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SPIN-HALL EFFECT SPIN-HALL EFFECT a new adventure in condensed matter physicsa new adventure in condensed matter physics
San Houston State University, January 22th 2008
JAIRO SINOVA
Research fueled by:
NERC
Branislav NikolicU. of DelawareAllan MacDonald
U of Texas
Tomas JungwirthInst. of Phys. ASCR
U. of Nottingham
Joerg WunderlichCambridge-Hitachi
Laurens MolenkampWuerzburg
Kentaro NomuraU. Of Texas
Ewelina HankiewiczU. of MissouriTexas A&M U.
Mario BorundaTexas A&M U.
Nikolai SinitsynTexas A&M U.
U. of Texas
Other collaborators: Bernd Kästner, Satofumi Souma, Liviu Zarbo, Dimitri Culcer , Qian Niu, S-Q Shen, Brian
Gallagher, Tom Fox, Richard Campton, Winfried Teizer, Artem Abanov
Sergio RodriguezTexas A&M U.
Xin LiuTexas A&M U.
Alexey KovalevTexas A&M U.
OUTLINEOUTLINE From electronics to spintronics:From electronics to spintronics:
Electron multipersonality: using the charge and using the Electron multipersonality: using the charge and using the spinspin
Success stories of metal based spintronicsSuccess stories of metal based spintronics Why semiconductor spintronics may be betterWhy semiconductor spintronics may be better Spin-orbit coupling: the necessary evilSpin-orbit coupling: the necessary evil The usual example: Das-Datta transistorThe usual example: Das-Datta transistor
Spin-Hall effect: Spin-Hall effect: Normal and anomalous Hall effect and Spin Hall effect Normal and anomalous Hall effect and Spin Hall effect
Three contributions to the AHEThree contributions to the AHE Turbulent history of the AHETurbulent history of the AHE Recent focus on the intrinsic AHERecent focus on the intrinsic AHE Application to the SHEApplication to the SHE Short but turbulent history of the SHEShort but turbulent history of the SHE
SHE experimentsSHE experiments Resolution of some of the controversyResolution of some of the controversy Spin Hall spin accumulationSpin Hall spin accumulation Theory challengesTheory challenges Experimental challengesExperimental challenges
ELECTRONICSELECTRONICS
UP TO NOW: all electronics are mostly basedon the manipulation of the charge of the electron so perhaps we should say “charge electronics”
Mr. Electron Two parts to hispersonality !
CHARGE
SPIN
SPINTRONICS: manipulate spin SPINTRONICS: manipulate spin and charge simultaneouslyand charge simultaneously
What is What is spintronics?spintronics?
Using the chargeUsing the charge
substrate
semiconductor
insulatorS Dgate
Vg
thin free charge carrierchannel induced by
electric field from gate
- - - - - -
>0
High mobility 2DEG: IQHE, FQHE, MIT, etc.
ALL computers have thesetransistors in one form or another
HIGH tunablity of electronic transportproperties the key to FET success in processing technology
the field effect transistor:the field effect transistor: work horse of information work horse of information processingprocessing
Using the spinUsing the spin
ferromagnetism:ferromagnetism: work horse of information work horse of information storingstoring
1st generation spintronic devices based on ferromagnetic metals: GMR– already in every computer
GMR allowed read-out heads in hard drives to be MUCH smaller
Magnetic tunneling junction (MTJ) or “spin valve” Nonvolatile MRAM: “Microchips that never forget ”
Compatibility with Si and GaAs next phase: semiconductor spintronics, a marriage of convenience!!!
A brighter future with semiconductor spintronicsA brighter future with semiconductor spintronics
MORE KNOBS = MORE PHYSICS
Can do what metals doCan do what metals do- GMR, TMR in diluted magnetic semi-cond., spin transfer,
etc.
Easy integration with semiconductor devicesEasy integration with semiconductor devices- possible way around impedance mismatch for spin
injection.
