Post on 12-Sep-2021
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WHAT IS SPINTRONICS?
What is spintronics?electronics with a spin
GMR (giant magnetoresistance) effect
GMR hard disk read heads
From: IBM web site
GOAL
• spin control of electrical properties(I-V characteristics)
• electrical control of spin(magnetization)
Applications:•magnetic read heads•nonvolatile RAM•quantum computing (?)
New directionssemiconductor spintronics
• spin field-effect devices• magnetic semiconductor tunnel junction devices• magnetic bipolar junction devices• spin optoelectronics• spin galvanics• mesoscopic spintronics• spin-polarized semiconductor lasers• spin torque• spin quantum computing• ...
Datta-Das Spin FETS. Datta and B. Das, Appl. Phys. Lett. 56, 665 (1990)
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
SPINTRONICS’ 3 REQUIREMENTS
• EFFICIENT SPIN INJECTION
• SLOW SPIN RELAXATION
• RELIABLE SPIN DETECTION
MRFM single spin detection(magnetic resonance force microscopy)
IBM web site D. Rugar et al., Nature 430, 329 (2004)
OPTICAL SPIN ORIENTATION
Zincblende band structureoptical orientation transitions
σ+σ+
mj
Eg
∆
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)
Zincblende k=0 Bloch statessymmetries
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
Dresselhaus (BIA) and Bychkov-Rashba field patterns
SIA
[111]BIA
[001]BIA
BIA [110]
110110
001
100010
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
SPIN RELAXATION and SPIN DYNAMICS
Spin relaxation in metals:Elliott-Yafet theory
R. J. Elliott, Phys. Rev. B 96, 266 (1954)Y. Yafet, in Solid State Physics, Vol. 14, p.2 (1963)
=
__
Phonon-induced spin relaxation in aluminum
Spin relaxation in bulk n-GaAs
τττττ
τ
relaxationtim
e(ns)
R. I. Dzhioev et al., Phys. Rev. B 66, 245204 (2002)
Spin relaxation in GaAs/AlGaAs QWvs confinement energy (DP--quadratic)
E1e (m eV)0 20 40 60 80 100 120 140
SpinRelaxationRate(ps-1)
0.00
0.02
0.04
0.06
0.08
0.10
A. R. Malinowski et al. Phys. Rev. B 62, 13034 (2000).
SPIN INJECTION
F/N spin injection
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
spin injection into semiconductors• Theoretically predicted by
A. G. Aronov and G. E. Pikus, Fiz. Tekh. Poluprovodn. 10, 1177 (1976) [Sov. Phys. Semicond. 10, 698-700 (1976)]
• Experimentally first realized byM. Johnson and R. H. Silsbee, Phys. Rev. Lett. 55, 1790 (1985)
• Experimental realization in semiconductors:
Fiederling et al. Nature 402, 787 (1999).Ohno et al. Nature 402, 790 (1999).
Electroluminescence in a ZnMnSeLED
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8
EL
Po
lariza
tio
n(%
)
Magnetic Field (T)
T = 4.5 K
1.52 1.53 1.54 1.55 1.56 1.57
EL
Inte
nsity
(arb
.u
nits)
Photon Energy (eV)
0
0.5
2
4 T
T = 4.5 K�+
�-
(a) (b)
B. T. Jonker et al., App. Phys. Lett. 79, 3089 (2001)
F/I/F tunnel junction
F2F1 F2F1
(a)
E E
I I
(b)
E E
N (E) N (E) N (E) N (E) N (E) N (E) N (E) N (E)
∆ex
subbandminority−spin majority−spin
subband
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
SPINTRONIC DEVICES
Datta-Das Spin FETS. Datta and B. Das, Appl. Phys. Lett. 56, 665 (1990)
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
Magnetic tunnel transistor
M
Fermi level
CoFeGaAs
IC
VBCVEB
eVEB IECoFe
Emitter
Base
Collector
Fermi level
Al O2 3
�
M1
2 34
A
S. Van Dijken, PRL 90, 197203 (2003)
Loss-DiVincenzospin quantum computer
D. Loss and D. P. DiVincenzo, PRA 57, 120 (1998).
From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)
magnetic bipolar diode
Make use of the existing device structures
CONVENTIONAL DIODE 101
p-n junction formation
before:
during:
p-n junction diode
p-n junction diodeequilibrium
p region: holes n region: electrons
equilibrium currents
thermal generationthermal activation
in equilibrium Jf=Jr=Jg
p-n junction diodenonequilibrium
p region n region
Forward bias: J=Jg exp(V/kBT) Reverse bias: J=Jg
Magnetic bipolar diode(giant) magnetoresistance
Magnetic Bipolar Diode spin in equilibrium:
no spin-charge coupling
Spin-charge coupling:large current
Spin-charge coupling:small current
GMR in MBT numericallyspin-voltaic effect
V=0.8 VGaAs
I. Zutic, J. Fabian, and S. Das Sarma, Phys. Rev. Lett. 88, 066603 (2002).
spin injection?
ONLY AT LARGE BIASES!
I. Zutic, J. Fabian,S. Das Sarma, Phys. Rev. B. 64, 121201 (2001).
spin-polarized bipolar transport
Bipolar spin-polarized transportnumerical modeling
• electron and hole drift in external + intrinsic E-field• electron and hole diffusion• magnetic drift (Stern-Gerlach-like)• spin diffusion• electron-hole recombination• spin relaxation• Poisson’s equation (selfconsistency)
+ boundary conditions (ohmic contacts, spin injection)
magnetic bipolar transistor
CONVENTIONAL TRANSISTOR 101
Magnetic Bipolar Transistor
J. Fabian, I. Zutic and S. Das Sarma, Appl. Phys. Lett. 84, 85 (2004);J. Fabian and I. Zutic, Phys. Rev. B 69, 115314 (2004).
MBTintrinsic spin extraction/injection
efficiency exp(qVbe/kBT)
104
106
108
1010
1012
1014
1016
1018
n, s
(cm
-3)
electron density nspin density s
0 1 2 3 4 5x (µ)
00.20.40.60.8
α
0 1 2-10
-3
0
magnetic baseP0=0.67Vbe=0.5 VVbc=0 V
J. Fabian and I. Zutic, Phys. Rev. B 69, 115314 (2004)
GIANT MAGNETOAMPLIFICATION EFFECT
J. Fabian and I. Zutic, Phys. Rev. B 69, 115314 (2004)