L.Besombes Y.Leger H. Boukari D.Ferrand H.Mariette J. Fernandez- Rossier CEA-CNRS team «...
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![Page 1: L.Besombes Y.Leger H. Boukari D.Ferrand H.Mariette J. Fernandez- Rossier CEA-CNRS team « Nanophysique et Semi-conducteurs » Institut Néel, CNRS Grenoble,](https://reader038.fdocuments.us/reader038/viewer/2022110323/56649d5d5503460f94a3cb16/html5/thumbnails/1.jpg)
L.BesombesY.Leger H. Boukari D.FerrandH.Mariette
J. Fernandez-Rossier
CEA-CNRS team « Nanophysique et Semi-conducteurs »
Institut Néel, CNRS Grenoble, FRANCE
Department of applied physics, University of Alicante, SPAIN
Optical control of an individual spin
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Introduction
Ultimate semiconductor spintronic device: Single magnetic ion / individual carriers
-Control of the interaction between a single magnetic atom and an individual carrier.(spin injection, spin transfer)
-Manipulation of an individual spin (memory, quantum computing)
II-VI Semi-Magnetic semiconductor QDs
Localized carriers
Magnetic doping (Mn: S=5/2)
…Towards a single spin memory.
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Theoretical proposals
Transport: A single QD containing a Mn atom could be use as a spin filter
Nano-magnetism : electrical control of the magnetism.
Hawrylak et al. Phys. Rev. Lett. 95, 217206 (2005)
Qu et al. Phys. Rev. B74, 25308 (2006)
Memories : writing and reading of the spin state of a single Mn atom.
A.O. Govorov et al., Phys. Rev. B 71, 035338 (2005)
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1. Probing the spin state of a single Magnetic atom - II-VI magnetic self assembled QDs - Carriers-Mn exchange interaction - Importance of QD structural parameters on the spin detection (Shape anisotropy, valence band mixing)
2. Carrier controlled Mn spin splitting
- Anisotropy of the hole-Mn interaction - Charge tunable Mn-doped QDs
3. Carriers and Mn spin dynamics
Outline
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UHV-AFM image of CdTe QDs on ZnTe.UHV-AFM image of CdTe QDs on ZnTe.
QDs density: 5.109 cm-2
Size: d=15nm, h=3nm(Lz<<Lx,Ly)
TEM image of CdTe QDs on ZnTe.TEM image of CdTe QDs on ZnTe.
Individual CdTe/ZnTe QDs
1950 2000 2050 2100
d 0,25 m
d 0,5 m
d 20 m
6,5 MLs
PL
Int
ensi
ty (
arb.
uni
ts)
Energy (meV)
meV50
eV50
100 m
Micro-spectroscopy.Micro-spectroscopy.
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Jz=+1
Jz= -1
Jz= - 2
Jz= +2
G.S.
B=0 B=0
eh
eh
- +
meV10
e: spin 1/2h: anisotropic (Jz=3/2)
Jz= -3/2
Jz= -1/2
Jz= +3/2
Jz= +1/2
Sz= +1/2Sz= -1/2
+ -
e
hh
lh
Optical selection rules:
z
Optical transitions in an individual QD
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Electrical control of the charge.
Transfer of holes from the surface states: p type doping of the QDs.
V
p-ZnTe
CdTe
Gated charged quantum dots
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Te
Cd
Mn
•Mn remplace Cd: Mn2+
•Mn2+ S=5/2, 2S+1=6
Cd: 3d10 4s2
Mn: 3d5 4s2
Exchange interaction:
•Mn - electron
•Mn - hole
)x (SMJ IeI
Ie
I
IhIh )x(SMJ
Mn doped II-VI QDs
Electron: σ = 1/2
Hole: jZ = ±3/2
Mn atom: S = 5/2
nm
nm
h
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The presence of a single magnetic atom completely control the emission structure.
