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Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry

Nature Nanotechnology volume 9, pages 611617 (2014) | Download Citation

Abstract

The valley degree of freedom of electrons is attracting growing interest as a carrier of information in various materials, including graphene, diamond and monolayer transition-metal dichalcogenides. The monolayer transition-metal dichalcogenides are semiconducting and are unique due to the coupling between the spin and valley degrees of freedom originating from the relativistic spin–orbit interaction. Here, we report the direct observation of valley-dependent out-of-plane spin polarization in an archetypal transition-metal dichalcogenide—MoS2—using spin- and angle-resolved photoemission spectroscopy. The result is in fair agreement with a first-principles theoretical prediction. This was made possible by choosing a 3R polytype crystal, which has a non-centrosymmetric structure, rather than the conventional centrosymmetric 2H form. We also confirm robust valley polarization in the 3R form by means of circularly polarized photoluminescence spectroscopy. Non-centrosymmetric transition-metal dichalcogenide crystals may provide a firm basis for the development of magnetic and electric manipulation of spin/valley degrees of freedom.

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Acknowledgements

The authors thank J. T. Ye, Y. Kasahara, J. Fujioka, S. Z. Bisri and Y. Kaneko for help with sample preparation and characterization, T. Shimojima, K. Shirai and K. Sumida for help with SARPES measurements, S. Shin, A. Kimura, H. Namatame and M. Taniguchi for sharing SARPES infrastructure, and Y. Nomura for useful comments on bandstructure calculations. The authors also thank T. Banno for his help with the maintenance of the photoluminescence measurement system. R.S. is supported by the Leading Graduate Program of Materials Education for future leaders in Research, Industry and Technology (MERIT). M.S. and Y.J.Z. are supported by the Advanced Leading Graduate Course for Photon Science (ALPS) and by a research fellowship for young scientists from JSPS. This research was partly supported by the Strategic International Collaborative Research Program (SICORP-LEMSUPER) and Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Research Hub for Advanced Nano Characterization, The University of Tokyo, supported by MEXT, Japan, as well as by a Grant-in-Aid for Scientific Specially Promoted Research (nos. 25000003 and 23244066) and the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program) from JSPS, Japan.

Author information

Author notes

    • R. Suzuki
    •  & M. Sakano

    These authors contributed equally to this work

Affiliations

  1. Quantum-Phase Electronics Centre (QPEC) and Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan

    • R. Suzuki
    • , M. Sakano
    • , Y. J. Zhang
    • , R. Akashi
    • , K. Ishizaka
    • , R. Arita
    •  & Y. Iwasa
  2. RIKEN Centre for Emergent Matter Science, Wako 351-0198, Japan

    • D. Morikawa
    • , R. Arita
    •  & Y. Iwasa
  3. Institute for Solid State Physics, University of Tokyo, Kashiwa, 277-8581, Japan

    • A. Harasawa
    •  & K. Yaji
  4. Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan

    • K. Kuroda
  5. Hiroshima Synchrotron Radiation Centre, Hiroshima University, Higashi-Hiroshima 739-0046, Japan

    • K. Miyamoto
    •  & T. Okuda

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Contributions

R.S., Y.Z. and Y.I. conceived and designed the research. R.S. grew and characterized all the crystals used in the research and D.M. generated CBED patterns. M.S., K.I., A.H., K.Y., K.K., K.M. and T.O. performed SARPES measurements. M.S. and K.I. analysed (S)ARPES data. First-principles calculations were made by R.Ak. and R.Ar. Y.Z. built a photoluminescence measurement system and R.S. measured the photoluminescence spectra. R.S., M.S., Y.Z., R.Ak., D.M., K.I., R.Ar. and Y.I. wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to K. Ishizaka or Y. Iwasa.

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DOI

https://doi.org/10.1038/nnano.2014.148

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