More tunable systemsMore tunable systems
- transport propertiestransport properties: carrier concentration is tuned by gates and chemical doping
- ferromagnetic state affected by carrier concentration (DMS) - optical control of non-equilibrium populations
Possibility of new physical regimes/effectsPossibility of new physical regimes/effects- TAMR - tunable spin-orbit couplingspin-orbit coupling
Necessities in performing Necessities in performing spintronics in semiconductorsspintronics in semiconductors
Spin-generation: “spin battery”Spin-generation: “spin battery” - injection (conventional)- optical, via selection rules (excitation with circular polarized light)- via SO coupling (e.g., occupation-asymmetry in k-space, Spin Hall
effect)Spin-manipulation- external magnetic field- via SO coupling (e.g. Datta Das Spin-transistor)
Spin-detection: “spin meter”- Magnetoresistive measurement (conventional) - optical, via selection rules (Spin LED)- via SO coupling (e.g., anomalous Hall effect)
Spin-orbit coupling interactionSpin-orbit coupling interaction
(one of the few echoes of relativistic physics in the solid state)(one of the few echoes of relativistic physics in the solid state)
Ingredients: -“Impurity” potential V(r)
- Motion of an electron
)(1
rVe
E
Producesan electric field
In the rest frame of an electronthe electric field generates and effective magnetic field
Ecm
kBeff
This gives an effective interaction with the electron’s magnetic moment
LSdr
rdV
err
mc
k
mc
SeBeffH SO
)(1
CONSEQUENCES•If part of the full Hamiltonian quantization axis of the spin now
depends on the momentum of the electron !! •If treated as scattering the electron gets scattered to the left or to
the right depending on its spin!!
Using SO: Datta-Das spin FET
V
- vBeff
- vBeff
-v
Beff
V/2
Datta-Das spin FET: the Datta-Das spin FET: the moviemovie
Movie created by Mario Borunda
OUTLINEOUTLINE From electronics to spintronics:From electronics to spintronics:
Electron multipersonality: using the charge and using the Electron multipersonality: using the charge and using the spinspin
Success stories of metal based spintronicsSuccess stories of metal based spintronics Why semiconductor spintronics may be betterWhy semiconductor spintronics may be better Spin-orbit coupling: the necessary evilSpin-orbit coupling: the necessary evil The usual example: Das-Datta transistorThe usual example: Das-Datta transistor
Spin-Hall effect: Spin-Hall effect: Normal and anomalous Hall effect and Spin Hall effect Normal and anomalous Hall effect and Spin Hall effect
Three contributions to the AHEThree contributions to the AHE Turbulent history of the AHETurbulent history of the AHE Recent focus on the intrinsic AHERecent focus on the intrinsic AHE Application to the SHEApplication to the SHE Short but turbulent history of the SHEShort but turbulent history of the SHE
SHE experimentsSHE experiments Resolution of some of the controversyResolution of some of the controversy Spin Hall spin accumulationSpin Hall spin accumulation Theory challengesTheory challenges Experimental challengesExperimental challenges
SPIN HALL EFFECTSPIN HALL EFFECTA NEW TWIST ON AN OLD HATA NEW TWIST ON AN OLD HAT
References:N. A. Sinitsyn, J.E. Hill, Hongki Ming, Jairo Sinova, and A. H. MacDonald, Phys. Rev. Lett. 97, 106804 (2006)
Jairo Sinova, Shuichi Murakami, S.-Q. Shen, Mahn-Soo Choi, Solid State Comm. 138, 214 (2006).K. Nomura, J. Wunderlich, Jairo Sinova, B. Kaestner, A.H. MacDonald, T. Jungwirth, Phys. Rev. B 96, 076804 (2006).
B. Kaestner, J. Wunderlich, Jairo Sinova, T. Jungwirth, Appl. Phys. Lett. 88, 091106 (2006).K. Nomura, Jairo Sinova, N.A. Sinitsyn, and A. H. MacDonald, Phys. Rev. B. 72, 165316 (2005).
E. M. Hankiewicz, Tomas Jungwirth, Qian Niu, Shun-Qing Shen, and Jairo Sinova, Phys. Rev. B.72, 155305 (2005).N.A. Sinitsyn, Qian Niu, Jairo Sinova, K. Nomura, Phys. Rev. B 72, 045346 (2005).
Branislav K. Nikolic, Satofumi Souma, Liviu P. Zarbo, Jairo Sinova, Phys. Rev. Lett. 95, 046601 (2005). Joerg Wunderlich, Bernd Kaestner, Jairo Sinova, Tomas Jungwirth, Phys. Rev. Lett. 94, 047204 (2005).K. Nomura, Jairo Sinova, T. Jungwirth, Q. Niu, A. H. MacDonald, Phys. Rev. B 71, 041304(R) (2005).E. M. Hankiewicz, L.W. Molenkamp, T. Jungwirth, and Jairo Sinova, Phys. Rev. B 70, 241301 (2004)N. A. Sinitsyn, E. H. Hankiewicz, Winfried Teizer, Jairo Sinova, Phys. Rev. B 70, 081212 (R), (2004).
