Dynamical Effects in Semiconductor Spintronics

8/8/2019 Dynamical Effects in Semiconductor Spintronics

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Fourth Basic Circuit Element

V i

q

Voltage, V Current, A

Charge, C Flux, Wb

Resistor:

Capacitor:

Inductor:

Memristor:


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Memristive systems

itiwMV ),,(=

),,( tiwfdt

dw

=

Current-controlled

Memristive system

w = a set of n-state

variables

VtVwGi ),,(=

),,( tVwfdtdw =

Voltage-controlled

Memristive system

itqMV ))((=Ideal memristor Chua, 71


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Properties

1. Passivity criterion: .0),,( tiwM

2. No energy discharge property: . 0)()()( = titVtp

3. Frequency behavior: - as a non-linear resistor at low frequencies;

- as a linear resistor at high frequencies.

4. Doubled-valued Lissajous figure property.

V

i

Pinched Hysteresis Loop

Memristor Fingerprint


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Realizations and Applications

Non-volatile memory Programmable logic

Signal Processing

Neural networks

Thermistors

Ion channelsResistive switching systems:

Binary oxides: TiO2, CuO, NiO, CoO, Fe2O3 Strukov et al.,

Nature 2008

Perovskite oxides: SrTiO3, Pr1-x CaxMnO3

Sulfides: Cu2S, Ag2S

Organics: CuTCNQ, MIM (with pentacene, TPD, AIDCN, )

Semiconductors: GaAs, ZnSe-Ge

Spintronics devices

App

lic

ati

ons

Rea

liza

tions


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Semiconductor spintronics systems

YVP and M. Di Ventra,Phys. Rev. B 78,113309 (2008)

Requirements to observe memristive effects in semiconductor spintronics:

Transport properties should depend on the level of electron-spin polarization in a

semiconductor

Spin polarization in semiconductor should be influenced by an external control

parameter (applied current or voltage).Spin injection Spin extraction

An example:

semiconductor/half-metal junctions


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+V

Semiconductor

with non-degenerate electron gas

Half-metal

Spin-down cloud

YVP and M. Di Ventra, Phys. Rev. B 75, 193301 (2007).

j

Spin blockade


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Critical current: drift-diffusion equations

SemiconductorHalf-metal j

( )( ) ( ) ( )( )

+=

nn

ej

t

ne

sf2div

( ) ( ) ( )+=neDEj x

( )nNe

Ex =0

div

relaxation

diffusion

drift


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SemiconductorHalf-metal j

From condition n(0)=0 we find:

Critical current:

Critical electric field:

For GaAs, jc=10-7

A/m2

,

Boundary conditions fordrift-diffusion model:

j(0)=0 j()=j/2

j(0)=j j()=j/2

0 1 2 3 4 5 6 7 80.00

0.25

0.50

0.75

1.00

n/N

0

x

nn

Critical current

V


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Possible application:

Current stabilization device

Current-voltage characteristics

SC

A

FMcontact

V=Vcont +VSC

j~n(0) Vcont

0 10 20 30 40 500.0

0.2

0.4

0.6

0.8

1.0

j/jc

V/(sL jc )

c

0/(

sL)=0.1

c

0/(

sL)=0.5

c0/(

sL)=1

c

0/(

sL)=5

c

0/(

sL)=10


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Spin memristive systems

Memristive systemw = a set of n-state

variables

ItIwMV ),,(=

),,( tIwf

dt

dw=

In

NLV cs )

)0(2( 00

+=

( )( ) ( ) ( )( )

+=

nn

ej

t

ne

sf2div


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Spin memristive systems

A

FM contact SC

j


very low frequencies: nonlinear resistor

very high frequencies: linear resistor


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0 2 4 6 8 100

3

6

9

0.0

0.5

1.0

1.5

V(V)

j/jc

Time (ns)

Transient response

Current spikes!

j~n(0) Vcont

Usual conductors:

Ohms law I=V/R


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Memristive spin Hall effect



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Outline

Memory effects in semiconductor

spintronics

Spin generation in closed geometries


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Spin Hall and stirring effects

Y. K. Kato et al., Science 306, 1910 (2004) M. Switkes et al., Science 283, 1905 (1999)


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Main idea

V1(t)

V2

(t)V3

(t)

V4(t)

I

YVP, N. A. Sinitsyn, A. Kogan, A. Saxena, D. L. Smith, Appl. Phys. Lett. 95, 022114


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Results: current and potential

-1.5

-1.0

-0.5

(V)

y

(m)

0

1

2

01

2x

(m)

GaAs,R=1m, n=1015 cm-3 ,E0=5kV/cm

Averaged current density Potential distribution


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Results: spin polarization

0 1 2 3 4 52

3

4

5

6

7

8

9

0.2 0.4 0.6 0.8 1.00.01

0.1

1

10

pz

(10-4)

p

z(10

-4)

T(ns)

n (1016

cm-3)


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Different number of electrodes

= 3/2= 2/=

-6.000E-4

-3.500E-4

-1.000E-4

1.500E-4

4.000E-4

6.500E-4

9.000E-4

0.001150

0.001400

0.001600


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Screening effects

0 1 2 3 4 52

3

4

5

6

7

8

9

0.2 0.4 0.6 0.8 1.00.01

0.1

1

10

pz

(10

-4)

p

z(10-4)

T(ns)

n (1016cm-3)

-8.000E-5

-6.750E-5

-5.500E-5

-4.250E-5

-3.000E-5

-1.750E-5

-5.000E-6

7.500E-6

2.000E-5

-3.500E-4

-2.000E-4

-5.000E-5

1.000E-4

2.500E-4

4.000E-4

5.500E-4

7.000E-4

8.000E-4

n=1015

cm-3

n=1016

cm-3


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Conclusions

Short time memory effects are intrinsic in many

semiconductor spintronics devices

Transient response of semiconductor spintronics

devices may limit their operational frequency

All-electrical spin polarization generation scheme is

suggested based on a combination of Spin Hall

effect and stirring effect Such a scheme can be used, e.g., to control

magnetization of nano-magnets

Dynamical Effects in Semiconductor Spintronics

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