coherently induced ferromagnetism in diluted magnetic semiconductors southampton, oces9-sces2...
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Coherently induced ferromagnetism inDiluted Magnetic Semiconductors
Southampton, OCES9-SCES2 September 7st 2005
Joaquín Fernández-RossierDept. Física Aplicada, Univ de Alicante,Spain
[email protected]. Slides in www.ua.es/personal/jfrossier/
Collaboration with:C. Piermarocchi (Michigan State), P. Chen (Taiwan), A. H. MacDonald (University of Texas),L. J. Sham, (UC San Diego)
G. Chiappe, E. Louis, E. Anda (Alicante)
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Coherently induced ferromagnetism inDiluted Magnetic Semiconductors
Southampton, OCES9-SCES2 September 7st 2005
Joaquín Fernández-RossierDept. Física Aplicada, Univ de Alicante,Spain
[email protected]. Slides in www.ua.es/personal/jfrossier/
(Zn,Mn)S
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Coherently induced ferromagnetism inDiluted Magnetic Semiconductors
Southampton, OCES9-SCES2 September 7st 2005
Joaquín Fernández-RossierDept. Física Aplicada, Univ de Alicante,Spain
[email protected]. Slides in www.ua.es/personal/jfrossier/
Magnetic OrderInduced by subgapLaser radiation
(Zn,Mn)S
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Magnetic ImpuritiesLocalized ElectronsNuclei
Elaser>E
G
REAL population of electrons and holesCarrier Mediated Exchange Interactions
,k ,k',' k
'11 SS '22 SS
Optically Induced Exchange Interactions
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Magnetic ImpuritiesLocalized ElectronsNuclei
VIRTUAL electrons and holesCarrier Mediated Exchange Interactions
,k ,k',' k
'11 SS '22 SS
22 EPn
COHERENTLY Induced Exchange Interactions
Elaser<E
G
C. Piermarocchi, P. Chen, L.J. Sham and D. G. Steel, PRL89 , 167402 (2002)
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SYSTEM 1BULK diluted magnetic semiconductors (DMS) PARAMAGNETIC to FERROMAGNETIC transition
SYSTEM 23D Optical Cavity + Quantum Dot + 2 Mn atoms Full Quantum mechanical analysis of Optical RKKY
JFR, cond-mat 0508235 (2005)G. Chiappe, JFR, et al., cond-mat 0407639 (2004)
JFR, C. Piermarocchi, P. Chen, A. H. MacDonald, L. J. Sham,Phys. Rev. Lett 93, 127201, (2004)
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OUTLINE•DMS•ORKKY: macro and micro•Coherently Induced Ferromagnetism•CAVITY-Spin-doped Dot
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B C
Al Si
N O
P S
Ga Ge
In Sn
As Se
Sb
II
Zn
Cd
Hg
IV VIII VI
TeII-VIZn-SeZn-S Cd-Te
EF
II-VI Semiconductors
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B C
Al Si
N O
P S
Ga Ge
In Sn
As Se
Sb Te
Zn
Cd
Hg
Mn
EF
(II,Mn)-VI PARAMAGNETIC Semiconductors
(II,Mn)-VI(Zn,Mn)-Se(Zn,Mn)-S (Cd,Mn)-Te
Zn: Ar: 3d10 4s2
Mn: Ar: 3d5 4s2
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B C
Al Si
N O
P S
Ga Ge
In Sn
As Se
Sb Te
Zn
Cd
Hg
Mn
EF
(II,Mn)-VI PARAMAGNETIC Semiconductors
(II,Mn)-VI(Zn,Mn)-Se(Zn,Mn)-S (Cd,Mn)-Te
Mn: neutral impurity, SPIN S=5/2 (3d5)
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EXCHANGE INTERACTIONS
iihih
iieie
iiii
AF
rSMJ
rSMJ
MMiiJH
)(
)(
)',( '',
Superexchange (AF)
Conduction Band
Valence Band
EF
1
2
he JJ41
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OPTICAL EXCHANGE INTERACTION.MACROSCOPIC THEORY
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Macroscopic Explanation of optical ferromagnetism
EEU L'
Reactive optical energy, due to matter-laser interaction:
•U depends on M
•Ferromagnetism
(M>0) minimizes U (M)•But entropy favors M=0
Competition between reactive optical energy and entropy
Electric Field of the Laser
Real part of retarded Optical Response function
•U depends on bands
•Bands Depend on M
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<M>=0
L
jecMn<M>
jhcMn<M>
B
100 meV
PH
OT
ON
EN
ER
GY
(eV
)
(II,Mn)-VI
Bands DEPEND on Mn magnetization
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Confined Levels depend on Mn state
EXPERIMENTS:L. Besombes et al., PRL 93, 207403, (2004)Y. Léger et al. PRL. 95, 047403 (2005)
THEORY: J. Fernández-Rossier, cond-mat/0508235
CdTe nanocrystal +1Mn
SINGLE SPIN DETECTION !!!