D. Culcer, Jairo Sinova, N. A. Sinitsyn, T. Jungwirth, A.H. MacDonald, Qian Niu, Phys. Rev. Lett 93, 046602 (2004). Jairo Sinova, Dimitrie Culcer, Q. Niu, N. A. Sinitsyn, T. Jungwirth, A.H. MacDonald, Phys. Rev. Lett. 92, 126603 (2004).
Anomalous Hall effect: where things Anomalous Hall effect: where things started, the unresolved problemstarted, the unresolved problem
MπRBR sH 40
Simple electrical measurement Simple electrical measurement of magnetizationof magnetization
Spin-orbit coupling “force” deflects like-spinlike-spin particles
I
_ FSO
FSO
_ __
majority
minority
VInMnAs
controversial theoretically: three contributions to the AHE (intrinsic deflection, skew scattering, side jump scattering)
Intrinsic Intrinsic deflectiondeflection
Electrons have an “anomalous” velocity perpendicular to the electric field related to their Berry’s phase curvature which is nonzero when they have spin-orbit coupling.
Movie created by Mario Borunda
Electrons deflect to the right or to the left as they are accelerated by an electric field ONLY because of the spin-orbit coupling in the periodic potential (electronics structure)
Skew Skew scatteringscattering
Movie created by Mario Borunda
Asymmetric scattering due to the spin-orbit coupling of the electron or the impurity. This is also known as Mott scattering used to polarize beams of particles in accelerators.
Side-jump Side-jump scatteringscattering
Movie created by Mario Borunda
Related to the intrinsic effect: analogy to refraction from an imbedded medium
Electrons deflect first to one side due to the field created by the impurity and deflect back when they leave the impurity since the field is opposite resulting in a side step.
(thanks to P. Bruno– CESAM talk)
A history of controversy
THE THREE CONTRIBUTIONS TO THE AHE: THE THREE CONTRIBUTIONS TO THE AHE: MICROSCOPIC KUBO APPROACHMICROSCOPIC KUBO APPROACH
Skew scattering
Side-jump scattering
Intrinsic AHE: accelerating between scatterings
SkewσH
Skew (skew)-1 2~σ0 S where
S = Q(k,p)/Q(p,k) – 1~
V0 Im[<k|q><q|p><p|k>]
Vertex Corrections σIntrinsic
Intrinsicσ0 /εF
n, q
n, q m, p
m, pn’, k
n, q
n’n, q
FOCUS ON INTRINSIC AHE: semiclassical and KuboFOCUS ON INTRINSIC AHE: semiclassical and Kubo
K. Ohgushi, et al PRB 62, R6065 (2000); T. Jungwirth et al PRL 88, 7208 (2002);T. Jungwirth et al. Appl. Phys. Lett. 83, 320 (2003); M. Onoda et al J. Phys. Soc. Jpn. 71, 19 (2002); Z. Fang, et al, Science 302, 92 (2003).
'
2
'
'
2
)(
'ˆˆ'Im]Re[
nnk knkn
yx
nkknxy EE
knvknknvknff
V
e
nk
nknxy kfV
e
)(]Re[ '
2
Semiclassical approach in the “clean limit”
Kubo:
n, q
n’n, q
STRATEGY: compute this contribution in strongly SO coupled ferromagnets and compare to experimental results, does it work?
Success of intrinsic AHE approach in Success of intrinsic AHE approach in comparing to experiment: comparing to experiment: phenomenological “proof”phenomenological “proof”• DMS systems (Jungwirth et al PRL 2002, APL 03)
• Fe (Yao et al PRL 04)• layered 2D ferromagnets such as SrRuO3 and
pyrochlore ferromagnets [Onoda and Nagaosa, J. Phys. Soc. Jap. 71, 19 (2001),Taguchi et al., Science 291, 2573 (2001), Fang et al Science 302, 92 (2003), Shindou and Nagaosa, Phys. Rev. Lett. 87, 116801 (2001)]
• colossal magnetoresistance of manganites, Ye et~al Phys. Rev. Lett. 83, 3737 (1999).
