130712 dorothee socgraphene

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    Colossal enhancement of spin orbit couplingin weakly hydrogenated graphene

    J. Balakrishnan, G. K. W. Koon, M. Jaiswal, A. H. Castro Neto, B. zilmazNature 9, 284 (2013)

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    Outline Spin orbit in graphene

    Spin Hall effect and measurement

    Fabrication of the samples

    Measurements at RT and 4K

    Conclusion

    12.07.2013 2

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    Spin orbit coupling in graphene

    12.07.2013 Konschuh, PRB 82 245412 (2010); J. Balakrishnan, DOI:10.1038/NPHYS2576 3

    Curved graphene:

    SpinAtomic spin orbit strength, l=s,p,d..SO gapStates at K/K pointStates at A/B point

    Energy of orbital

    V Hopping parameter

    with

    Flat graphene:

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    Spin Hall effect

    12.07.2013 J. E. Hirsch, PRL 83, 9 (1999); J. Balakrishnan, DOI:10.1038/NPHYS2576 4

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    Sample fabrication Graphene exfoliation

    EBL for contacts

    EBL for Hall bar

    Coating of sample with HSQ

    EBL exposure of HSQ

    12.07.2013 J. Balakrishnan, G. K. W. Koon, M. Jaiswal, A. H. Castro Neto, B. zyilmaz, DOI:10.1038/NPHYS2576 5

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    Calculation of impurity concentration

    12.07.2013 J. Balakrishnan, G. K. W. Koon, M. Jaiswal, A. H. Castro Neto, B. zyilmaz, DOI:10.1038/NPHYS2576 6

    Hydrogenation =

    Dose ~

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    RNL, Rohmic and measurements

    12.07.2013 J. Balakrishnan, G. K. W. Koon, M. Jaiswal, A. H. Castro Neto, B. zyilmaz, DOI:10.1038/NPHYS2576 7

    W Width of sampleL Length of sample Resistivity

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    In-plane magnetic field dependence T=4 K

    12.07.2013 J. Balakrishnan, G. K. W. Koon, M. Jaiswal, A. H. Castro Neto, B. zyilmaz, DOI:10.1038/NPHYS2576 8

    Sample hydrogentation: 0.01%

    Gyromagnetic ratio

    Spin diffusion constantSpin precession lengthWidth of sampleLength of sampleSpin Hall coefficentSpin dephasing time

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    Width and length dependence of RNL, RT

    12.07.2013 J. Balakrishnan, G. K. W. Koon, M. Jaiswal, A. H. Castro Neto, B. zyilmaz, DOI:10.1038/NPHYS2576 9

    =1 m

    H = 0.02%, =1600cm2/(VS)H = 0.05%, =900cm2/(VS)

    H = 0.01%, =1400cm2/(VS)

    ~

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    Determination of s and SO

    12.07.2013 J. Balakrishnan, DOI:10.1038/NPHYS2576: 10

    Elliott-Yafet scattering

    At adatom (H), out of plane bending: and orbital mixing!

    SO becomes first order effect

    Fermi energy

    Momentum relaxation timeSO coupling strength

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    Conclusion Increase of SOE by partial hydrogenation of graphene

    Measurement of SHE in graphene using SOE

    Oscilation of RNL in dependence of BII

    Clear dependence of RNL with the sample width andlength

    12.07.2013 11

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    Dresselhaus and Rashba terms

    12.07.2013 12J. Balakrishnan, DOI:10.1038/NPHYS2576:

    Starting Hamiltonian:

    Dresselhaus term:

    Rashba term: