1. Institute of Physics ASCR Hitachi Cambridge, Univ. Cambridge
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.
Institute of Physics ASCR
Karel Výborný, Jan Zemen, Jan Mašek,
Vít Novák, Kamil Olejník, et al.
Hitachi Cambridge, Univ. Cambridge
Jorg Wunderlich, Andrew Irvine, Byonguk Park, et al.
Texas A&M
Jairo Sinova, et al.

2. AMR and GMR (TMR) sensors: dawn of spintronics
Inductive read elements
Magnetoresistive read elements
1980’s-1990’s

3. Ferromagnetism & spin-orbit coupling  anisotropic magnetoresistance
Ferromagnetism only
 giant (tunnel) magnetoresistance
~ 100% MR effect
~ 1% MR effect
magnetization
current
Lord Kelvin 1857
Fert, Grunberg et al. 1988

4. Renewed interest in SO induced MRs in ferromagnetic semiconductors
~ 1000% MR effect & gate controlled
Ohno Science ’98
Coulomb blockade AMR: likely the most sensitive spintronic transistors to date
Wunderlich et al. PRL ’06
Coulomb blockade oscillations in (Ga,MnAs) SET as a function of gate voltage and magnetization angle
Schlapps et al. arXiv:

5. I B M I V V SO induced MRs: AMR & anomalous Hall effect _ _ _
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 B
Hall 1879
Hall 1881 V _ M _ _
FSO _ FL I I V
Tc in (Ga,Mn)As upto ~190 K but AHE survives and dominates above room-T
Ruzmetov et al. PRB ’04

6. (Ga,Mn)As: simple band structure of the host SC
j=3/2 HH
HH & LH Fermi surfaces
Spherical HH Kohn-Luttinger 3D model  Rashba and Dresselhaus 2D models

7. Intense theory research of AHE in model 2D R&D systems
Nagaosa et al RMP ‘’09 in press (arXiv: )

8. Spin-injection Hall effect: SO-induced Hall effect of spin-polarized electrical current injected into non-magnetic system (2DEG)
– – – –
– – – –
jqs
nonmagnetic
Spin-polarizer
(e.g. ferromagnet,  light)
Wunderlich et al. Nature Phys.‘09
- spintronic effect in non-magnetic semiconductors based on SO only
 immediate prospect for high-T operation
- SO-induced Hall effect (like AHE) in the model 2D Rashba&Dresselhaus systems
- and more ….
- spin-detection tool of unique SO-induced spin dynamics effects in 2D systems
- directly applicable to a variety of opto-spintronic, spintronic transitor, etc. devices

9. Optical injection of spin-polarized charge currents into Hall bars
 GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell p
2DHG i n 9

10. Optical injection of spin-polarized charge currents into Hall bars
 GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell - p
2DHG i n 10

11. Optical injection of spin-polarized charge currents into Hall bars
 GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell i p n
2DHG
2DEG 11

12. Optical injection of spin-polarized charge currents into Hall bars
 GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell h h h h h h VH e e e e e e
2DHG
2DEG

13. 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 1m from the p-n junction
 safely outside the spin-generation area and/or masked Hall probes

14. Experimental observation of the SIHE

15. SIHE linear in degree of polarization and spatially varying

16. Spin dynamics in Rashba&Dresselhaus SO-couped 2DEG
 > 0,  = 0
 = 0,  < 0
k-dependent SO field  strong precession & spin-decoherence due to scattering

17. No decoherence for || = || & channel  SO field
Bernevig et al PRL’06
[110]
[1-10]

18. Diffusive spin dynamics & Hall effect due to skew scattering18

19.  lacks nano-scale resolution
SIHE vs other spin-detection tools in semiconductors
Magneto-optical imaging
non-destructive
 lacks nano-scale resolution
and only an optical lab tool
Crooker et al. JAP’07, others
MR Ferromagnet
 electrical
 requires semiconductor/magnet
hybrid design & B-field to orient
the FM
Ohno et al. Nature’99, others
spin-LED
 all-semiconductor
 requires further conversion of
emitted light to electrical
signal

20.  100-10nm resolution with current lithography
Spin-injection Hall effect
 non-destructive
 electrical
 nm resolution with current lithography
 in situ directly along the SC channel
& all-SC requiring no magnetic elements in the structure or B-field

21. 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
All-electric Datta-Das like transistor with Fe or (Ga,Mn)As spin-injectors,
top/bottom gate electrode, and SIHE detection