Colossal enhancement of spin–orbit coupling in weakly hydrogenated graphene

Journal name:
Nature Physics
Volume:
9,
Pages:
284–287
Year published:
DOI:
doi:10.1038/nphys2576
Received
Accepted
Published online

Graphene’s extremely small intrinsic spin–orbit (SO) interaction1 makes the realization of many interesting phenomena such as topological/quantum spin Hall states2, 3 and the spin Hall effect4 (SHE) practically impossible. Recently, it was predicted1, 5, 6, 7 that the introduction of adatoms in graphene would enhance the SO interaction by the conversion of sp2 to sp3 bonds. However, introducing adatoms and yet keeping graphene metallic, that is, without creating electronic (Anderson) localization8, is experimentally challenging. Here, we show that the controlled addition of small amounts of covalently bonded hydrogen atoms is sufficient to induce a colossal enhancement of the SO interaction by three orders of magnitude. This results in a SHE at zero external magnetic fields at room temperature, with non-local spin signals up to 100; orders of magnitude larger than in metals9. The non-local SHE is, further, directly confirmed by Larmor spin-precession measurements. From this and the length dependence of the non-local signal we extract a spin relaxation length of ~1μm, a spin relaxation time of ~ 90ps and a SO strength of 2.5meV.

At a glance

Figures

  1. Device characterization.
    Figure 1: Device characterization.

    a, Scanning electron micrograph of a hydrogenated graphene sample showing multiple Hall bar junctions. Scale bar, 5μm. b, Measurement schematics for the non-local spin Hall measurement. Inset: schematics showing the deformation of the graphene hexagonal lattice due to hydrogenation. c, Evolution of the percentage of hydrogenation with increasing irradiation dose for HSQ (0–5mCcm−2) calculated from the ID/IG ratio of Raman peaks.

  2. Room-temperature measurements of non-local signal.
    Figure 2: Room-temperature measurements of non-local signal.

    aRNL versus n for pristine graphene and hydrogenated graphene at room temperature. The dark grey dashed lines show the ohmic contribution to the measured signal. Inset: ρ versus n for pristine and hydrogenated graphene. b, Dependence of the RNL on the percentage of hydrogenation. The dark grey dashed lines show the calculated ROhmic contribution for this sample.

  3. Magnetic field dependence of
RNL.
    Figure 3: Magnetic field dependence of RNL.

    Parallel-field precession data for the sample S2 with L/W=5 and mobility ~20,000cm2V−1s−1. A smooth background has been subtracted from the raw data (see Supplementary Information). The red dotted line is the fit for the experimental curves. The fitting gives λs~1.6μm.

  4. Length and width dependence of
RNL at room temperature.
    Figure 4: Length and width dependence of RNL at room temperature.

    a,b, At the CNP (a) and at n=1×1012cm−2 (b) for samples with 0.02% (red solid circles) and 0.05% (blue solid circles) hydrogenation. Here the length is the centre–centre distance between the injector and detector electrodes. The solid lines are the fit for the data and the dark grey dashed line is the calculated ohmic contribution at these charge carrier densities. c, RNL (red circles) as a function of width W (W=400nm–1.8μm) for a fixed length L (2μm). The solid red line is the fit for the data and the dark grey dashed line is the calculated ohmic contribution (inset: R versus W on a linear scale).

