Laser control of diluted magnetic semiconductors

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Spintronics and Magnetic Semiconductors
Joaquín Fernández-Rossier, Department of Applied
Physics, University of Alicante (SPAIN)

• Spintronics
• Magnetic Semiconductors
• Ferromagnetism in GaAsMn

Alicante, June 18 2003
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Spintronics
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Semiconductors
New exciting physics Quantum Hall
Effects, Conductance Quantization
Dimensional Reduction, Llt?B
Size reduction
Mesoscopic Behavior, Lltls

• Semiconductors
• Low carrier density (p, n)
• Heterostructures
• Electrical Control of p,n
• Volatile information

Single electron transistor
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Metallic Ferromagnets
Size reduction
New Physics GMR Lltlsr

• Ferromagnetic metals
• Collective Coordinate
• Permanent information
• High carrier density
• Heterostructures
• Magnetic Control of current

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There is plenty of room at the bottom R. P.
Feynman
There is plenty of room at the bottom R. P.
Feynman
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Alternative Approach Spintronics

• BUT
• Spin injection problem
• Spin scattering problem

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Spintronics (from the table of contents of
Semiconductor Spintronics and Quantum
Computation

• Device concepts
• Interface Physics (spin injection)
• Spin dynamics, spin decoherence
• Optical Manipulation
• Materials

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Magnetic Semiconductors (materials for
spintronics)
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History of magnetic semiconductors
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Ferromagnetism vs Paramagnetism
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V
VI
IV
III
B
C
N
O
Al
Si
P
S
II
Ga
Ge
As
Se
III-V Ga-As In-As Ga-Sb
In
Sn
Sb
Te
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Chemistry of II-VIMn and III-VMn
Electronic configuration of Mn 4s2 3d5
4p0 Electronic configuration of Ga (III) 4s2
3d10 4p1 Electronic configuration of Cd (II)
4s2 3d10 4p0

• Mn in III-V gives magnetic moment and holes
• Mn in II-VI gives magnetic moment

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• Spin Injection
• Heterostructures III-V (III,Mn)-V

• BUT
• Working at low temperature
• Small effects
• Curie Temperature lt 150 Kelvin

• Magnetic control of transport

• Electric control of Magnetism

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Magnetic Semiconductors Summary

• 2 types (ferro and para)
• Compatible with semiconductor technology
• Issue Increase Tc

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Microscopic mechanism of ferromagnetism
in (III,Mn)-V
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The mechanism. Experimental evidence

• II-VIMn PARAMAGNETIC
• II-VIMnelectrons, PARAMAGNETIC
• II-VIMn holes FERROMAGNETIC
• III-VMn FERROMAGNETIC

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Material Ga(1-x) AsMnx

• Ferromagnetic below 160 kelvin
• Homogeneous alloy for xlt0.10
• Transport p-doped semiconductor (pltcMn)

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Giant Zeeman Splitting in (II,Mn)-VI
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4 Exchange Interactions

• Coulomb Exchange ferromagnetic. (Reduction of
  Coulomb repulsion )
• Kinetic Exchange Antiferromagnetic

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The model Hamiltonian
Exchange
Non Magnetic Scattering
GaAs Hamiltonian
Sum over Impurities
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Carrier mediated ferromagnetism
Functional of carrier density matrix
Entropic Penalty
Paramagnetic gain
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Model Hamiltonian chemistry
s
EG
d
p
d
p
Holes in Valence Band
No fluctuationin d levels
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Ab initio chemistry
s
Holes in d levels.
d
Half metal?
p
d
p
Hund Exchange
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What about this chemistry?
Holes both in d levels and valence band.
s
d
Both Hund and Kinetic exchange
p
d
p
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Microscopic Mechanism Summary and questions

• Model Hamiltonian no d-charge fluctuations,
  holes in valence band, kinetic exchange. Weak
  coupling
• Double Exchange d charge fluctuations. Hund
  exchange. Strong coupling.
• Who is right? (from ab-initio)
• Interpolation from DE to KE

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JFR , in collaboration with
C. Piermarocchi Michigan State
P.C. Chen UC Berkeley
L. J. Sham UCSD
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Conclusions

• Spintronics make it happen ideology
• Magnetic Semiconductors bricks to build
  spintronics
• FM Mechanism maybe an open problem.