fundamental concepts of spintronics - uniba.sksophia.dtp.fmph.uniba.sk/~tatry/texty/fabian1.pdf ·...
TRANSCRIPT
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Fundamental concepts of spintronics
Jaroslav
Fabian
Institute for Theoretical PhysicsUniversity of Regensburg
Stara
Lesna, 24. 8. 2008 SFB 689
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:outline:
•
what is spintronics? •
spin injection
•
spin-orbit coupling in solids (next lecture)•
spin devices
•
conclusions: challenges
I. Zutic, J. Fabian, and S. Das Sarma, Spintronics: Fundamentals and applications, Rev. Mod. Phys. 76, 323 (2004)
J. Fabian, A. Matos-Abiague, C. Ertler, P. Stano, and I. Zutic,Semiconductor spintronics, Acta
Phys. Slov, 57, 566 (2007)
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what
is
spintronics?
narrow (device): electronics
with spin
broad: umbrella for electron spin
phenomena in solids
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spintronics drive
technology fundamental discoveries
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The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2007 jointly to
Albert Fert Unité
Mixte
de Physique CNRS/THALES, Université
Paris-Sud, Orsay, France
Peter Grünberg Forschungszentrum
Jülich, Germany,
"for the discovery of Giant Magnetoresistance".
The Nobel Prize in Physics 2007
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Giant MagnetoResistance P. Grunberg et al. (1988), A. Fert et al. (1988)
multilayers
30 -
40% at RT
small resistance large resistance
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GMR hard
disk
read
heads
From: IBM web site
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SPINTRONICS GOALSspin
control
of electrical
properties
(I-V characteristics)
electrical
control
of spin(magnetization)
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SPINTRONICS’
3 REQUIREMENTS
•
EFFICIENT SPIN INJECTION
•
SLOW SPIN RELAXATION @ SPIN CONTROL
•
RELIABLE SPIN DETECTION
Silsbee-Johnson spin-charge coupling
F N
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:(electrical) spin injection:
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Silsbee: emf
appears in the proximity of a ferromagnetic metal and spin-
polarized nonmagnetic metal (inverse of spin injection)
R. Silsbee, Bull. Mag. Reson. 2, 284 (1980)M. Johnson and R. H. Silsbee, Phys. Rev. Lett. 55, 1790 (1985).
spin injection spin detection
Johnson-Silsbee spin injection experiment
δMμ0μ0
E E
N (E) N (E) N (E) N (E)
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visualizing spin injection
S. A. Crooker et al., JAP, 101,081716 (2007)
S. A. Crooker at al., Science 309, 2191 (2005)
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spin injection into silicon
I. Appelbaum
et al, Nature 447, 295 (2007)I. Zutic
and J. Fabian, Nature (NW) 447, 269 (2007)
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spin injection into graphene
N. Tombros, C. Jozsa, M. Popinciuc, H. T. Jonkman, and B. J. van WeesElectronic spin transport and spin precession in single graphene layers at room temperature, Nature 448, 571 (2007)
N. Tombros, S. Tanabe, A. Veligura, C. Jozsa, M. Popinciuc, H. T. Jonkman, and B. J. van WeesAnisotropic spin relaxation in graphene, arXiv:0802.2892
single-layer on a SiO2
substrate, room temperature
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Zincblende
band structure (GaAs) optical
orientation
transitions
σ+σ+
mj
Eg
Δ
CB
SO
E
LH
HH
0 k
(a)
3/2P
1/2P
1/2S (b)
HH,LH
σ− −σ
1/2−1/2
−1/2 1/2
−3/2 3/2
−1/2 1/2
SO
CB
3 1 1 3
22Γ7
Γ8
6Γ
so
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
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:spin relaxation:
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t=0, spin imbalance t=T1
, spin balance
B Fe
impurity
phonon spin-orbit coupling
:key concepts: spin relaxation and dephasing
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:key concepts: spin relaxation and dephasing
Bloch eqs
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Time-resolved Faraday rotation
Source: web site of Awschalom’s
group
ZnCdSe
QW
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mechanisms of spin relaxation
J. Fabian, A. Matos-Abiague, C. Ertler, P. Stano, and I. Zutic,Semiconductor spintronics, Acta
Physica
Slovaca, 57, 565 (2007)
Elliott-Yafet mechanismelemental metals and semiconductors
Dyakonov-Perel mechanismSemiconductors without center of inversion symmetry
Bir-Aronov-Pikus mechanismHeavily p-doped semiconductors
Hyperfine interactionElectrons bound on impurity sites or confinedIn quantum dots
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spin
relaxation
in bulk
n-GaAs
τττττ
τ
relaxationtim
e(ns)
R. I. Dzhioev
et al., Phys. Rev. B 66, 245204 (2002)
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spin
relaxation
in bulk
n-Si
0 50 100 150 200 250 300Temperature [K]
0
20
40
60
80
100sp
in r
elax
atio
n tim
e T
1 [ns
] 7.4 1014
3.7 1015
4.5 1015
7.8 1015
2.7 1016
8.0 1016
D. Lepine, Phys. Rev. B 6, 436 (1972)
J. Fabian, A. Matos-Abiague, C. Ertler, P. Stano, and I. Zutic, Acta
Physica
Slovaca, 57, 565 (2007)
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:spin devices: (spin detection)
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:semiconductor
spintronics devices:
•
spin resonant diodes•
spin
field-effect
transistors•
magnetic
semiconductor
tunnel
junction
devices•
magnetic
bipolar junction
diodes and transistors•
spin
optoelectronic devices•
spin
galvanics devices•
spin Hall polarizeds•
spin-polarized
semiconductor
lasers•
spin pumping batteries•
spin-torque devices•
spin
quantum
computers•
...
