detection of current induced spin polarization with a co-planar spin led j. wunderlich (1), b....
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![Page 1: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/1.jpg)
Detection of current induced Spin polarization with a co-planar spin LED
J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5)
(1) Hitachi Cambridge Laboratory, UK
(2) National Physical Laboratory, UK
(3) Texas A&M University, USA
(4) Institute of Physics ASCR, Czech Republic
(5) University of Nottingham, UK
Thanks to A.H. MacDonald, University of Texas
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- Current induced spin-polarization:
Levitov, Mal’shukov, Spin-Hall
- Experimental results
- Conclusion / Outlook
OUTLINEOUTLINE
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- by asymmetrical optical recombination in a pn-junction
- by applying an electric field Ex
x
y
z x
y
z x
y
z
Ex = 0
kx
ky Ex > 0
Sy
Ex = 0
kx
ky Ex > 0
Ex = 0
kx
ky Ex > 0
Sy
x
y
z x
y
z x
y
z x
y
z x
y
z x
y
z
Ex = 0
kx
ky Ex > 0
Sy
Ex = 0
kx
ky Ex > 0
Ex = 0
kx
ky Ex > 0
Sy
[Mal’shukov et al., PRB 65 241308(R) (2002)][Levitov et al , Zh. Eksp. Teor. Fiz. 88, 229 (1985)]
InplaneInplane polarization for a [001] grown GaAs quantum well
““Levitov effect” “Mal’shukov effect”Levitov effect” “Mal’shukov effect”
0
20
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
0
20
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
-0.2 0.0 0,2
ky [nm-1]
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Spin Hall effectSpin Hall effect
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 accumulationexcludes simple electrical detection
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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
Conventional vertical spin-LED
Novel co-planar spin-LED
Y. Ohno et al.: Nature 402, 790 (1999)
R. Fiederling et al.: Nature 402, 787 (1999)
B. T. Jonker et al.: PRB 62, 8180 (2000)
X. Jiang et al.: PRL 90, 256603 (2003)
R. Wang et al.: APL 86, 052901 (2005)
…
● Light emission near edge of the 2DHG
● 2DHG with strong and tunable SO
● Spin detection directly in the 2DHG
● No hetero-interface along the LED current
2DHG2DHG
2DEG2DEG
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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
Conventional vertical spin-LED
Novel co-planar spin-LED
Y. Ohno et al.: Nature 402, 790 (1999)
R. Fiederling et al.: Nature 402, 787 (1999)
B. T. Jonker et al.: PRB 62, 8180 (2000)
X. Jiang et al.: PRL 90, 256603 (2003)
R. Wang et al.: APL 86, 052901 (2005)
…
● No hetero-interface along the LED current
● Spin detection directly in the 2DHG
● Light emission near edge of the 2DHG
● 2DHG with strong and tunable SO
2DHG2DHG
2DEG2DEG
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p-AlGaAs
i-GaAs
n--doped AlGaAs n- -doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
etched
n--doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs n- -doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
etched
n--doped AlGaAs
-200
-100
0
-2 -1 0 1 2
p EF
p, n [1018
/cm3]
VB CB
Energy [eV]
z [n
m]
0 1 2
p-AlGaAs
i-GaAs
n--doped AlGaAs n- -doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
etched
n--doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs n- -doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
etched
n--doped AlGaAs
-2 -1 0 1 2-200
-100
0
p, n [1018
/cm3]
VB CB
z [n
m]
Energy [eV]
0 1 2
EF
n
Wafer design based on Schrödinger-Poisson simulations
CO-PLANAR CO-PLANAR pn pn - JUNCTION- JUNCTION
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n - region p - region
Carrier density: n = 0.8 1012 cm-2 p = 2.0 1012 cm-2
Mobility: µHn 2900 cm2/Vs µHp 3400 cm2/Vs
pn - junction● Rectifying ● Light emission for e VBias EG
● Light emission near junction in p-region
np10 µm
6 8 10 12
-100
-50
0
50
100
150
B [T]
0.0
0.5
1.0
1.5
2.0
R2P
-qu
adra
tic
fit
[]
RH
all [
k]
0 2 4 6 8 104
6
8
10
12
B [T]
0
2
4
6
8
10R
2P [
k]
RH
all [
k]
-12 -10 -8 -6 -4 -2 0 2
0.0
0.2
0.4
0.6
0.8
Bia
s C
urre
nt in
A
Bias Voltage in V
Reverse breakdown:VR = -11.5V (T = 4.2K)
0.0 0.5 1.0 1.5 2.0
1E-11
1E-9
1E-7
1E-5
1E-3
300K 4.2K
Cur
rent
[A]
Voltage [V]
Light emission
● 2D transport characteristics
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-150
-100
-50
0
-2 -1 0 1 2
p-AlGaAs
i-GaAs
n--doped AlGaAs n- -doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
etched
n--doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs n- -doped AlGaAs
p-AlGaAs
i-GaAs
n--doped AlGaAs
etched
n--doped AlGaAs
p -AlGaAs
GaAs
1m
z [n
m]
Energy [eV]
E
z
Electron – 2D holes recombination
possible
-150
-100
-50
0
-2 -1 0 1 2
-+
Band-flattening if forward biased
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0 -50 -100 -150-2
-1
0
1
2
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]
0
2
4
6
8
10
Wafer 1
Wafer 2
Int
[a.u.]
