1 / 22

Optical study of Spintronics in III-V semiconductors

Optical study of Spintronics in III-V semiconductors. Xiaodong Cui University of Hong Kong. Collaborators. Spin Dynamics • Magneto-photocurrent Dr. Yang Chunlei Mr. Dai Junfeng Theorist: Dr. Lu Hai-Zhou Prof. Shen Shun-Qing Prof. Zhang Fu-Chun. Outline.

gari
Download Presentation

Optical study of Spintronics in III-V semiconductors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Optical study of Spintronics in III-V semiconductors Xiaodong Cui University of Hong Kong

  2. Collaborators • Spin Dynamics • Magneto-photocurrent Dr. Yang Chunlei Mr. Dai Junfeng Theorist: Dr. Lu Hai-Zhou Prof. Shen Shun-Qing Prof. Zhang Fu-Chun

  3. Outline • Time resolved Kerr-rotation spectroscopy in the Spin dynamics study • Spin Photocurrent in two dimensional electron gases of InGaAs

  4. Kerr Rotation spectroscopy Classical picture: Change in the polarization state when a linearly polarized light reflected from a strong magnet. Magnetization ↔Bound currents boundary conditions E M

  5. Microscopic origin – selection rule mj=-1/2 mj=+1/2 2 1 3 -1/2 +1/2 mj=-3/2 mj=+3/2 mj=-1/2 mj=+1/2 Pump beam: Creating Spin Polarization via Optical injection. Probe beam: A linearly polarized light is a superposition of a left and right circularly Polarized lights.

  6. M2 Ti:Sapphire M1 I1 I2 M4 M3 I3 I4 YAG PBS1 M5 M6 M7 PEM Chopper M8 Pump M9 Sample M10 BS1 Probe /2 Plate f1 f2 L3 BS2 L5 M11 PBS2 L4 DET LA1 LA2 DET: Twin detector I: Iris M: Mirror L: lens PBS: polarized beam splitter LC: lock-in amplifier

  7. g-factor Existing techniques to study g factor: • Electric transport Low temperature, high requirements for sample quality • Electron spin resonance unpaired electron • Magneto-photoluminescence complex origins, signal reflects information of exciton • Kerr-rotation spectroscopy Magnitude, NO sign information

  8. g factor study by Kerr rotation spectroscopy z y x Torque driving precession Spin projection along Z

  9. (a) GaAs thin film g=-0.42 (T=5K) (b) GaAs 2DEG g=-0.36 (T=5K) (c) GaAsN/GaAs quantum well (N~1.5%) g=+0.97

  10. GaAsN/GaAs quantum well Phase shift is determined by the experimental configuration  For g>0 Phase term gBBt/ħ+ for B>0 gBBt/ħ- for B<0

  11. Another Approach – magnetic field scan at fixed time delay Magnetic field shift is determined by the experimental configuration  • Advantage against time scan: • time shift in time scan ~ ps • magnetic shift in field scan ~ 102-103 Gauss

  12. Electric current and spin current The electric current The spin current

  13. Generation of Spin current • Spin injection • Spin polarized charge current • Non-local spin injection • Optical injection Intra-band Linearly polarized light: • Ganichev et al., Nature Physics 2, 609 (2006). • Inter-band Linearly polarized light (one photon, two photon): • H. Zhao et al., PHYSICAL REVIEW B 72, 201302 2005; Phys. Rev. Lett. 96, 246601 (2006). • Bhat et al., Phys. Rev. Lett. 85, 5432 (2000). • Spin pumping (ferromagnetic resonance) • Spin Hall effect

  14. Generation and Detection of Spin current -- Spin Hall effect Converting to charge current Converting to magnetization Valenzuela, S. O. & Tinkham, M. Nature 442, 176–179 (2006). Awschalom, Science 306, 1910–1913 (2004) Kimura, Phys. Rev. Lett, 98, 156601 (2007) Wunderlich; Phys. Rev. Lett. 94, 047204 (2005) Wunderlich, Nature Physics, 5,675 (2009)

  15. Zero-bias spin separation Ganichev et al., Nature Physics 2, 609 (2006). Intra-band excitation with linearly polarized THz radiation Spin dependent excitation and relaxation process

  16. (001) C2V symmetry H=(xky- ykx) Incident light: 0.8eV Linearly polarized light (Band edge excitation) Rashba coefficient =4.3E10-12 eVm

  17. J(Bx, By, )= C0By + CxBxsin2 + CyBycos2

  18. (c)

  19. Estimate the spin current • Measurement of Photocurrent with Hall Effect J~ 1.5X10-2A/m at 1mW • Estimate the spin current from SdH oscillation • Estimate the ratio of field induced charge current Vs. zero field spin current

  20. The magnetic field induced charge current vs. pure spin current Magnetic field induced charge current density ~ Pure Spin photocurrent density(ħ) ~ The ratio ~ In our case, Fermi energy ~ 10-1~10 -2eV (n=9E11cm-1), Zeeman energy hu=1.2E-4 eV/Telsa (g= -0.4) The Ratio ~ 10-2 ~10-3 /Tesla

  21. Conclusion • Magnetic field induced photocurrent via direct inter-band transition by a linearly polarized light • Our experiments support that the spin photocurrent could be generated by linearly polarized light absorption in material with spin-orbit coupling. • The conversion of spin current to magnetic field induced photocurrent is around 10-2~10-3 per Tesla.

More Related