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Spin-Hall field effect transistors

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SemiSpinNet. Spin-Hall field effect transistors. University of Nottingham Tomas Jungwirth, Richard Campion , et al. Hitachi Cambridge Joerg W ü nderlich , Andrew Irvine , et al. Institute of Physics ASCR Kamil Olejnik , Tomas Jungwirth , Vít Novák, et al. - PowerPoint PPT Presentation
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SemiSpinN et Research fueled by: ASRC Workshop on Magnetic Materials and Nanostructures Tokai, Japan January 10 th , 2012 Vivek Amin, JAIRO SINOVA Texas A&M University Institute of Physics ASCR Hitachi Cambridge Joerg Wünderlich, Andrew Irvine, et al Institute of Physics ASCR Kamil Olejnik, Tomas Jungwirth, Vít Novák, et al University of Nottingham Tomas Jungwirth, Richard Campion, et al. Spin-Hall field effect transistors
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Page 1: Spin-Hall field effect transistors

SemiSpinNet

Research fueled by:

ASRC Workshop on Magnetic Materials and Nanostructures

Tokai, JapanJanuary 10th, 2012

Vivek Amin, JAIRO SINOVATexas A&M University

Institute of Physics ASCR

Hitachi CambridgeJoerg Wünderlich, Andrew Irvine, et al

Institute of Physics ASCRKamil Olejnik, Tomas

Jungwirth, Vít Novák, et al

University of Nottingham Tomas Jungwirth,

Richard Campion, et al.

Spin-Hall field effect transistors Spin-Hall field effect transistors

Page 2: Spin-Hall field effect transistors

2Nanoelectronics, spintronics, and materials control by spin-orbit coupling

I. Optical injection spin-Hall FET•Spin based FET: old and new paradigm in charge-spin transport•Theory expectations and modeling•Experimental results•Spin-current AND-gate

II. Spin Hall and non-local spin valve detection of electrically injected and manipulated spins:

•Spin amplifier and modulator•non-local spin accumulation measurements•Device and key issues•Modeling

III. Summary

spin-Hall field effect transistors spin-Hall field effect transistors

Page 3: Spin-Hall field effect transistors

3

Spin-orbit coupling interaction

(one of the few echoes of relativistic physics in the solid state)

This gives an effective interaction with the electron’s magnetic moment

Consequences•Effective quantization axis of the spin depends on the momentum of the electron. Band structure (group velocities, scattering rates, etc.) mixed strongly in multi-band systems

•If treated as scattering the electron gets asymmetrically scattered to the left or to the right depending on its “spin”

Classical explanation (in reality it is quantum mechanics + relativity )

• “Impurity” potential V(r) Producesan electric field

∇V

BBeffeff

pss

In the rest frame of an electronthe electric field generates and effective magnetic field

• Motion of an electron

Page 4: Spin-Hall field effect transistors

4

Problem: Rashba SO coupling in the Datta-Das SFET is used for manipulation of spin (precession) BUT it dephases the spin too quickly (DP mechanism).

From DD-FET to new paradigm using SO coupling

1) Can we use SO coupling to manipulate spin AND increase spin-coherence?

• Can we detect the spin in a non-destructive way electrically?

3) Can this effect be exploited to create a spin-FET logic device?

Use the persistent spin-Helix state or quasi-1D-spin channels and control of SO coupling strength (Bernevig et al 06, Weber et al 07, Wünderlich et al 09, Zarbo et al 10)

Use AHE to measure injected current polarization electrically (Wünderlich, et al Nature Physics. 09, PRL 04)

Spin-Hall AND-gate device (Wünderlich, Jungwirth, et al Science 2010)

DD-FET

Page 5: Spin-Hall field effect transistors

5

Spin-dynamics in 2D electron gas with Rashba and Dresselhauss SO coupling

a 2DEG is well described by the effective Hamiltonian:

Something interesting occurs when

[110]

[110]_

α = 0, β < 0 [110]

[110]_

ky [010]

kx [100]

α > 0, β = 0

1) Can we use SO coupling to manipulate spin AND increase spin-coherence?

Page 6: Spin-Hall field effect transistors

6

Local spin-polarization → calculation of AHE signal

Weak SO coupling regime → extrinsic skew-scattering term is dominant

Lower bound estimate

Spin-injection Hall effect: theoretical expectations

1) Can we use SO coupling to manipulate spin AND increase spin-coherence?

• Can we detect the spin in a non-destructive way electrically?

Use the persistent spin-Helix state or 1D-spin channelsand control of SO coupling strength

Use AHE to measure injected current polarization electrically

Page 7: Spin-Hall field effect transistors

7

Spin-injection Hall device measurements

trans. signal

σσooσσ++σσ-- σσoo

VL

SIHE ↔ Anomalous Hall

Wunderlich, Irvine, Sinova, Jungwirth, et al, Nature Physics 09

Page 8: Spin-Hall field effect transistors

8

T = 250K

Further experimental tests of the observed SIHE

Page 9: Spin-Hall field effect transistors

9

VH2

I

VbVH1

x

VH2

VbVH1

x

(a)

(b)

Spin injection Hall effect

Wunderlich, et al, Science 2010

SiHE

inverse SHE

Page 10: Spin-Hall field effect transistors

Spin-FET with two gates → logic AND function

Wunderlich et al., Science.‘10

SHE transistor AND gate

Page 11: Spin-Hall field effect transistors

11Nanoelectronics, spintronics, and materials control by spin-orbit coupling

I. Optical injection spin-helix and spin-Hall FET•Spin based FET: old and new paradigm in charge-spin transport•Theory expectations and modeling•Experimental results•Spin-current AND-gate

