Far out-of-equilibrium spin populations trigger giant spin injection into atomically thin MoS2

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Abstract

Injecting spins from ferromagnetic metals into semiconductors efficiently is a crucial step towards the seamless integration of charge- and spin-information processing in a single device1,2. However, efficient spin injection into semiconductors has remained an elusive challenge even after almost three decades of major scientific effort3,4,5, due to, for example, the extremely low injection efficiencies originating from impedance mismatch1,2,5,6, or technological challenges originating from stability and the costs of the approaches7,8,9,10,11,12. We show here that, by utilizing the strongly out-of-equilibrium nature of subpicosecond spin-current pulses, we can obtain a massive spin transfer even across a bare ferromagnet/semiconductor interface. We demonstrate this by producing ultrashort spin-polarized current pulses in Co and injecting them into monolayer MoS2, a two-dimensional semiconductor. The MoS2 layer acts both as the receiver of the spin injection and as a selective converter of the spin current into a charge current, whose terahertz emission is then measured. Strikingly, we measure a giant spin current, orders of magnitude larger than typical injected spin-current densities using currently available techniques. Our result demonstrates that technologically relevant spin currents do not require the very strong excitations typically associated with femtosecond lasers. Rather, they can be driven by ultralow-intensity laser pulses, finally enabling ultrashort spin-current pulses to be a technologically viable information carrier for terahertz spintronics.

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Fig. 1: Ultrafast spin-injection process.
Fig. 2: Characterization of MoS2 and Co/MoS2 samples.
Fig. 3: THz emission of Co/MoS2 under different experimental conditions.
Fig. 4: Strongly out-of-equilibrium distribution of spin injection.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

References

  1. 1.

    Bercioux, D. & Lucignano, P. Quantum transport in Rashba spin–orbit materials: a review. Rep. Prog. Phys. 78, 106001 (2015).

  2. 2.

    Tang, J. & Wang, K. L. Electrical spin injection and transport in semiconductor nanowires: challenges, progress and perspectives. Nanoscale 7, 4325–4337 (2015).

  3. 3.

    Sinova, J., Valenzuela, S. O., Wunderlich, J., Back, C. H. & Jungwirth, T. Spin Hall effects. Rev. Mod. Phys. 87, 1213–1259 (2015).

  4. 4.

    Awschalom, D. D. & Flatte, M. E. Challenges for semiconductor spintronics. Nat. Phys. 3, 153–159 (2007).

  5. 5.

    Schmidt, G., Ferrand, D., Molenkamp, L. W., Filip, A. T. & van Wees, B. J. Fundamental obstacle for electrical spin injection from a ferromagnetic metal into a diffusive semiconductor. Phys. Rev. B 62, R4790 (2000).

  6. 6.

    Jansen, R. Silicon spintronics. Nat. Mater. 11, 400–408 (2012).

  7. 7.

    Appelbaum, I., Huang, B. Q. & Monsma, D. J. Electronic measurement and control of spin transport in silicon. Nature 447, 295–298 (2007).

  8. 8.

    Jonker, B. T., Kioseoglou, G., Hanbicki, A. T., Li, C. H. & Thompson, P. E. Electrical spin-injection into silicon from a ferromagnetic metal/tunnel barrier contact. Nat. Phys. 3, 542–546 (2007).

  9. 9.

    Debray, P. et al. All-electric quantum point contact spin-polarizer. Nat. Nanotechnol. 4, 759–764 (2009).

  10. 10.

    Chuang, P. et al. All-electric all-semiconductor spin field-effect transistors. Nat. Nanotechnol. 10, 35–39 (2015).

  11. 11.

    Wunderlich, J. et al. Spin-injection Hall effect in a planar photovoltaic cell. Nat. Phys. 5, 675–681 (2009).

  12. 12.

    Wunderlich, J. et al. Spin Hall effect transistor. Science 330, 1801–1804 (2010).

  13. 13.

    Battiato, M., Carva, K. & Oppeneer, P. M. Superdiffusive spin transport as a mechanism of ultrafast demagnetization. Phys. Rev. Lett. 105, 027203 (2010).

  14. 14.

    Kampfrath, T. et al. Terahertz spin current pulses controlled by magnetic heterostructures. Nat. Nanotechnol. 8, 256–260 (2013).

  15. 15.

    Seifert, T. et al. Efficient metallic spintronic emitters of ultrabroadband terahertz radiation. Nat. Photon. 10, 483–488 (2016).

  16. 16.

    Yang, D. et al. Powerful and tunable THz emitters based on the Fe/Pt magnetic heterostructure. Adv. Opt. Mater. 4, 1944–1949 (2016).

  17. 17.

    Wu, Y. et al. High-performance THz emitters based on ferromagnetic/nonmagnetic heterostructures. Adv. Mater. 29, 1603031 (2017).

  18. 18.

    Eschenlohr, A. et al. Ultrafast spin transport as key to femtosecond demagnetization. Nat. Mater. 12, 332–336 (2013).

  19. 19.

    Rudolf, D. et al. Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current. Nat. Commun. 3, 1037 (2012).

  20. 20.

    Battiato, M. & Held, K. Ultrafast and gigantic spin injection in semiconductors. Phys. Rev. Lett. 116, 196601 (2016).

  21. 21.