• CuCrSeBr compounts, Lee et al, Science 303, 1647 (2004)
Berry’s phase based AHE effect is quantitative-successful in many instances BUT still not a theory that treats systematically intrinsic and extrinsic contribution in an equal footing AND supposedly equivalent theories
give different results when disorder is incorporated.
Experiment AH 1000
(cm)-1
TheroyAH 750 (cm)-1
Spin Hall effectSpin Hall effect
Take now a PARAMAGNET instead of a FERROMAGNET: Spin-orbit coupling “force” deflects like-spinlike-spin particles
I
_ FSO
FSO
_ __
V=0
non-magnetic
Spin-current generation in non-magnetic systems Spin-current generation in non-magnetic systems without applying external magnetic fieldswithout applying external magnetic fields
Spin accumulation without charge accumulationSpin accumulation without charge accumulationexcludes simple electrical detectionexcludes simple electrical detection
Carriers with same charge but opposite spin are deflected by the spin-orbit coupling to opposite sides.
Spin Hall Effect(Dyaknov and Perel)
InterbandCoherent Response
(EF) 0
Occupation # Response
`Skew Scattering‘(e2/h) kF (EF )1
X `Skewness’
[Hirsch, S.F. Zhang] Intrinsic
`Berry Phase’(e2/h) kF
[Murakami et al,
Sinova et al]
Influence of Disorder`Side Jump’’
[Inoue et al, Misckenko et al, Chalaev et al…] Paramagnets
INTRINSIC SPIN-HALL EFFECT: INTRINSIC SPIN-HALL EFFECT: Murakami et al Science 2003 (cond-mat/0308167)
Sinova et al PRL 2004 (cont-mat/0307663)
as there is an intrinsic AHE (e.g. Diluted magnetic semiconductors), there should be an intrinsic spin-Hall
effect!!!
km
kkk
m
kH xyyxk
0
22
0
22
2)(
2
Inversion symmetry no R-SO
Broken inversion symmetry R-SO
Bychkov and Rashba (1984)
(differences: spin is a non-conserved quantity, define spin current as the gradient term of the continuity equation. Spin-Hall conductivity: linear response of this operator)
n, q
n’n, q
‘‘Universal’ spin-Hall conductivityUniversal’ spin-Hall conductivity
*22*
2
2
4
22*22
sH
for8
for8
DDD
D
DD
xy
nnn
ne
mnn
e
Color plot of spin-Hall conductivity:yellow=e/8π and red=0
n, q
n’n, q
SHE conductivity: all contributions– Kubo formalism perturbation theory
Skewσ0 S
Vertex Corrections σIntrinsic
Intrinsicσ0 /εF
n, q
n’n, q
= j = -e v
= jz = {v,sz}
Disorder effects: beyond the finite Disorder effects: beyond the finite lifetime approximation for Rashba lifetime approximation for Rashba
2DEG2DEGQuestion: Are there any other major effects beyond
the finite life time broadening? Does side jump contribute significantly?
Ladder partial sum vertex correction:
Inoue et al PRB 04Raimondi et al PRB 04Mishchenko et al PRL 04Loss et al, PRB 05
~
the vertex corrections are zero for 3D hole systems (Murakami 04) and 2DHG (Bernevig and Zhang 05)
n, q
n’n, q
+ +…=0
For the Rashba example the side jump contribution cancels the intrinsic contribution!!