Measurement of the exchange interaction energy of the electron, hole, Mn
Phys Rev Lett. 93, 207403 (2004)
Emission of Mn-doped individual QDs
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2zJ
1zJ
X X+Mn2+
Sz = ±5/2, ±3/2, ±1/2
Mn2+
-5/2Jz = -1eh Jz = +1
eh
-3/2
-1/2
+1/2
+3/2
+5/2Jz = -1eh
+5/2
+3/2
+1/2
-1/2
-3/2
-5/2
Exchange constant: s-d, >0p-d, <0
Jz = +1eh
Heavy holeexciton
))S.jS.j(2/1S.j(I
))S.S.(2/1S.(I
zzMnh
zzMne
Mn2+
Heavy-hole exciton / Mn exchange coupling
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2zJ
1zJ
X X+Mn2+
Heavy holeexciton
))S.jS.j(2/1S.j(I
))S.S.(2/1S.(I
zzMnh
zzMne
Mn2+
-
-5/2
+5/2
…
+
+5/2
-5/2
…
1 photon (energy, polar) = 1 Mn spin projection
Overall splitting controlled by Ie-Mn and Ih-Mn .
Heavy-hole exciton / Mn exchange coupling
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Magnetic field dependent PL intensity distribution.
NMn=0 NMn=1
Mn-doped individual QDs under magnetic field
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eh Mn2+
eh
Mn2+
eh Mn2+
Mn2+
B
eh Mn2+
+-
B
Jz = -1 Jz = +1
gMn=2
Mn spin conservation
Mn spin polarization
Boltzmann distribution of the Mn-Exciton system:
latticeeff TT
K5TLatt
Teff=12K
Polarization of the Mn spin distribution
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Resonant excitation
Complex excited states fine structure
Selection of Mn spin distributionand
spin conservation during the lifetime of the exciton.
Statistic Mn spin distribution
B=0T
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S.I Mne
j.I he
zzBhzzBe BjμgBσμg
2B
zzMnh .Sj I
zzBMn BSμg
-1 0 1 2
Energy (meV)
Th.Exp. Effective spin Hamiltonian:
Carriers-Mn exchange coupling
- X-Mn Overlap- QD shape- Strain distribution
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Ie-Mn in a flat parabolic potential:
26nmd
3nmLz
Exchange integrals controlled by the overlap with the Mn atom.
Decrease ofX-Mn overlap
1.3 meV
Detection condition: Exciton-Mn overlap
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Influence of the QD shape
Phys Rev Lett. 95, 047403 (2005)
Influence of the valenceband mixing
Jz=+ - 3/2
Jz=+ - 1/2
Sz= +- 1/2 e
hhlh
Phys Rev B. 72, 241309(R) (2005)
QD3QD1 QD2
Heavy-hole + Mn
Detection condition: Structural parameters
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Inhomogeneous relaxation of strain in a strained induced QD (Bir & Pikus Hamiltonian):
0.. SjSjIMnh
|3/2> |1/2> |-1/2> |-3/2>
|3/2> = c1 |3/2>+ c2 |-1/2> c1>>c2
|-3/2> = c3 |-3/2>+ c4 |1/2> c3>>c4
~
~
<3/2| j - |-3/2> = 0~ ~ via cross components because
12
3,
2
3
13
10
3
2
2
1,
2
3
k
E
Valence band mixing in strained induced QDs
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Allows simultaneous hole-Mn spin flip
Possibility to flipfrom jz= +3/2 to -/3/2 via light holes
Effective h-Mn interaction term in the Heavy hole Subspace
eh
eh
lh : Heavy-light hole
mixing efficiency
))..(.( SjSjSjIlhzzMnh
2zJ
1zJ
X X+Mn2+
~~
Influence of valence band mixing
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Allows simultaneous hole-Mn spin flip
Effective h-Mn interaction term in the Heavy hole Subspace
eh
eh
lh : Heavy-light hole
mixing efficiency
))..(.( SjSjSjIlhzzMnh Exp.
Th.
