Massif : ~300 psLagarde et al, PRB 79, 33203 (2008)
Temps de cohérence de spin d’électron ~25 ns (T=300 K)
FEMTO 2008
Spin Laser…
VCSEL :Vertical Cavity Surface Emitting Laser
Reduced laser thresholdAPL 82, 4516 (2003)
Optical pumping
Circularly polarizedunpolarized
|-1/2> |1/2>
|3/2> |1/2> |-3/2>|-1/2>
σσσσ++++(3) (1)
σσσσ++++
↓ ↑↓↓
Réduction du courant de seuil d’un laser par pompage optique d’électrons polarisés en spin
FEMTO 2008
Spin Laser…
VCSEL :Vertical Cavity Surface Emitting Laser
|-1/2> |1/2>
|3/2> |1/2> |-3/2>|-1/2>
σσσσ++++(3) (1)
σσσσ++++
↓ ↑↓↓
M. Oestreich, University of Hannover
Pulsed laser emission synchronized to electron precessionHallstein et al., PRB56, R7076 (1997)
B
hhνννννννν(σ (σ (σ (σ (σ (σ (σ (σ −−−−−−−−))))))))
SSzz
FEMTO 2008
SPIN- LASER
FEMTO 2008
Acknowledgements :Acknowledgements :
CoCo--workers in Toulouse :workers in Toulouse :
Quantum Quantum OptoOpto--electronic group, INSA :electronic group, INSA :
• T. Amand• B. Urbaszek
Collaborations :Collaborations :• O. Krebs, P. Voisin, A. Lemaître, LPN (Marcoussis)
• R. Mattana, H. Jaffrès, J.-M. George, CNRS-Thales (Palaiseau)• P. Gallo, A. Arnoult, C. Fontaine, LAAS (Toulouse)• H. Mariette, S. Founta, J.M. Gérard, Inst. Néel/CEA (Grenoble)• C. Testelin, B. Eble, M. Chamarro, INSP (Paris)
• K. Kavokin, V. Kalevich, Ioffe Institute (St Petersburg)
• T. Kuroda , NIMS (Tsukuba)
• H. Carrère• P. Renucci• A. Balocchi
• C.M Simon• D. Lagarde• T. Belhadj• F. Zhao