k1 Rashba: g=constant α = 1 k3 Rashba: g=constant α = 3
Nomura et al. PRB 06
2DEG+Rahsba
2DHG+Rahsba
For these models one can do the exact calculations numerically: testing the perturbation theory
4.6
k^3 Rashba model k^1 Rashba model
Numerical results for SHE conductivities Numerical results for SHE conductivities in 2D electrons and in 2D holesin 2D electrons and in 2D holes
iEE
njnnjn
EE
EfEf
V
i
nnnn
nn
nn
''
'
',
||''||)()(
2D electron+Rashba 2D holes+Rashba
Prediction: one should observe strong intrinsic SHE in 2D hole systems
Nomura et al PRB 05
OUTLINEOUTLINE From electronics to spintronics:From electronics to spintronics:
Electron multipersonality: using the charge and using the Electron multipersonality: using the charge and using the spinspin
Success stories of metal based spintronicsSuccess stories of metal based spintronics Why semiconductor spintronics may be betterWhy semiconductor spintronics may be better Spin-orbit coupling: the necessary evilSpin-orbit coupling: the necessary evil The usual example: Das-Datta transistorThe usual example: Das-Datta transistor
Spin-Hall effect: Spin-Hall effect: Normal and anomalous Hall effect and Spin Hall effect Normal and anomalous Hall effect and Spin Hall effect
Three contributions to the AHEThree contributions to the AHE Turbulent history of the AHETurbulent history of the AHE Recent focus on the intrinsic AHERecent focus on the intrinsic AHE Application to the SHEApplication to the SHE Short but turbulent history of the SHEShort but turbulent history of the SHE
SHE experimentsSHE experiments Resolution of some of the controversyResolution of some of the controversy Spin Hall spin accumulationSpin Hall spin accumulation Theory challengesTheory challenges Experimental challengesExperimental challenges
First experimentalFirst experimental observations at the end of 2004observations at the end of 2004
Wunderlich, Kästner, Sinova, Jungwirth, cond-mat/0410295PRL 05
Experimental observation of the spin-Hall effect in a two dimensional spin-orbit coupled semiconductor system
Co-planar spin LED in GaAs 2D hole gas: ~1% polarization Co-planar spin LED in GaAs 2D hole gas: ~1% polarization
-1
0
1
CP
[%]
Light frequency (eV)1.505 1.52
Kato, Myars, Gossard, Awschalom, Science Nov 04
Observation of the spin Hall effect bulk in semiconductors
Local Kerr effect in n-type GaAs and InGaAs: Local Kerr effect in n-type GaAs and InGaAs: ~0.03% polarization ~0.03% polarization (weaker SO-coupling, stronger disorder)(weaker SO-coupling, stronger disorder)
p -AlG a As
i-G a As
n- -d o p e d AlG a As
e tc he d
QW
I
Top Emission
Side Emission
Electrode
Spin polarization detected through circular polarization of emitted lightSpin polarization detected through circular polarization of emitted light
ConventionalConventional vertical spin-LEDvertical spin-LED Novel dual Novel dual co-planar spin-LEDco-planar spin-LED
Y. Ohno: Nature 402, 790 (1999) R. Fiederling: Nature 402, 787 (1999)
● SHE in 2DHG with strong and tunable SO● SHE detected directly in the 2DHG● Light emission near edge of the 2DHG● No hetero-interface along the LED current
2DHG2DHG
2DEG2DEG
How our experiment worked: creating a spin-meter at edges
1 .5 mc h a n n e l
n
n
py
xz
L E D 1
L E D 2
I P+Ip
E [eV]
a
-1
0
1
LED 1
-Ip
CP
[%]
a
Opposite perpendicular polarization for opposite Opposite perpendicular polarization for opposite IIpp currents currents
or opposite edges or opposite edges SPIN HALL EFFECT SPIN HALL EFFECT
xy
zIp
-Ip
ILED 1
Experiment “A”
xy
zIpILED 1
ILED 2
Experiment “B”
1.505 1.510 1.515 1.520
-1
0
1
+Ip LED 1
LED 2b
CP
[%]
OTHER RECENT EXPERIMENTS
“demonstrate that the observed spin accumulation is due to a transverse bulk electron spin current”
Sih et al, Nature 05, PRL 05
Valenzuela and Tinkham cond-mat/0605423, Nature 06
Transport observation of the SHE by spin injection!!
Saitoh et al APL 06
Next: solving some of the SHE Next: solving some of the SHE controversycontroversy
• Does the SHE conductivity vanish due to scattering? Seems to be the case in 2DRG+Rashba,
does not for any other system studied
• Dissipationless vs. dissipative transport
• Is the SHE non-zero in the mesoscopic regime?
• What is the best definition of spin-current to relate spin-conductivity to spin accumulation
•……
APCTP Workshop on Semiconductor APCTP Workshop on Semiconductor Nano-Spintronics: Spin-Hall Effect and Related IssuesNano-Spintronics: Spin-Hall Effect and Related Issues
August 8-11, 2005 APCTP, Pohang, Korea August 8-11, 2005 APCTP, Pohang, Korea
http://faculty.physics.tamu.edu/sinova/SHE_workshop_APCTP_05.html
A COMMUNITY WILLING TO WORK TOGETHER
Semantics agreement:The intrinsic contribution to the spin Hall conductivity is the spin Hall conductivity in the
limit of strong spin orbit coupling and >>1. This is equivalent to the single bubble contribution to the Hall conductivity in the weakly scattering regime.