Emission of “non-radiative” exciton states
Possibility to flipfrom jz= +3/2 to -/3/2 via light holes
~~
Phys Rev B. 72, 241309(R) (2005)
Influence of valence band mixing
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X-Mn in transverse B field«0»
B//
Faraday
B┴
Voigt
Voigt: Complex fine structure…Suppression of the hole Mn exchange interaction
Faraday:Zero field structure is conserved
001
001
«+1 »«-1 »
Phys Rev B. 72, 241309(R) (2005)
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1. Probing the spin state of a single Magnetic atom - II-VI magnetic self assembled QDs - Carriers-Mn exchange interaction - Importance of QD structural parameters on the spin detection (Shape anisotropy, valence band mixing)
2. Carrier controlled Mn spin splitting
- Anisotropy of the hole-Mn interaction - Charge tunable Mn-doped QDs
3. Carriers and Mn spin dynamics
![Page 23: L.Besombes Y.Leger H. Boukari D.Ferrand H.Mariette J. Fernandez- Rossier CEA-CNRS team « Nanophysique et Semi-conducteurs » Institut Néel, CNRS Grenoble,](https://reader038.fdocuments.us/reader038/viewer/2022110323/56649d5d5503460f94a3cb16/html5/thumbnails/23.jpg)
Increase of the excitation density
Increase of the number of carriers in the QD.
Formation of the biexciton(binding energy 11meV)
Similar fine structure for the exciton and the biexciton
.
.
.
ehX
X2
eh
Biexciton in a Mn-doped QD
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Optical control of the magnetization:
- One exciton splits the Mn spin levels- With two excitons, the exchange interaction vanishes…
X2 (J=0)
X, J=±1
G.S.
σ +
σ -
Phys Rev B. 71, 161307(R) (2005)
Carrier controlled Mn spin splitting
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Charge tunable sungle Mn-doped QDs allow us to probe independantly the interactions between electron and Mn or hole and Mn
eh
eh
Phys Rev Lett. 97, 107401 (2006)
Gated charged Mn-doped quantum dots
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Ie-Mn = 40 μeV
Ih-Mn(X+) = 95 μeVIh-Mn(X) = 150 μeVIh-Mn(X-) = 170 μeV
♦ The hole confinement is influenced by the Coulomb attraction
X+, Mn X, Mn X-, Mn
Mn
h
e
Increasing the hole-Mn overlap by injecting electrons in the QD
X+, Mn hardly resolved
eh
eh
Variation of hole-Mn exchange interaction
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J=3
J=2
Final state:1 e + 1 Mn
•Isotropic e-Mn interaction•Anisotropic h-Mn interaction
Initial state:1 h + 1 Mn
eh
)S.j(I zzMnh
eh
2
5
2
5
2
5
2
5
Negatively charged exciton in a Mn doped QD
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J=3
J=2
2
5
♦ Optical transitions between:
hzeeMnz jSi
eMnzSf
Proportional to the overlap:
,SJ,J zz
Eigenstates of He-Mn
Jz=-1
Optical recombination of the charged exciton
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2
56
6
13,3
2
56
6
13,3
J=3
2
35
2
51
6
12,3
2
14
2
32
6
11,3
2
51
2
35
6
12,3
2
32
2
14
6
11,3
2
13
2
13
6
10,3
J=2
2
5
2
5
Energy
Prob
abil
ity
1
Optical recombination of the charged exciton
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J=3
J=2
2
5
2
5
2
31
2
55
6
12,2
2
12
2
34
6
11,2
2
55
2
31
6
12,2
2
34
2
12
6
112,
2
13
2
13
6
10,2
Energy
Prob
abil
ity
1
2
5
2
5
Optical recombination of the charged exciton
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J=3
J=2
2
5
2
5
Energy
Prob
abil
ity
1
e-Mn: isotropich-Mn: anisotropic
2
5
2
5
Optical recombination of the charged exciton
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J=3
J=2
Final state:1 e + 1 Mn
Initial state:1 h + 1 Mn
eh
))..(.( SjSjSjIlhzzMnh
(+3/2,-1/2)(-3/2,+1/2)
Phys Rev Lett. 97, 107401 (2006)
