Transcript Slide 1
From ferromagnetic to non-magnetic semiconductor spintronics: Spin-injection Hall effect
Tomas Jungwirth
Institute of Physics ASCR
Jairo Sinova, Karel Výborný, Jan Zemen, Jan Ma šek, Alexander Shick, František Máca, Jorg Wunderlich, Vít Novák, Kamil Olejník, et al.
Hitachi Cambridge, Univ. Cambridge
Jorg Wunderlich, Andrew Irvine, Byonguk Park, et al.
University of Nottingham
Bryan Gallagher, Richard Campion, Kevin Edmonds, Andrew Rushforth, et al.
Texas A&M University
Jairo Sinova, Liviu Zarbo, et al.
AMR and GMR (TMR) sensors: dawn of spintronics Inductive read elements Magnetoresistive read elements
1980’s-1990’s
Ferromagnetism & spin-orbit coupling
anisotropic magnetoresistance
~ 1% MR effect
Ferromagnetism only
giant (tunnel) magnetoresistance
~ 100% MR effect
magnetization current
Lord Kelvin 1857 Fert, Grunberg et al. 1988
Renewed interest in SO induced MRs in ferromagnetic semiconductors
Ohno Science ’98
~ 1000% MR effect & gate controlled
Wunderlich et al. PRL ’06 Schlapps et al. PRB `09
Coulomb blockade AMR: likely the most sensitive spintronic transistors to date p- or n-type FET depending on magnetization
non-volatile programmable logic, etc.
SO induced MRs: AMR & anomalous Hall effect
Ordinary Hall effect
: response in normal metals to external magnetic field via Lorentz force Hall 1879
B
_ F L
I
Anomalous Hal effect
: response to internal spin polarization in ferromagnets via spin-orbit coupling Hall 1881
M
F SO
I V V
T c in (Ga,Mn)As upto ~190 K but AHE survives and dominates HE far above T c OHE AHE
Ruzmetov et al. PRB ’04
(Ga,Mn)As: simple band structure of the host SC j=3/2 HH
HH & LH Fermi surfaces
Quantitative AHE theory
Jungwirth et al. PRL ’02
Spherical HH Kohn-Luttinger 3D model Rashba and Dresselhaus 2D models
Intense theory research of AHE in model 2D R&D systems
H SO
1
mc
2
S
e v
E Nagaosa et al RMP ‘’09 in press (arXiv:0904.4154)
Taming spins in non-magnetic materials: spin-Hall effect
Ordinary Hall effect
: response in normal metals to external magnetic field via classical Lorentz force Hall 1879
B
_ F L
I
Anomalous Hal effect
: response to internal spin polarization in ferromagnets via quantum-relativistic spin-orbit coupling Hall 1881
F SO
M I V V Spin Hall effect spin-dependent deflection transverse edge spin polarization
F SO _ F SO
Wunderlich et al. arXives ’04 (PRL ’05) Kato et al. Science ’04
I
||
E
Polarized EL from a planar LED Theory and experiment: ~10% polarization over ~10nm wide edge region
More taming of spins by spin-orbit coupling
Spin-injection from a ferromagnet
Wunderlich et al. Nature Phys.‘09
+
More 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 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 coupling
Spin-injection Hall effect +
+ + + + + + + + + + + + – – – – – – – – – – – –
Spin-dependent deflection due to spin-orbit coupling transverse (Hall)
electrical voltage
in steady state
Wunderlich et al. Nature Phys.‘09
More 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 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 coupling
Spin-injection Hall effect
V G
+ + – – + + – – + + – – + + – – + + – –
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
Optical injection of spin-polarized charge currents into Hall bars
GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell
e V H e e e e e h h h h h h
2DEG 2DHG
V b 2DHG 2DEG
h h
Optical spin-generation area near the p-n junction
Simulated band-profile
V H2 V L
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 1 m from the p-n junction safely outside the spin-generation area and/or masked Hall probes
Experimental observation of the SIHE
SIHE linear in degree of polarization and spatially varying
Spin dynamics in Rashba&Dresselhaus SO-couped 2DEG
H
2DEG
2
k
2 2
m
k y
x
k x
y
k x
x
k y
y
> 0, = 0 = 0, < 0
k-
dependent SO field strong precession & spin-decoherence due to scattering
[110]
No decoherence for
|
| = |
| & channel
SO field
L
[ 1 10 ] 4
k
[ 1 10 ]
t k
[ 1 10 ]
t
/ /
m Bernevig et al PRL’06
[1-10]
Diffusive spin dynamics & Hall effect due to skew scattering
H
2DEG 2
k
2 2
m
k y
x
k x
y
k x
x
k y
y
* (
k
V dis (
r
)) precession-length (~1 m) >> mean-free-path (~10 nm)
H
(
x
[ 1 1 0 ] ) 2 *
e
n i
n p z
(
x
[ 1 1 0 ] )
p Z
(
x
[ 1 1 0 ] ) exp[
q x
[ 1 1 0 ] ]
q
|
q
| exp(
i
) , |
q
| ( ~
L
1 2 ~
L
2 2 ~
L
2 4 ) 1 4 ~
L
1 / 2 1 2 arctan 2
m
| ~
L
2 1 ~
L
2 2 ~
L
2 2 | ~
L
1 2 ~
L
1 4 2 2 4
Conclusions
SIHE: high-T SO only spintronics in non-magnetic systems 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)
SIHE vs other spin-detection tools in semiconductors
Crooker et al. JAP’07, others
Magneto-optical imaging
non-destructive lacks nano-scale resolution and only an optical lab tool
Ohno et al. Nature’99, others
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
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