General agreement•The spin Hall conductivity in a 2DEG with Rashba coupling vanishes in the absence of a magnetic field and spin-dependent scattering. The intrinsic contribution to the spin Hall conductivity is identically cancelled by scattering (even weak scattering). This unique feature of this model can be traced back to the specific spin dynamics relating the rate of change of the spin and the spin current directly induced, forcing such a spin current to vanish in a steady non-equilibrium situation.
•The cancellation observed in the 2DEG Rashba model is particular to this model and in general the intrinsic and extrinsic contributions are non-zero in all the other models studied so far. In particular, the vertex corrections to the spin-Hall conductivity vanish for p-doped models.
The new challenge: understanding spin accumulation
Spin is not conserved; analogy with e-h system
Burkov et al. PRB 70 (2004)
Spin diffusion length
Quasi-equilibrium
Parallel conduction
Spin Accumulation – Weak SO
Spin Accumulation – Strong SO
Mean FreePath?
Spin Precession
Length
?
SPIN ACCUMULATION IN 2DHG: EXACT DIAGONALIZATION
STUDIES
so>>ħ/
Width>>mean free path
Nomura, Wundrelich et al PRB 06
Key length: spin precession length!!Independent of !!
-1
0
1
Pol
ariz
atio
n in
%
1.505 1.510 1.515 1.520
-1
0
1
Energy in eV
Pol
ariz
atio
n in
%
1.5mchannel
n
n
py
xz
LED1
LED2
10m channel
SHE experiment in SHE experiment in GaAs/AlGaAs 2DHGGaAs/AlGaAs 2DHG
- shows the basic SHE symmetries
- edge polarizations can be separated over large distances with no significant effect on the magnitude
- 1-2% polarization over detection length of ~100nm consistent with theory prediction (8% over 10nm accumulation length)
Wunderlich, Kaestner, Sinova, Jungwirth, Phys. Rev. Lett. '05
Nomura, Wunderlich, Sinova, Kaestner, MacDonald, Jungwirth, Phys. Rev. B '05
Theoretical achievements:
Theoretical challenges:GUT the bulk (beyond simple graphene)
intrinsic + extrinsic SHE+AHE+AMR
Obtain the same results for different equivalent approaches (Keldysh and Kubo must agree)
Othersmaterials and defectscoupling with the latticeeffects of interactions (spin Coulomb drag)spin accumulation -> SHE conductivity
Intrinsic SHEback to the beginning on a higher level
2003 2006Extrinsic SHE
approx microscopic modelingExtrinsic + intrinsic AHE in graphene:
two approaches with the same answer
WHERE WE ARE GOING (THEORY)
Experimental achievements
Experimental (and experiment modeling) challenges:
Photoluminescence cross sectionedge electric field vs. SHE induced spin accumulationfree vs. defect bound recombinationspin accumulation vs. repopulationangle-dependent luminescence (top vs. side emission)hot electron theory of extrinsic experiments
Optical detection of current-induced polarizationphotoluminescence (bulk and edge 2DHG)Kerr/Faraday rotation (3D bulk and edge, 2DEG)
Transport detection of the SHE
Generaledge electric field (Edelstein) vs. SHE induced spin accumulation
SHE detection at finite frequenciesdetection of the effect in the “clean” limit
WHERE WE ARE GOING (EXPERIMENTS)
Branislav NikolicU. of DelawareAllan MacDonald
U of Texas
Tomas JungwirthInst. of Phys. ASCR
U. of Nottingham
Joerg WunderlichCambridge-Hitachi
Laurens MolenkampWuerzburg
Kentaro NomuraU. Of Texas
Ewelina HankiewiczU. of MissouriTexas A&M U.
Mario BorundaTexas A&M U.
Nikolai SinitsynTexas A&M U.
U. of Texas
Other collaborators: Bernd Kästner, Satofumi Souma, Liviu Zarbo, Dimitri Culcer , Qian Niu, S-Q Shen, Brian Gallagher, Tom Fox, Richard Campton, Winfried Teizer, Artem Abanov
Sergio RodriguezTexas A&M U.
Xin LiuTexas A&M U.
Alexey KovalevTexas A&M U.
