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)