    Zhukov, V., Chulkov, E. & Echenique, P. Lifetimes and inelastic mean free path of low-energy excited electrons in Fe, Ni, Pt, and Au: Ab initio GW+T calculations. Phys. Rev. B 73, 125105 (2006).

  22. 22.

    Shao, Q. et al. Strong Rashba–Edelstein effect-induced spin–orbit torques in monolayer transition metal dichalcogenide/ferromagnet bilayers. Nano Lett. 16, 7514–7520 (2016).

  23. 23.

    Tao, J. et al. Growth of wafer-scale MoS2 monolayer by magnetron sputtering. Nanoscale 7, 2497–2503 (2015).

  24. 24.

    Huisman, T. J. et al. Femtosecond control of electric currents in metallic ferromagnetic heterostructures. Nat. Nanotechnol. 11, 455–458 (2016).

  25. 25.

    Shen, J. et al. Damping modulated terahertz emission of ferromagnetic films excited by ultrafast laser pulses. Appl. Phys. Lett. 101, 072401 (2012).

  26. 26.

    Huisman, T. J., Mikhaylovskiy, R. V., Tsukamoto, A., Rasing, T. & Kimel, A. V. Simultaneous measurements of terahertz emission and magneto-optical Kerr effect for resolving ultrafast laser-induced demagnetization dynamics. Phys. Rev. B 92, 104419 (2015).

  27. 27.

    Huang, Y. et al. Surface optical rectification from layered MoS2 crystal by THz time-domain surface emission spectroscopy. ACS Appl. Mater. Interfaces 9, 4956–4965 (2017).

  28. 28.

    Braun, L. et al. Ultrafast photocurrents at the surface of the three-dimensional topological insulator Bi2Se3. Nat. Commun. 7, 13259 (2016).

  29. 29.

    Laman, N., Bieler, M. & van Drielb, H. M. Ultrafast shift and injection currents observed in wurtzite semiconductors via emitted terahertz radiation. J. Appl. Phys. 98, 103507 (2005).

  30. 30.

    Choi, G.-M., Min, B.-C., Lee, K.-J. & Cahill, D. G. Spin current generated by thermally driven ultrafast demagnetization. Nat. Commun. 5, 4334 (2014).

  31. 31.

    Choi, G.-M., Moon, C.-H., Min, B.-C., Lee, K.-J. & Cahill, D. G. Thermal spin-transfer torque driven by the spin-dependent Seebeck effect in metallic spin-valves. Nat. Phys. 11, 576–581 (2015).

  32. 32.

    Mak, K. F., Lee, C., Hone, J., Shan, J. & Heinz, T. F. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).

  33. 33.

    Rojas Sanchez, J. C. et al. Spin-to-charge conversion using Rashba coupling at the interface between non-magnetic materials. Nat. Commun. 4, 2944 (2013).

  34. 34.

    Ando, K. et al. Electrically tunable spin injector free from the impedance mismatch problem. Nat. Mater. 10, 655–659 (2011).

  35. 35.

    Dash, S. P., Sharma, S., Patel, R. S., de Jong, M. P. & Jansen, R. Electrical creation of spin polarization in silicon at room temperature. Nature 462, 491–494 (2009).

  36. 36.

    La-o-vorakiat, C. et al. Elucidating the role of disorder and free-carrier recombination kinetics in CH3NH3PbI3 perovskite films. Nat. Commun. 6, 7903 (2015).

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Acknowledgements

We acknowledge funding from the A*STAR PHAROS Programme on Topological Insulators (SERC Grant No. 152 74 00026) and 2D Materials (SERC Grant No. 152 70 00012 and 152 70 00016), and Singapore Ministry of Education AcRF Tier 1 (MOE2018-T1-001-97) and Tier 2 (MOE2015-T2-2-065, MOE2016-T2-1-054) grants. J.C.W.S. acknowledges the support of the Singapore National Research Foundation under fellowship award NRF-NRFF2016-05. M.B. gratefully acknowledges Nanyang Technological University, NAP-SUG and the Austrian Science Fund (FWF) through Lise Meitner position M1925-N28 for the funding of this research. The work was supported in part by the Center for Integrated Nanotechnologies, a US DOE BES user facility. We acknowledge B. Tang from the National University of Singapore and D. Seng from the Institute of Materials Research and Engineering, A*STAR, for Raman and X-ray photoelectron spectroscopy data.

Author information

E.E.M.C. and H.Y. conceived the experiments. W.Y., Y.W. and M.C. fabricated the heterostructures. L.C. and X.W. carried out the THz measurements and data analysis with the help and guidance of E.E.M.C. and H.Y. M.B., J.C.W.S. and J.X.Z. provided theoretical inputs. W.Y. and S.W. performed and analysed the X-ray photoelectron spectroscopy and Raman measurements. L.C., X.W., J.C.W.S, M.B. and E.E.M.C wrote the manuscript together. All authors discussed the results and commented on the manuscript.

Correspondence to Justin C. W. Song or Marco Battiato or Hyunsoo Yang or Elbert E. M. Chia.

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Supplementary Information

Supplementary Chapters 1–8, Supplementary Figures 1–7 and Supplementary References 1–12

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Cheng, L., Wang, X., Yang, W. et al. Far out-of-equilibrium spin populations trigger giant spin injection into atomically thin MoS2. Nat. Phys. 15, 347–351 (2019) doi:10.1038/s41567-018-0406-3

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