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
- Current induced spin-polarization: Levitov, Mal’shukov, Spin-Hall - Experimental results - Conclusion / Outlook OUTLINE
- by asymmetrical optical recombination in a pn-junction - by applying an electric field E x [Mal’shukov et al., PRB (R) (2002)] [Levitov et al, Zh. Eksp. Teor. Fiz. 88, 229 (1985)] Inplane Inplane polarization for a [001] grown GaAs quantum well “Levitov effect” “Mal’shukov effect” ,2 k y [nm -1 ]
Spin Hall effect like-spin Spin-orbit coupling “force” deflects like-spin particles I _ F SO _ _ _ V=0 non-magnetic Spin-current generation in non-magnetic systems without applying external magnetic fields Spin accumulation without charge accumulation excludes simple electrical detection
Spin 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, (2003) R. Wang et al.: APL 86, (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 2DHG 2DEG
Spin 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, (2003) R. Wang et al.: APL 86, (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 2DHG 2DEG
Wafer design based on Schrödinger-Poisson simulations CO-PLANAR pn - JUNCTION
n - regionp - region Carrier density: n = 0.8 cm -2 p = 2.0 cm -2 Mobility: µ Hn 2900 cm 2 /Vs µ Hp 3400 cm 2 /Vs pn - junction ● Rectifying ● Light emission for e V Bias E G ● Light emission near junction in p-region Reverse breakdown: V R = -11.5V (T = 4.2K) Light emission ● 2D transport characteristics
p - AlGaAs GaAs 1m1m z [nm] Energy [eV] E z Electron – 2D holes recombination possible - + Band-flattening if forward biased
Sub GaAs gap spectra analysis: PL vs EL X : bulk GaAs excitons I : recombination with impurity states
Sub GaAs gap spectra analysis: PL vs EL X : bulk GaAs excitons I : recombination with impurity states B (A,C): 3D electron – 2D hole recombination + -
Sub GaAs gap spectra analysis: PL vs EL X : bulk GaAs excitons I : recombination with impurity states B (A,C): 3D electron – 2D hole recombination Bias dependent emission wavelength for 3D electron – 2D hole recombination [A. Y. Silov et al., APL 85, 5929 (2004)] ++ --
EXPERIMENT 2DHG2DEG Occupation-asymmetry mostly due to “Mal’shukov effect”
Circular Polarization of EL detected at perpendicular to 2DHG plane
Inplane Circular Polarization ( = 85º) detected at B = + 3T.
Inplane Circular Polarization ( = 85º) detected at B = 3T.
In-plane detection angle Circular Polarization
NO perp.-to-plane component of polarization at B=0 B≠0 behavior consistent with SO-split HH subband In-plane detection angle Perp.-to plane detection angle Circular Polarization
j SHE Spin Hall Effect Perpendicular-to-plane spin-polarization
EXPERIMENT Spin Hall Effect 2DHG 2DEG VTVT VDVD
Spin Hall Effect Device Experiment “A” Experiment “B”
Experiment “A” Opposite perpendicular polarization for opposite I p currents or opposite edges SPIN HALL EFFECT
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
Changing confinement, charge carrier density, via gating, wafer design, temperature dependence,etc. Outlook 2DHG 2DEG GATE j p n j SHE in with differently confined 2DHG 2DHG 2DEG SHE in 2DHG and 2DEG
magnetic particle on top of 2DEG channel MFM micrograph Locally induced Electron spin polarization
Conclusion Spin polarization due to occupation-asymmetry Detection of in-plane net-spin-polarization spin-Hall effect in hole system Detection of perpendicular-to-plane polarization