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J. Fabian, A. Matos-Abiague, C. Ertler, and P. Stano,Semiconductor spintronics, Acta
Phys. Slov, 57, 566 (2007)
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International Technology Roadmap for Semiconductors:
Emerging Research Logic Devices
risk
RSFQ1-D
structuresresonanttunneling SET molecular QCA
spin transistor
2004
2005, 2006
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International Technology Roadmap for Semiconductors:
Emerging Research Logic Devices
risk
RSFQ1-D
structuresresonanttunneling SET molecular QCA
spin transistor
2004
2007
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detour: material case study: GaMnAs
• 5-15 % Mn• p-doped (Mn
replaces Ga) • degenerate: p = 1020
- 1021/cm3
• Tc
= 170 K• ferromagnetism and carrier density coupled• kλ
about 3 (localization?)• impurity or valence band?• quantum coherence effects observed
GaMnAs, from Jungwirth et al, Rev. Mod. Phys. 78, 809 (2006)
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Where does GaMnAs
fit? No good answer yet
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b)
BeZnSe
ZnMnSeZnSe
ZnSe
BeZnSeBeZnSe
ZnMnSeZnSe
ZnSe
BeZnSe
magnetic
Resonant
Tunnel
Diodes A. Slobodskyy
et al, Phys. Rev. Lett. 90, 246601 (2003)
C. Ertler
and J. Fabian, Appl. Phys. Lett. 89, 193507 (2006)
C. Ertler
and J. Fabian, Phys. Rev. B 75 195323 (2007)
• efficient spin filtering• spin detection• fast switching times• coherence issues• RT operation?
6T
3T
0T
8% Mn
T=1.3K
a)
ZnSeZnMnSe
ZnSe
B
1.3
K
Voltage (0-0.2 V)
Cur
rent
(0-1
50 μ
A)
0 0.05 0.1 0.15 0.2 0.250
0.5
1
1.5
2
2.5
3x 10
5
Voltage (V)
Cur
rent
Den
sity
(A
/cm
2 )
0 10 20 300
50
100
z (nm)
Ene
rgy
(meV
)
Δ E = 0
Δ E = 5 meV
Δ E = 10 meV
Δ E = 15 meV
Δ E = 20 meV
Δ E = 25 meV
Δ E = 40 meV
T = 4.2 K
ΔV2out
ΔV3out
ΔV1out
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:selfsustained magneto-electric oscillations in MRTDs:
C. Ertler
and J. Fabian, Phys. Rev. Lett. 101, 077202 (2008)
0 10 20 300
5
10
x 1015
Voltage (mV)j (
a.u.
)
jmax
jmin
I
II
(a)
0 10 20 300
5
10
15
20
Voltage (mV)
Δ (m
eV)
Δmax
Δmin
(b)
II
I
50 100 150 2000
5
10
x 1015
Time (t*)
j (a.
u.)
jtot
j↑j↓
(c)
50 100 150 2002
4
6
8
10
12
14x 1011
Time (t*)
n (1
/cm
2 )
ntot
n↑
n↓
(d)
Intrinsic bistability
leads to temporal oscillations in the current, magnetizaion, and particle density
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:nanospintronics:spin-based quantum information processing
D. Loss and D. P. DiVincenzo, PRA 57, 120 (1998)
• single and few spins manipulation and detection• spin relaxation and decoherence• entanglement control (EDAP: Fabian and Hohenester, PRB 72, 201304 (R) 2005)
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closing: challenges in spintronics
•
room-temperature ferromagnetic semiconductors, n and p type, identification of mechanisms for ferromagnetic long-range order
•
magnetic heterostructures: ferromagnetic quantum wells and quantum dots
•
spin-polarized transport through magnetic interfaces and inhomogeneities, accurate determination of spin polarization of ferromagnets
•
development of silicon (Si, Si:Ge) spintronics: spin injection, spin relaxation, magnetism (?), quantum dots
•
demonstration of semiconductor spin transistors--power gain and magnetologic:spin FETs, bipolar spin transistors
•
niche devices for GaMnAs
or other dilute magnetic semiconductors, specific functionalities
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closing: challenges in spintronics
•
control of ferromagnetism by gating or current injection, spin-transfer torque
•
spin dynamics and spin pumping phenomena in spin transport
•
control of spin-orbit coupling by gate and doping, interface properties
•
single channel devices
•
Spin transport in carbon nanotubes, graphene
•
spin quantum information processing:single and few spin manipulation, relaxation and decoherence, spin entanglement control