2S+1=6
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CdTe+ 1Mn Quantum Dot:Carrier interacts with 1 Mn
J. Fernández-Rossier, cond-mat/0508235
MSJH
I
Ik MkSkJ
MJcMnkk
Bulk (II,Mn)VI: carrier interacts with many Mn
.. BECAUSE OF EXCHANGE
LjecMn<M>
jhcMn<M>
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OPTICAL EXCHANGE INTERACTION.microSCOPIC THEORY
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Microscopic Theory: HAMILTONIAN
Mean Field, VC aprox, HF-Pairing
JFR, C. Piermarocchi, P. Chen, A. H. MacDonald, L. J. Sham,Phys. Rev. Lett 93, 127201, (2004)
KEY PARAMETERS
2
23
0
na
Ed
E
cv
LG
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k
kkH
2
1
kU
kL
kE
EH
0
0
2
1
EU(k)
EL(k)
Rotating FrameRWA
00
01
2
2
vuv
uvu Coherent
Occupation
Microscopic Theory: Density Matrix
L
01
T
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RESULTS for Zn0.988 Mn0.012 S
Hamiltonian + Density Matrix + approximations yield U(M) (reactive energy),S(M) (entropy)
MneMnh cJcJ ,,,
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0 1 2M
-1.45
-1.44
-1.43
-1.42
-2
(b)
-0.4
-0.2
0-K
BT
S T=115 mKT=105 mK
(a)
-2 -1 0 1 2M
-1.2
-1
U
0 0.5 1T /TC
0
1
2
M
=26 meV, TC=780 mK
=41 meV, TC=114 mK
=71 meV, TC=22 mK
Results for (Zn0.988,Mn0.012) S
G
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1.50
1.00
0.50
Transition Temperature for (Zn0.988,Mn0.012) S
Linear response fails there
3
2
cT
1.02
23
na
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Transition Temperature for (Zn0.988,Mn0.012) S
Also from ORKKY+ Mean Field
ji
jiORKKY SSjiJH,
),(
ORKKY:C. Piermarocchi, P. Chen, L.J. Sham and D. G. SteelPRL89 , 167402 (2002)
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Isothermal transitions for (Zn,Mn) S
T=0.5 K
Switching ferromagnetis
m on and off
!!!
JFR, C. Piermarocchi, P. Chen, A. H. MacDonald, L. J. Sham,Phys. Rev. Lett 93, 127201, (2004)
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Experimental Issues
• Materials:– Moderate x (avoid superexchange)– Large exciton binding energy (osc.
Stre)
• Detection: Easy (polarized PL)• Smal detuning vs unwanted heating• Transition Time vs Laser Pulse
duration
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Ferromagnetic Transition Time
0 1 2M
Gib
bs
Free E
nerg
y
0 1 2M
0 1 2M
Laser off Laser OnTL<T1
Laser OnTL>T1
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Cavity-Dot ORKKY. Motivation
• Effect of exciton dimensionality (JFR, L. Brey, PRL 2004)
• Confine Photons (increase Rabi)(G. Chiappe, JFR et al., condmat 2004)
Optical RKKY in the Cavity-QD system:•Photons are treated quantum mechanically•Mn-exciton interaction is treated exactly•Photon-exciton interaction is treated exactly
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Cavity Dot System. State of the Art
J. P. Reithmaier et al., Nature 432, 197 (2004)
III-V
g=0.1 meV g=16 meV
M. Obert, APL 84,1435 (2004)
Magnetic tuning in excitonic Bragg structures of (Cd,Mn)Te/(CdTe)J. Sadowski, H. Mariett, A. Wasiela, R. André, Y. Merle d’Aubigné, T. DietlPhys. Rev. B56, R1664 (1997)
II-VI
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Cavity Dot System
1P,0X
0X,0P
1X,0P
Photon
LOWER ENERGY EXCITED STATE:Half and Half
Exciton
0
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Cavity Dot System
Exciton
1P,0X
0X,0P
1X,0P Photon
1P+0X
1X,0P
LOWER ENERGY EXCITED STATEMOSTLY Photon
0
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Cavity Dot System
Exciton 1P,0X
0X,0P
1X,0P
Photon
LOWER ENERGY EXCITED STATEMOSTLY Exciton
0
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Single Spin conditional Cavity Tuning
1P,0X
0X,0P
1X(+1),0P(-)Mn(-5/2)
Photon
LOWER ENERGY EXCITED STATEMOSTLY Exciton
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Single Spin conditional Cavity Tuning
1P,0X
0X,0P
Photon
LOWER ENERGY EXCITED STATEMOSTLY Exciton
1X(+1),0P(-)Mn(+5/2)
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Cavity + QD exciton + 2 Mn
G. Chiappe, JFR, et al., condmat 2004
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Cavity –QD exciton – 2 Mn
2,1'''' )()(
21
),,(
IIeh
ehhehe
dc
MccIJddIJ
bcddcb
ddEccEbbHF
G. Chiappe, JFR, et al., condmat 2004
Single Cavity mode, Single exciton
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CAVITY DOT spin correlationT= 1 Kelvin
121 MM
REGION I
REGION III
REGION II
0
0
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1.50
1.00
0.50
BULK Tc (ORKKY)
CAVITY DOT spin correlationT= 1 Kelvin
121 MM
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OutlookIncoherent exciton coupling (magnetic polarons)
Experiments and theory
Virtual excitons (ORKKY)
Theory
Polariton exciton (QORKKY)
TheoryExperiment: Planar Cavities with Mn
Condensed exciton coupling (BEC-RKKY)
Theory (GIANT POLARON)PRB 1998, Kavokin
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CONCLUSIONS
• New mechanism for ferromagnetism: coherently photoinduced
• Cavity + Spin Doped Dot: non-trivial spin-photon-exciton correlations
Email: [email protected] available in www.ua.es/personal/jfrossier/