Direct determination of spin-orbit interaction coefficients and realization of the persistent spin helix symmetry
Nature Nanotechnology  (2014), doi:10.1038/nnano.2014.128

A. Sasaki, S. Nonaka, Y. Kunihashi, M. Kohda, T. Bauernfeind, T. Dollinger, K. Richter und J. Nitta

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The spin–orbit interaction plays a crucial role in diverse fields of condensed matter. In III–V zinc-blende semiconductor heterostructures, two types of spin–orbit interaction—Rashba and Dresselhaus—act on the electron spin as effective magnetic fields. They are characterized by coefficients α and β, respectively. When α is equal to β, the so-called persistent spin helix symmetry is realized. In this condition, invariance with respect to spin rotations is achieved even in the presence of the spin–orbit interaction, implying strongly enhanced spin lifetimes for spatially periodic spin modes. Existing methods to evaluate α/β require fitting analyses that often include ambiguity in the parameters used.
In a recent publication of Klaus Richter's theory group with experimental physicists from Tohoku University in Sendai (Japan), a simple all-electrical and fitting parameter-free technique has been demonstrated to determine α/β and to deduce the absolute values of α and β. The method is based on the detection of the effective magnetic field direction and the strength induced by the two spin–orbit interactions. Moreover,  the persistent spin helix symmetry has been demonstrated by gate tuning.

Electron microscope images of the wire structures (left) and schematic illustration of measurement configuration

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