E [eV]1.48 1.49 1.50 1.51 1.52
0
2
4
6
8
10
I
X
I
X
PL
p-AlGaAs
GaAs
0 -50 -100 -150-2
-1
0
1
2
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]
0
2
4
6
8
10
Wafer 1
Wafer 2
Int
[a.u.]
E [eV]1.48 1.49 1.50 1.51 1.52
0
2
4
6
8
10
I
X
I
X
PL
0
2
4
6
8
10
Wafer 1
Wafer 2
Int
[a.u.]
E [eV]1.48 1.49 1.50 1.51 1.52
0
2
4
6
8
10
I
X
I
X
PL
p-AlGaAs
GaAs
Sub GaAs gap spectra analysis: PL vs EL
X : bulk GaAs excitons
I : recombinationwith impurity states
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Sub GaAs gap spectra analysis: PL vs EL
Wafer 1
0 -50 -100 -150-2
-1
0
1
2
Wafer 2
Int
[a.u.]
E [eV]
E [
eV]
0
2
4
6
8
10
1.48 1.49 1.50 1.51 1.520
2
4
6
8
10
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]
I
X
I
X
A
A
B
B
C
PLEL
p-AlGaAs
GaAs
X : bulk GaAs excitons
I : recombinationwith impurity states
BB ( (A,CA,C): ): 3D electron – 3D electron – 2D hole 2D hole recombinationrecombination
+-
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Wafer 1
0 -50 -100 -150-2
-1
0
1
2
Wafer 2
Int
[a.u.]
E [eV]
E [
eV]
0
2
4
6
8
10
1.48 1.49 1.50 1.51 1.520
2
4
6
8
10
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]
I
X
I
X
A
A
A
A
B
B
B
B
C
C
PLEL
p-AlGaAs
GaAs
Sub GaAs gap spectra analysis: PL vs EL
X : bulk GaAs excitons
I : recombinationwith impurity states
BB ( (A,CA,C): ): 3D electron – 3D electron – 2D hole 2D hole recombinationrecombination
Bias dependent emission wavelength for 3D electron – 2D hole Bias dependent emission wavelength for 3D electron – 2D hole recombination recombination [A. Y. Silov et al., APL 85, 5929 (2004)][A. Y. Silov et al., APL 85, 5929 (2004)]
++--
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EXPERIMENT
2DHG 2DEG
Occupation-asymmetry mostly due to
“Mal’shukov effect”
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Light polarization due to recombination with SOLight polarization due to recombination with SO--split split holehole--subbandsubband in a in a pp--nn LED under forward biasLED under forward 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--
<<sszz>>HHHH++
<S
>
ky [nm-1]
spin-polarization of HH+ and HH- subbands
-0.2 0.0 0.2-0.50
-0.25
0.00
0.25
0.50
-0.2 0.0 0.2-0.50
-0.25
0.00
0.25
0.50
<sx>HH+
<sx>HH-
<sz>HH--
<<sszz>>HHHH++
<S
>
ky [nm-1]
spin-polarization of HH+ and HH- subbands
inin--planeplane polarization
0
20
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
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
ky [nm-1]
3D electron-2D hole Recombination
0
20
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
ky [nm-1]
0
20
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
0
20
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
0
20
E [
meV
]
a
HH+
HH-LH
- +
-20
0
20
ky [nm-1]
3D electron-2D hole Recombination
-0.2 0.0 0,2
s=1/2 electrons to j=3/2 holes plus selection rules
circular polarization of emitted light
Microscopic band-structure calculations of the 2DHG:
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12.00 12.05 12.10 12.15 12.20 12.25 12.30
0
1
2
3
4
5
6
7
1.488 1.494 1.500 1.506 1.513 1.519 1.525
[eV]
EL
inte
nsi
ty [
a.u
.]
energy [103 cm
-1]
-5.0
-2.5
0.0
2.5
5.0
Deg
ree of C
ircular p
olarizatio
n [%
]
Circular Polarization of EL detected at perpendicular to 2DHG plane
z
j
z
j
z
j
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-10
-5
0
5
10
Deg
ree of C
ircular p
olarizatio
n [%
]
12.00 12.05 12.10 12.15 12.20 12.25 12.30
0
1
2
3
4
5
6
1.488 1.494 1.500 1.506 1.513 1.519 1.525
[eV]
EL
inte
nsi
ty [
a.u
.]
energy [103 cm
-1]
Inplane Circular Polarization (= 85º) detected at B = + 3T.
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-10
-5
0
5
10
Deg
ree of C
ircular p
olarizatio
n [%
]
12.00 12.05 12.10 12.15 12.20 12.25 12.30
0
1
2
3
4
5
6
1.488 1.494 1.500 1.506 1.513 1.519 1.525
[eV]
EL
inte
nsi
ty [
a.u
.]
energy [103 cm
-1]
Inplane Circular Polarization (= 85º) detected at B = 3T.
Wafer 1
Int
[a.u.]
E [eV]
0
2
4
6
8
10
0
2
4
6
8
10I
XA B
PLEL
1.48 1.50 1.52
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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
Circular Polarization
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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
[%]
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
In-plane
detection angle
Perp.-to plane
detection angle
Circular Polarization
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j
SHE
Spin Hall Effect Spin Hall Effect
Perpendicular-to-plane spin-polarization
![Page 21: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/21.jpg)
EXPERIMENT
Spin Hall Effect
2DHG
2DEG VT
VD
![Page 22: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/22.jpg)
Spin Hall Effect Device
1 .5 mc h a n n e l
n
n
py
xz
L E D 1
L E D 2
I P
xy
zIp
-Ip
ILED 1
Experiment “A”
xy
zIpILED 1
ILED 2
Experiment “B”
![Page 23: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/23.jpg)
Experiment “B”
1.505 1.510 1.515 1.520
-1
0
1
xy
zIpILED 1
ILED 2
CP
[%]
1.505 1.510 1.515 1.520
-1
0
1
xy
zIpILED 1
ILED 2
xy
zIpILED 1
ILED 2
CP
[%]
Experiment “A”
-1
0
1
xy
zIp
-Ip
ILED 1
CP
[%]
-1
0
1
xy
zIp
-Ip
ILED 1
-1
0
1
xy
zIp
-Ip
ILED 1
xy
zIp
-Ip
ILED 1
CP
[%]
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
![Page 24: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/24.jpg)
Comparing extrinsic and intrinsic SHE contribution for our system by taking HH mass and mobility in account:
-within the intrinsic SHE regime- larger contribution from intrinsic SHE
![Page 25: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/25.jpg)
Changing confinement, charge carrier density, via gating, wafer design, temperature dependence,etc.
Outlook
2DHG
2DEG
2DEG GATEGATE jpn
GATEGATE j
SHE in with differently confined 2DHG
2DHG
2DHG
2DEG
SHE in 2DHG and 2DEG
![Page 26: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/26.jpg)
n
p2 0 m
MMM
ex tB
M
Before
and
after an in-planemagnetic field was applied
Stray-field into the inversion layer
Expect field strength at2DEG of approx. 0.1 –0.2 T
12.15 12.20 12.25 12.30
1.506 1.513 1.519 1.525
[eV]
energy [103 cm-1]
0.0
1.0
Circu
lar po
larization
[%]
[T]B
[nm]z[nm]x
z
M
x
d
z
M
x
z
M
x
dd = 50 nm
[T]B
[nm]z[nm]x
z
M
x
d
z
M
x
z
M
x
dd = 50 nm
z
M
x
d
z
M
x
z
M
x
dd = 50 nm
[T]B
[nm]z[nm]x
z
M
x
d
z
M
x
z
M
x
dd = 50 nm
[T]B
[nm]z[nm]x
z
M
x
d
z
M
x
z
M
x
dd = 50 nm
z
M
x
d
z
M
x
z
M
x
dd = 50 nm
[T]B [T]B [T]B
[nm]z [nm]z [nm]z[nm]x [nm]x [nm]x
z
M
x
d
z
M
x
z
M
x
dd = 50 nm
z
M
x
d
z
M
x
z
M
x
d
z
M
x
z
M
M
x
d
z
M
x
z
M
x
d
z
M
M
x
z
M
M
x
dd = 50 nm
[T]B [T]B [T]B
[nm]z [nm]z [nm]z[nm]x [nm]x [nm]x
z
M
x
d
z
M
x
z
M
x
d
z
M
x
z
M
M
x
d
z
M
x
z
M
x
d
z
M
M
x
z
M
M
x
dd = 50 nm
z
M
x
d
z
M
x
z
M
x
d
z
M
x
z
M
M
x
d
z
M
x
z
M
x
d
z
M
M
x
z
M
M
x
dd = 50 nm
magnetic particle on top of 2DEG channel
MFM micrograph
Locally induced Electron spin polarizationLocally induced Electron spin polarization
![Page 27: Detection of current induced Spin polarization with a co-planar spin LED J. Wunderlich (1), B. Kästner (1,2), J. Sinova (3), T. Jungwirth (4,5) (1)Hitachi](https://reader035.vdocuments.site/reader035/viewer/2022062809/5697bf921a28abf838c8f0b6/html5/thumbnails/27.jpg)
Conclusion
• Spin polarization due to occupation-asymmetryDetection of in-plane net-spin-polarization
• spin-Hall effect in hole systemDetection of perpendicular-to-plane polarization