II. Spin Hall and non-local spin valve detection of electrically injected and manipulated spins:

•Spin amplifier and modulator•non-local spin accumulation measurements•Device and key issues•Modeling

III. Summary

spin-Hall field effect transistors spin-Hall field effect transistors

Page 12: Spin-Hall field effect transistors

+

ID

+

Electrical injection, manipulation, and detection of spins in semiconductors

Electrical injection spin-amplifier (modulator) in Fe/GaAs(3D)

FM FM

FM FM

injection from a FM detection of spin current by iSHE

detection of spin polarization by FM

electrical manipulation of the spin profile by a drift current

Huang et al 07

Page 13: Spin-Hall field effect transistors

Experimental device set-up

IB ID

Fe FeAu Au

VSH

VNL

n-GaAs

Note: ID reminiscent of base current in the bipolar transistor amplifier IB ↔ emitter current detected spin polarization (current) ↔ collector current

Page 14: Spin-Hall field effect transistors

14

Electrical non-local spin valve detection by FM and by iSHE

Electrical injection of a diffusive spin current from FM into a non-magnetic metal

Valenzuela, S. O. & Tinkham, M, Nature‘06

iSHE NL spin detection

Page 15: Spin-Hall field effect transistors

Valenzuela, S. O. & Tinkham, M, Nature‘06

xy

zBz

Electrical non-local spin valve detection by FM and by iSHE

Electrical injection of a diffusive spin current from FM into a non-magnetic metal

iSHENL spin detection

Page 16: Spin-Hall field effect transistors

16

high-resitive semiconducor

low-resistive FM metal

Lou et al. Nature Phys.’07, Ciorga et al. PRB 09, Awo-Affouda et al. APL 09, Salis et al. PRB 09

Fe/n-GaAs Schottky tunnel contacts

very high-resitivespin-dependent tunnel contact↓

Electrical non-local spin valve detection by FM and by iSHE

Electrical injection of a diffusive spin current from FM into a non-magnetic semiconductors

Page 17: Spin-Hall field effect transistors

17

high-resitive semiconducor

low-resistive FM metal

Lou et al. Nature Phys.’07, Ciorga et al. PRB 09, Awo-Affouda et al. APL 09, Salis et al. PRB 09

Fe/n-GaAs Schottky tunnel contacts

... and by iSHE ?

very high-resitivespin-dependent tunnel contact↓

Electrical non-local spin valve detection by FM and by iSHE

Electrical injection of a diffusive spin current from FM into a non-magnetic semiconductors

Page 18: Spin-Hall field effect transistors

n-GaAs

FeAl

xy

z

xy

zBz

Key is to experimentally remove the strong ordinary Hall effect in SCs

Page 19: Spin-Hall field effect transistors

n-GaAs

Al

BX

x

y

z

x

y

z

Fe

Key is to experimentally remove the strong ordinary Hall effect in SCs

Hanle + iSHE

Page 20: Spin-Hall field effect transistors

Baniso ≈ 200 mT >> BHanle ≈ 50 mT

BX

x

y

z

x

Epitaxial 2 nm Fe on n-GaAs grown in one MBE → large [110]/[1-10] in-plane anisotropy

Page 21: Spin-Hall field effect transistors

Plus we know when each Fe electrode switches for a given φB

Bx

y

z

Page 22: Spin-Hall field effect transistors

(ordinary Hall)

BX

x

y

z

x

iSHE

Hanle iSHE

Page 23: Spin-Hall field effect transistors

Easy-axis switching NL spin-valve

Hanle iSHEHard-axis Hanle NL spin-valve

Page 24: Spin-Hall field effect transistors

Nuclear (Overhauser) field:

xy

z

Bz

BX

x

y

z

Bz,aniso ≈ 2 T

Bx,aniso ≈ 200 mT

Hanle curves affected by nuclear fields

Page 25: Spin-Hall field effect transistors

Hanle curves affected by nuclear fields

Page 26: Spin-Hall field effect transistors

iSHE reverses sign upon reversing spin-current

Page 27: Spin-Hall field effect transistors

Electrical spin modulator

Bx=0

Page 28: Spin-Hall field effect transistors

Drift-diffusion equations

1. sy continuous at x=0

2. independent of vd(x)

Bx=0

Page 29: Spin-Hall field effect transistors

Drift velocities

Diffusion constant

Spin lifetime

Bx=0

Overall magnitude ( source term )

Page 30: Spin-Hall field effect transistors

TheoryExperiment

Page 31: Spin-Hall field effect transistors

Spin current

Hall sensitivity function for a finite-size cross

iSHE voltage

(~ skew scattering Hall angle in GaAs)

SHE analysis from calibrated spin-current

Page 32: Spin-Hall field effect transistors

TheoryExperiment

Page 33: Spin-Hall field effect transistors

Experiment Theory

skew scattering Hall angle in GaAs:

Theory - experiment comparison

Summary of theory

•DD-equation with non-constant vd analysis•Spin-lifetime from out of plane Hanle•Fit of DD to NL yields polarization at injection FM electrode•Use this injected spin-current estimate to calculate predicted spin Hall angle (because of geometry one needs to calculate the sensitivity function for the Hall cross bar).

Page 34: Spin-Hall field effect transistors

34

Summary of spin-injection Hall FET

Basic studies of spin-charge dynamics and Hall effect in non-magnetic systems with SO coupling Spin-photovoltaic cell: solid state polarimeter on a semiconductor chip requiring no magnetic elements, external magnetic field, or bias

SIHE can be tuned electrically by external gate (e.g. Fe/Ga(Mn)As structures)

Spin amplifier-modulator based on drift current iSHE and NL in semiconductor device

Strongest theory-experiment comparison to date in SC

optical-spin-injection Hall FET

all electrical Hall FET


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