References

  1. Castro Neto, A. H. & Guinea, F. Impurity-induced spin–orbit coupling in graphene. Phys. Rev. Lett. 103, 026804 (2009).
  2. Kane, C. L. & Mele, E. J. Z(2) topological order and the quantum spin Hall effect. Phys. Rev. Lett. 95, 146802 (2005).
  3. Kane, C. L. & Mele, E. J. Quantum spin Hall effect in graphene. Phys. Rev. Lett. 95, 226801 (2005).
  4. Hirsch, J. E. Spin Hall effect. Phys. Rev. Lett. 83, 18341837 (1999).
  5. Schmidt, M. J. & Loss, D. Edge states and enhanced spin–orbit interaction at graphene/graphane interfaces. Phys. Rev. B 81, 165439 (2010).
  6. Conan, W., Jun, H., Jason, A., Marcel, F. & Ruqian, W. Engineering a robust quantum spin Hall state in graphene via adatom deposition. Phys. Rev. X 1, 021001 (2011).
  7. Zhou, J., Liang, Q. F. & Dong, J. M. Enhanced spin–orbit coupling in hydrogenated and fluorinated graphene. Carbon 48, 14051409 (2010).
  8. Rappoport, T. G., Uchoa, B. & Castro Neto, A. H. Magnetism and magnetotransport in disordered graphene. Phys. Rev. B 80, 245408 (2009).
  9. Seki, T. et al. Giant spin Hall effect in perpendicularly spin-polarized FePt/Au devices. Nature Mater. 7, 125129 (2008).
  10. Novoselov, K. S. et al. Electric field effect in atomically thin carbon films. Science 306, 666669 (2004).
  11. Lee, C., Wei, X. D., Kysar, J. W. & Hone, J. Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 321, 385388 (2008).
  12. Kim, E. A. & Castro Neto, A. H. Graphene as an electronic membrane. Europhys. Lett. 84, 57007 (2008).
  13. Loh, K. P., Bao, Q. L., Ang, P. K. & Yang, J. X. The chemistry of graphene. J. Mater. Chem. 20, 22772289 (2010).
  14. Elias, D. C. et al. Control of graphene’s properties by reversible hydrogenation: Evidence for graphane. Science 323, 610613 (2009).
  15. Nair, R. R. et al. Fluorographene: A two-dimensional counterpart of teflon. Small 6, 28772884 (2010).
  16. Fert, A. & Levy, P. M. Spin Hall effect induced by resonant scattering on impurities in metals. Phys. Rev. Lett. 106, 157208 (2011).
  17. Wunderlich, J., Kaestner, B., Sinova, J. & Jungwirth, T. Experimental observation of the spin-Hall effect in a two-dimensional spin–orbit coupled semiconductor system. Phys. Rev. Lett. 94, 047204 (2005).
  18. Kuemmeth, F., Ilani, S., Ralph, D. C. & McEuen, P. L. Coupling of spin and orbital motion of electrons in carbon nanotubes. Nature 452, 448452 (2008).
  19. Jespersen, T. S. et al. Gate-dependent spin–orbit coupling in multielectron carbon nanotubes. Nature Phys. 7, 348353 (2011).
  20. Kato, Y. K., Myers, R. C., Gossard, A. C. & Awschalom, D. D. Observation of spin Hall effect in semiconductors. Science 306, 19101913 (2004).
  21. Dyakonov, M. I. & Perel, V. I. Current-induced spin orientation of electrons in semiconductors. Phys. Lett. A 35, 459460 (1971).
  22. Valenzuela, S. O. & Tinkham, M. Direct electronic measurement of the spin Hall effect. Nature 442, 176179 (2006).
  23. Abanin, D. A. et al. Giant nonlocality near the Dirac point in graphene. Science 332, 328330 (2011).
  24. Brüne, C. et al. Spin polarization of the quantum spin Hall edge states. Nature Phys. 8, 485490 (2012).
  25. Ryu, S. et al. Reversible basal plane hydrogenation of graphene. Nano Lett. 8, 45974602 (2008).
  26. Jaiswal, M. et al. Controlled hydrogenation of graphene sheets and nanoribbons. ACS Nano 5, 888896 (2011).
  27. Cancado, L. G. et al. Quantifying defects in graphene via Raman spectroscopy at different excitation energies. Nano Lett. 11, 31903196 (2011).
  28. Hornekaer, L. et al. Clustering of chemisorbed H(D) atoms on the graphite (0001) surface due to preferential sticking. Phys. Rev. Lett. 97, 186102 (2006).
  29. Abanin, D. A., Shytov, A. V., Levitov, L. S. & Halperin, B. I. Nonlocal charge transport mediated by spin diffusion in the spin Hall effect regime. Phys. Rev. B 79, 035304 (2009).
  30. Mihajlovic, G., Pearson, J. E., Garcia, M. A., Bader, S. D. & Hoffmann, A. Negative nonlocal resistance in mesoscopic gold Hall bars: Absence of the giant spin Hall effect. Phys. Rev. Lett. 103, 166601 (2009).
  31. Tombros, N. et al. Electronic spin transport and spin precession in single graphene layers at room temperature. Nature 448, 571574 (2007).
  32. Yang, T-Y. et al. Observation of long spin-relaxation times in bilayer graphene at room temperature. Phys. Rev. Lett. 107, 047206 (2011).
  33. Avsar, A. et al. Toward wafer scale fabrication of graphene based spin valve devices. Nano Lett. 11, 23632368 (2011).
  34. Patra, A. K. et al. Dynamic spin injection into chemical vapor deposited graphene. Appl. Phys. Lett. 101, 162407 (2012).
  35. McCreary, K. M., Swartz, A. G., Han, W., Fabian, J. & Kawakami, R. K. Magnetic moment formation in graphene detected by scattering of pure spin currents. Phys. Rev. Lett. 109, 186604 (2012).
  36. Kettemann, S. Dimensional control of antilocalization and spin relaxation in quantum wires. Phys. Rev. Lett. 98, 176808 (2007).
  37. Paul, W. & Stefan, K. in Handbook of Nanophysics: Nanotubes and Nanowires Ch 28 (CRC Press, 2010).
  38. Huertas-Hernando, D., Guinea, F. & Brataas, A. Spin–orbit-mediated spin relaxation in graphene. Phys. Rev. Lett. 103, 146801 (2009).
  39. Ochoa, H., Castro Neto, A. H. & Guinea, F. Elliot–Yafet mechanism in graphene. Phys. Rev. Lett. 108, 206808 (2012).
  40. Konschuh, S., Gmitra, M. & Fabian, J. Tight-binding theory of the spin–orbit coupling in graphene. Phys. Rev. B 82, 245412 (2010).
  41. Duplock, E. J., Scheffler, M. & Lindan, P. J. D. Hallmark of perfect graphene. Phys. Rev. Lett. 92, 225502 (2004).
  42. Maekawa, S. (ed.) in Concepts in Spin Electronics Ch. 8, 363367 (Oxford Univ. Press, 2006).

