WHAT IS SPINTRONICS?

What is meant by spin?

I. Ensemble spin (magnetization)

II. Spin dynamics(ensemble phaseevolution) B

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 (?)

Tunnel MagnetoResistance

TMR about 50-100%

small resistance large resistance

F I F

Julliere 1975; Moodera et al. 1995

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• ...

SPINTRONICS’ 3 REQUIREMENTS

• EFFICIENT SPIN INJECTION

• SLOW SPIN RELAXATION

• RELIABLE SPIN DETECTION

Silsbee-Johnson spin-charge coupling

F N

MRFM single spin detection(magnetic resonance force microscopy)

IBM web site D. Rugar et al., Nature 430, 329 (2004)

SPIN RELAXATION and SPIN DYNAMICS

:key concepts: spin relaxation and dephasing

Bloch eqs

t=0, spin imbalance t=T1, spin balance

B Fe

Spin relaxation for pedestrians

impurity

phononSpin-orbit coupling

Elliott-Yafet

Mechanisms of spin relaxation

metalssmall gap zincblende semiconductors (InSb)semiconductors with inversion symmetry (Si)

Bir-Aronov-Pikus

Dyakonov-Perel

n III-V (GaAs)n II-VI (ZnSe)

From: J. Fabian and S. Das Sarma, J. Vac. Sc. Technol. B 17, 1708 (1999)

p III-V (GaAs, GaSb)

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)

Time-resolved Faraday rotation

Source: web site of Awschalom’s group

ZnCdSe QW

Spin relaxation in bulk n-GaAs

τττττ

τ

relaxationtim

e(ns)

R. I. Dzhioev et al., Phys. Rev. B 66, 245204 (2002)

SPIN INJECTION

:key concepts: spin injection and detection

Material (input) parameter (0 in para for weak injection, ~40% in ferromagnets)

δM

NF

x0

(a)

(b)

j

M

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)

Aronov: spin can be injected into nonmagnetic conductor by driving electric current from a ferromagnetic electrode

spin injection spin detection

spin diffusion

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).

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8E

LP

ola

rization

(%)

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�+

�-

B. T. Jonker et al., Appl. Phys. Lett. 79, 3098 (2001)

Electroluminescence in a spin LEDZnMnSe aligner

spin injection into semiconductors

Fiederling et al. Nature 402, 787 (1999); Ohno et al. Nature 402, 790 (1999).

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)

Δex

subbandminority−spin majority−spin

subband

From: I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys. 76, 323 (2004)

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)

SPINTRONIC DEVICES

spin-orbit coupling in zincblende systemswhat happens when inversion symmetry is broken?

Yu. A. Bychkov and E. I. Rashba, J. Phys. C 17, 6039 (1984); JETP Lett. 39, 78 (1984)

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)

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 junction transistorS. Van Dijken, X. Jiang, and S. Parkin, Phys. Rev. Lett. 90, 197203 (2003)

M

Fermi level

CoFeGaAs

IC

VBCVEB

eVEB IECoFe

Emitter

Base

Collector

Fermi level

Al O2 3

�

M1

2 34

A

• hybrid structures• large magnetocurrent• useful for interface characterization• spin filter • large base current small or no gain

b)

BeZnSe

ZnMnSeZnSe

ZnSe

BeZnSeBeZnSe

ZnMnSeZnSe

ZnSe

BeZnSe

Spin resonant diodesA. Slobodskyy et al, Phys. Rev. Lett. 90, 246601 (2003)

• efficient spin filtering• spin detection

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)

International Technology Roadmap for Semiconductors 2004:

Emerging Research Devices

risk

RSFQ1-D

structuresresonanttunneling SET molecular QCA

spin transistor

Logic devices

: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, cond-mat/0412229)

Table 1 Curie temperatures for several new ferromagnetic semiconductor systems. All compounds except for MnGeP2 are doped, carrier-mediated ferromagnets. [from S. Wolf et al., IBM. J. Res. & Dev. 50, 101 (2006)]

Material Curie temp. Year

GaMn0.05As 110 K250 K

(1998)(2004)

GaMn0.05Sb 25 K80 K

(1999)(2003)

MnxGe 25–116 K (2002)

CoxTiO2 600 K (2001)GaMnxN 400 K (2001)

MnGeP2 340 K (2001)

CoxSnO2−δ 600 K (2003)

La0.5Sr0.5Ti0.985Co0.015O3 450 K (2003)

CrxZnTe >300 K (2003)

Zn0.978Mn0.022O ~300 K (2003)

In1.7Sn0.2Mn0.1O3−δ ~300 K (2004)

AlxGa1−xCryN 800–900 K (2002–2004)