l.besombes y.leger h. boukari d.ferrand h.mariette j. fernandez-rossier
DESCRIPTION
Optical control of an individual spin. L.Besombes Y.Leger H. Boukari D.Ferrand H.Mariette J. Fernandez-Rossier. CEA-CNRS team « Nanophysique et Semi-conducteurs » Institut Néel, CNRS Grenoble, FRANCE. Department of applied physics, University of Alicante, SPAIN. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
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
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.
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)
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
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 In
tens
ity (a
rb. u
nits
)
Energy (meV)
meV50
eV50
100 m
Micro-spectroscopy.Micro-spectroscopy.
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
Electrical control of the charge.
Transfer of holes from the surface states: p type doping of the QDs.
V
p-ZnTeCdTe
Gated charged quantum dots
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
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
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
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
Magnetic field dependent PL intensity distribution.
NMn=0 NMn=1
Mn-doped individual QDs under magnetic field
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
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
S.I Mne
j.I he
zzBhzzBe BjμgBσμg
2B
zzMnh .Sj I
zzBMn BSμg
-1 0 1 2Energy (meV)
Th.Exp. Effective spin Hamiltonian:
Carriers-Mn exchange coupling
- X-Mn Overlap- QD shape- Strain distribution
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
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
Inhomogeneous relaxation of strain in a strained induced QD (Bir & Pikus Hamiltonian):
0.. SjSjI Mnh
|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
123,
23
1310
32
21,
23
k
E
Valence band mixing in strained induced QDs
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
))..(.( SjSjSjI lhzzMnh
2zJ
1zJ
X X+Mn2+
~~
Influence of valence band mixing
Allows simultaneous hole-Mn spin flip
Effective h-Mn interaction term in the Heavy hole Subspace
eh
eh
lh : Heavy-light hole mixing efficiency
))..(.( SjSjSjI lhzzMnh 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
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)
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
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
X2eh
Biexciton in a Mn-doped QD
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
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
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
J=3
J=2Final 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
25
25
25
25
Negatively charged exciton in a Mn doped QD
J=3J=2
25
♦ 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
256
613,3
256
613,3
J=3
235
251
612,3
214
232
611,3
251
235
612,3
232
214
611,3
213
213
610,3
J=2
25
25
Energy
Prob
abili
ty
1
Optical recombination of the charged exciton
J=3J=2
25
25
231
255
612,2
212
234
611,2
255
231
612,2
23
421
26
112,
213
213
610,2
Energy
Prob
abili
ty
1
25
25
Optical recombination of the charged exciton
J=3J=2
25
25
Energy
Prob
abili
ty
1
e-Mn: isotropich-Mn: anisotropic
25
25
Optical recombination of the charged exciton
J=3
J=2Final state:1 e + 1 Mn
Initial state:1 h + 1 Mn
eh
))..(.( SjSjSjI lhzzMnh
(+3/2,-1/2)(-3/2,+1/2)
Phys Rev Lett. 97, 107401 (2006)
Charged exciton in a single QD: Influence of VBM
J=3
J=2Final state:1 e + 1 Mn
Initial state:1 h + 1 Mn
eh
))..(.( SjSjSjI lhzzMnh
(+3/2,-1/2)(-3/2,+1/2)
Charged exciton in a single QD: Influence of VBM
♦ 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
Heisenberg
ST
Q=-1 Q=0 Q=+1
Free
hh
Ising
Mz
Mn+1h= Nano-Magnet
Ene
rgy
Gated controlled magnetic anisotropy
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
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 ?
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 in
t (ar
b. u
nits
)
20402039203820372036 Energy (meV)
Single emitter statistics :
Antibunching: The QDs cannot emit two photons with a given energy at the same time
Whole PL autocorrelation
Single Mn spin dynamicsPL
int (
arb.
uni
ts)
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)
PL in
t (ar
b. u
nits
)
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
Single Mn spin dynamics
-
-5/2
+5/2
…
+
+5/2
-5/2
…
Direct evidence ofthe spin transfer
PL in
t (ar
b. u
nits
)
20402039203820372036 Energy (meV)
Polarization Cross-Correlation
σ +
One Mn spin projection
σ -
Influence of magnetic field?...To be continued…
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.