Charged exciton in a single QD: Influence of VBM
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J=3
J=2
Final state:1 e + 1 Mn
Initial state:1 h + 1 Mn
eh
))..(.( SjSjSjIlhzzMnh
(+3/2,-1/2)(-3/2,+1/2)
Charged exciton in a single QD: Influence of VBM
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♦ X-, Mn ♦ X+, Mn
e, Mn
h, Mn
h, Mn
e, Mn
♦ Reversed initial and final states
J=3J=2
Negatively / Positively charged Mn-doped QDs
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Heisenberg
ST
Q=-1 Q=0 Q=+1
Free
hh
Ising
Mz
Mn+1h= Nano-Magnet
En
ergy
Gated controlled magnetic anisotropy
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1. Probing the spin state of a single Magnetic atom - II-VI magnetic self assembled QDs - Carriers-Mn exchange interaction - Importance of QD structural parameters on the spin detection (Shape anisotropy, valence band mixing)
2. Carrier controlled Mn spin splitting
- Anisotropy of the hole-Mn interaction - Charge tunable Mn-doped QDs
3. Carriers and Mn spin dynamics
![Page 37: L.Besombes Y.Leger H. Boukari D.Ferrand H.Mariette J. Fernandez- Rossier CEA-CNRS team « Nanophysique et Semi-conducteurs » Institut Néel, CNRS Grenoble,](https://reader038.fdocuments.us/reader038/viewer/2022110323/56649d5d5503460f94a3cb16/html5/thumbnails/37.jpg)
Spin dynamics vs photon statistics
1 photon (σ, E) 1 Mn spin state
1 Mn atom Sz
If Sz(t=0) = -5/2
t0
1
~1/6
-5/2
?
P (Sz = -5/2)
-
-5/2
+5/2
…
+
+5/2
-5/2
…
Photon statistics ?
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Correlation measurement on single QDs
Use of a SIL to increase the signal
Select a QD witha large splittingto spectrally isolate a Mn spin state
PL
int
(arb
. uni
ts)
20402039203820372036 Energy (meV)
Single emitter statistics :
Antibunching: The QDs cannot emit two photons with a given energy at the same time
Whole PL autocorrelation
![Page 39: L.Besombes Y.Leger H. Boukari D.Ferrand H.Mariette J. Fernandez- Rossier CEA-CNRS team « Nanophysique et Semi-conducteurs » Institut Néel, CNRS Grenoble,](https://reader038.fdocuments.us/reader038/viewer/2022110323/56649d5d5503460f94a3cb16/html5/thumbnails/39.jpg)
Single Mn spin dynamicsP
L in
t (a
rb. u
nit
s)
20402039203820372036 Energy (meV)
Auto Correlation on one linein one polarization
One Mn spin projection
2zJ
1zJ
X X+Mn2+
E
τX-Mn
Photon bunching at short delay
8 ns
t
+, -5/2)
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PL
int
(arb
. un
its)
20402039203820372036 Energy (meV)
Auto Correlation on one linein one polarization
σ +
One Mn spin projection
2zJ
1zJ
X X+Mn2+
E
τX-Mn
Single Mn spin dynamics
Mixing between Mn spin relaxation time and X-Mn spin relaxation time
2 x P0
P0
3 x P0
Power dependence
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Single Mn spin dynamics
-
-5/2
+5/2
…
+
+5/2
-5/2
…
Direct evidence ofthe spin transfer
PL
int
(arb
. un
its)
20402039203820372036 Energy (meV)
Polarization Cross-Correlation
σ +
One Mn spin projection
σ -
Influence of magnetic field?...To be continued…
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Optical probing of a single carrier/single magnetic atom interaction.
- The exchange coupling is controlled by the carrier / Mn overlap.
- BUT, real self assembled QDs: - Shape anisotropy- Valence band mixing
…. Store information on a single spin?
Hole-Mn complex is highly anisotropic but non-negligeable effects of heavy-light hole mixing
Charged single Mn-doped QDs: Change the magnetic properties of the Mn with a single carrier.
Summary
Photon statistics reveals a complex spin dynamics.