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 1m1m 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