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arXiv · 0903.4709

Emergence of the persistent spin helix in semiconductor quantum wells

Jake D. Koralek·Chris Weber·Joe Orenstein·Andrei Bernevig·Shou-Cheng Zhang·Shawn Mack·David Awschalom
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Abstract

According to Noethers theorem, for every symmetry in nature there is a corresponding conservation law. For example, invariance with respect to spatial translation corresponds to conservation of momentum. In another well-known example, invariance with respect to rotation of the electrons spin, or SU(2) symmetry, leads to conservation of spin polarization. For electrons in a solid, this symmetry is ordinarily broken by spin-orbit coupling, allowing spin angular momentum to flow to orbital angular momentum. However, it has recently been predicted that SU(2) can be achieved in a two-dimensional electron gas, despite the presence of spin-orbit coupling. The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the persistent spin helix. SU(2) is realized, in principle, when the strength of two dominant spin-orbit interactions, the Rashba (strength parameterized by α) and linear Dresselhaus (β_1), are equal. This symmetry is predicted to be robust against all forms of spin-independent scattering, including electron-electron interactions, but is broken by the cubic Dresselhaus term (β_3) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as αapproaches β_1. Here we observe experimentally the emergence of the persistent spin helix in GaAs quantum wells by independently tuning αand β_1. Using transient spin-grating spectroscopy, we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point.........

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Jake D. Koralek, Chris Weber, Joe Orenstein, Andrei Bernevig, Shou-Cheng Zhang, Shawn Mack, David Awschalom. 2009-03-28. Emergence of the persistent spin helix in semiconductor quantum wells. https://doi.org/10.1038/nature07871

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