From ferromagnetic to non-magnetic semiconductor spintronics: Spin-injection Hall effect

Tomas Jungwirth

University of Nottingham Bryan Gallagher, Richard Campion, Kevin

Edmonds, Andrew Rushforth, et al.

Hitachi Cambridge, Univ. Cambridge Jorg Wunderlich, Andrew Irvine, Byonguk Park, et al.

Institute of Physics ASCRJairo Sinova, Karel Výborný, Jan Zemen, Jan Mašek, Alexander Shick, František Máca,

Jorg Wunderlich, Vít Novák, Kamil Olejník, et al.

Texas A&M University

Jairo Sinova, Liviu Zarbo, et al.

Inductive read elements Magnetoresistive read elements

AMR and GMR (TMR) sensors: dawn of spintronics

1980’s-1990’s

~ 1% MR effect~ 1% MR effect

Ferromagnetism & spin-orbit coupling anisotropic magnetoresistance

Lord Kelvin 1857

magnetization

current

Ferromagnetism only giant (tunnel) magnetoresistance

~ 100% MR effect~ 100% MR effect

Fert, Grunberg et al. 1988

Coulomb blockade AMR: likely the most sensitive spintronic transistors to date

Wunderlich et al. PRL ’06Schlapps et al. PRB `09

Renewed interest in SO induced MRs in ferromagnetic semiconductors

~ 1000% MR effect & gate controlled~ 1000% MR effect & gate controlled

Ohno Science ’98

p- or n-type FET depending on magnetization non-volatile programmable logic, etc.

V

I

_ FL

Ordinary Hall effect:response in normal metals to external magnetic field via Lorentz force

Anomalous Hal effect:response to internal spin polarization in ferromagnets via spin-orbit coupling

Hall 1879

I

_ FSO__

V

Hall 1881

M

SO induced MRs: AMR & anomalous Hall effect

B

Tc in (Ga,Mn)As upto ~190 K but AHE survives and dominates HE far above Tc

Ruzmetov et al. PRB ’04

OHE AHE

j=3/2

HH

HH & LH Fermi surfaces

(Ga,Mn)As: simple band structure of the host SC

Spherical HH Kohn-Luttinger 3D model Rashba and Dresselhaus 2D models

QuantitativeAHE theoryJungwirth et al. PRL ’02

Intense theory research of AHE in model 2D R&D systems

Nagaosa et al RMP ‘’09 in press (arXiv:0904.4154)

EveSmc

H SO

2

1

I || E

_ FSO

FSO

_ __

Spin Hall effectspin-dependent deflection transverse edge spin polarization

Taming spins in non-magnetic materials: spin-Hall effectTaming spins in non-magnetic materials: spin-Hall effect

Wunderlich et al. arXives ’04 (PRL ’05)Kato et al. Science ’04

V

I

_ FL

Ordinary Hall effect:response in normal metals to external magnetic field via classical Lorentz force

Anomalous Hal effect:response to internal spin polarization in ferromagnets via quantum-relativistic spin-orbit coupling

Hall 1879

I

_ FSO__

V

Hall 1881

MB

Polarized EL from a planar LED

Theory and experiment: ~10% polarization over ~10nm wide edge region

Wunderlich et al. Nature Phys.‘09

More taming of spins by spin-orbit couplingMore taming of spins by spin-orbit coupling

Spin-injection from a ferromagnet

Ferromag

net

Wunderlich et al. Nature Phys.‘09

More taming of spins by spin-orbit couplingMore taming of spins by spin-orbit coupling

Spin-injection by incident circularly polarized light

+

Wunderlich et al. Nature Phys.‘09

More taming of spins by spin-orbit couplingMore taming of spins by spin-orbit coupling

Spin-injection Hall effect

– – –

+ + +

+

Spin-dependent deflection due to spin-orbit coupling

Wunderlich et al. Nature Phys.‘09

More taming of spins by spin-orbit couplingMore taming of spins by spin-orbit coupling

