from ferromagnetic to non-magnetic semiconductor spintronics: spin-injection hall effect
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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
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