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Author information

  1. These authors contributed equally to this work

    • Jayakumar Balakrishnan &
    • Gavin Kok Wai Koon

Affiliations

  1. Department of Physics, 2 Science Drive 3, National University of Singapore, Singapore 117542, Singapore

    • Jayakumar Balakrishnan,
    • Gavin Kok Wai Koon,
    • Manu Jaiswal,
    • A. H. Castro Neto &
    • Barbaros Özyilmaz
  2. Graphene Research Centre, 6 Science Drive 2, National University of Singapore, Singapore 117546, Singapore

    • Jayakumar Balakrishnan,
    • Gavin Kok Wai Koon,
    • Manu Jaiswal,
    • A. H. Castro Neto &
    • Barbaros Özyilmaz
  3. Nanocore, 4 Engineering Drive 3, National University of Singapore, Singapore 117576, Singapore

    • Gavin Kok Wai Koon &
    • Barbaros Özyilmaz
  4. NUS Graduate School for Integrative Sciences and Engineering (NGS), Centre for Life Sciences (CeLS), 28 Medical Drive, Singapore 117456, Singapore

    • A. H. Castro Neto &
    • Barbaros Özyilmaz
  5. Present address: Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India

    • Manu Jaiswal

Contributions

B.Ö. devised and supervised the project. J.B. and B.Ö. designed the experiments. J.B. and G.K.W.K. performed the experiments. A.H.C.N. provided the theoretical work. All authors carried out the data analysis and discussed the results. J.B., A.H.C.N. and B.Ö. co-wrote the paper.

Competing financial interests

The authors declare no competing financial interests.

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