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Spin–valley phase diagram of the two-dimensional metal–insulator transition

Nature Physics volume 3, pages 388391 (2007) | Download Citation

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Abstract

The metallic behaviour of the resistivity observed at low temperatures in low-disorder, dilute, two-dimensional (2D) carrier systems is of considerable interest as it defies the scaling theory of localization in two dimensions1. Although the origin of the metallic behaviour remains unknown and controversial, there is widespread evidence that the spin degree of the freedom plays a crucial role. Here, we directly probe the role of another discrete electronic degree of freedom, namely the valley polarization. Using symmetry-breaking strain together with an in-plane magnetic field to tune the valley and spin polarizations of an AlAs 2D electron system at fixed density, we map out a spin–valley phase diagram for its metal–insulator transition. The insulating phase occurs in the quadrant where the system is sufficiently spin and valley polarized. This observation establishes the equivalent roles of spin and valley degrees of freedom in the 2D metal–insulator transition.

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Acknowledgements

We thank the NSF and ARO for support and Y. P. Shkolnikov, E. Tutuc and K. Lai for illuminating discussions.

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Affiliations

  1. Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA

    • O. Gunawan
    • , T. Gokmen
    • , K. Vakili
    • , M. Padmanabhan
    • , E. P. De Poortere
    •  & M. Shayegan

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The authors declare no competing financial interests.

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Correspondence to M. Shayegan.

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DOI

https://doi.org/10.1038/nphys596

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