NERC
2D spin-LED
2DHG 2DEG 2DHG
2DEG VT
VD
Light emitted comes from Type II recombination processes: 3D electrons with 2D holes. 3D electrons have an asymmetric momentum space population (e.g. ky>0)
Measurement of 2DHG Rashba
splitting
Spin-Hall effect measrement
Sub GaAs gap spectra analysis: EL vs PLSub GaAs gap spectra analysis: EL vs PL
X : bulk GaAs excitons
I : recombinationwith impurity states
1.48 1.49 1.50 1.51 1.520
2
4
6
8
10
0
2
4
6
8
10
Wafer 1
0 -50 -100 -150-2
-1
0
1
2
Wafer 2
Int [a.u
.]
E [eV]
E [
eV]
p-AlGaAs
n-AlGaAs
GaAs/AlGaAs superlatticeGaAs substrate
etched
2DEG2DHG
i-GaAs
y
z GaAsp-AlGaAs
n-AlGaAs
GaAs/AlGaAs superlatticeGaAs substrate
etched
2DEG2DHG
i-GaAs
y
z GaAs
z [nm]
a
b
c
d
I
X
I
X
A
A
A
A
B
B
B
B
C
C
PLEL
p-AlGaAs
GaAs
BB ( (A,CA,C): ): 3D electron – 3D electron –
2D hole 2D hole recombinationrecombination
OUTLINEOUTLINE Metal and semiconductor based spintronicsMetal and semiconductor based spintronics Spin-orbit coupling in semiconducting systemsSpin-orbit coupling in semiconducting systems Hall effect, Anomalous Hall effect, and Spin Hall Hall effect, Anomalous Hall effect, and Spin Hall
effecteffect Ordinary and quantum Hall effectOrdinary and quantum Hall effect Anomalous Hall effect and spin Hall effect (SHE)Anomalous Hall effect and spin Hall effect (SHE) Intrinsic SHE in Rashba SO couple systems Intrinsic SHE in Rashba SO couple systems
Optical detection of the polarizationOptical detection of the polarization Our measuring technique: LED probe of Our measuring technique: LED probe of
polarizationpolarization Lateral 2DEG-2DHG junctionLateral 2DEG-2DHG junction Comparison of electro-luminescence and photo-Comparison of electro-luminescence and photo-
luminescenceluminescence Measurement of the SO splitting: in-plane Measurement of the SO splitting: in-plane
polarization through asymmetric recombinationpolarization through asymmetric recombination SHE measurementSHE measurement Conclusions and outlookConclusions and outlook
Light polarization due to recombination with SO-split Light polarization due to recombination with SO-split hole-subband in a p-n LED under hole-subband in a p-n LED under forwardforward bias bias
spin operators of holes: j=3s
-0.2 0.0 0.2-0.50
-0.25
0.00
0.25
0.50
<sx>HH+
<sx>HH-
<sz>HH--
<s<szz>>HHHH++
<S
>
ky [nm-1]
spin-polarization of HH+ and HH- subbands
in-planein-plane polarization
s=1/2 electrons to j=3/2 holes plus selection rules
circular polarization of emitted light
Microscopic band-structure calculations of the 2DHG:
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
ky [nm-1]
3D electron-2D hole Recombination
-0.2 0.0 0,2
0
20
NO perp.-to-plane component of polarization at B=0NO perp.-to-plane component of polarization at B=0
BB≠0 behavior consistent with SO-split HH subband≠0 behavior consistent with SO-split HH subband
1.500 1.505-20
-10
0
10
20
Bz = +3T
Bz = -3T-10
-5
0
5
10
Bx = +3T
Bx = -3T
E [eV]-3 -2 -1 0 1 2 3
xy
z , B
xy
z , B
B [T]
x, By
z
x, By
z
x, By
α
x, By
z
x, By
z
x, By
x, By
z
x, By
z
x, By
z
x, By
α
CP
[%]
1.500 1.505-20
-10
0
10
20
Bz = +3T
Bz = -3T-10
-5
0
5
10
Bx = +3T
Bx = -3T
E [eV]-3 -2 -1 0 1 2 3
xy
z , B
xy
z , B
B [T]
x, By
z
x, By
z
x, By
α
x, By
z
x, By
z
x, By
x, By
z
x, By
z
x, By
z
x, By
α
CP
[%]
In-plane
detection angle/polarization
Perp.-to plane
detection angle/polarization
20m
n
p Jun
ction
y
xz
20m
n
p Jun
ction
y
xz