Spin-injection Hall effect

– – – – – – – – – – – –

+ + + + + + + + + + + +

+

Spin-dependent deflection due to spin-orbit coupling transverse (Hall) electrical voltage in steady state

Bernevig et al., PRL`06, Wunderlich et al. Nature Phys.‘09

More taming of spins by spin-orbit couplingMore taming of spins by spin-orbit coupling

Spin-injection Hall effect

– – + + – –

+ + – – + +

+

Built-in electric fields in SC structure another spin-orbit coupling effect which can lead to spin precession

Hall voltages measure local spin orientation

Bernevig et al., PRL`06, Wunderlich et al. Nature Phys.‘09

More taming of spins by spin-orbit couplingMore taming of spins by spin-orbit coupling

Spin-injection Hall effect

– – + + – –

+ + – – + +

+

Built-in electric fields in SC structure can be modified by external gate voltage

Hall signals changed by gate transverse-voltage spintronic transistor

Bernevig et al., PRL`06, Wunderlich et al. Nature Phys.‘09

More taming of spins by spin-orbit couplingMore taming of spins by spin-orbit coupling

Spin-injection Hall effect

VG

– – + + – – + + – –

+ + – – + + – – + +

+

Built-in electric fields in SC structure can be modified by external gate voltage

Hall signals changed by gate transverse-voltage spintronic transistor

2DHG

2DEG

e

h

e eee

e

hhh

h h

VH

Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell

Optical spin-generation area near the p-n junction

Simulated band-profile

p-n junction bulit-in potential (depletion length ) ~ 100 nm self-focusing of the generation area of counter-propagating e- and h+

Hall probes further than 1m from the p-n junction safely outside the spin-generation area and/or masked Hall probes

2DHG2DEG

e

h

eee

e

e

h hh

hh

Vb

VH2

VL

2DHG2DEG

ee

hh

eeeeee

ee

ee

hh hhhh

hhhh

Vb

VH2

VL

Experimental observation of the SIHE

SIHE linear in degree of polarization and spatially varying

> 0, = 0 = 0, < 0

yyxxyxxy kkkkmkH

2

222DEG

Spin dynamics in Rashba&Dresselhaus SO-couped 2DEG

k-dependent SO field strong precession & spin-decoherence due to scattering

[1-10]

[110]

No decoherence for || = || & channel SO field

/4

/

]101[

]101[]101[

tk

mtkL

Bernevig et al PRL’06

))(V(2 dis

*22

rkkkkkmkH yyxxyxxy

2DEG

]exp[)( ]011[]011[ xqxpZ

2~~4~~~

arctan

)~~~(||,)exp(||

21

22

41

22

21

21

4142

22

21

LLLLL

LLLqiqq

22/1 ||2~ mL

Diffusive spin dynamics & Hall effect due to skew scattering

)(2)( ]011[*

]011[ xpnnex zi

H

precession-length (~1m) >> mean-free-path (~10 nm)

~10nm

Basic studies of spin-charge dynamics and Hall effect in non-magnetic systems with SO coupling Spin-photovoltaic cell: polarimeter on a SC chip requiring no magnetic elements, external magnetic field, or bias; unconventional laser displacement sensor with the resolution defined by the spin-precession length built in the SC

SIHE can be tuned electrically by external gate and combined with electrical spin- injection from a ferromagnet (e.g. Fe/Ga(Mn)As structures)

Conclusions

SIHE: high-T SO only spintronics in non-magnetic systems

Ohno et al. Nature’99, others

Crooker et al. JAP’07, others Magneto-optical imagingnon-destructive

lacks nano-scale resolution and only an optical lab tool

MR Ferromagnet electrical

requires semiconductor/magnet hybrid design & B-field to orient the FM spin-LED all-semiconductor

requires further conversion of emitted light to electrical signal

SIHE vs other spin-detection tools in semiconductors

Spin-injection Hall effect

non-destructive

electrical

100-10nm resolution with current lithography

in situ directly along the SC channel & all-SC requiring no magnetic elements in the structure or B-field