Emergence of the persistent spin helix in semiconductor quantum wells

Authors

J. D. Koralek
Christopher P. Weber, Santa Clara UniversityFollow
J. Orenstein
B. Andrei Bernevig
Shou-Cheng Zhang
S. Mack
D. D. Awschalom

Document Type

Article

Publication Date

4-1-2009

Publisher

Springer

Abstract

According to Noether’s theorem¹, 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 electron’s 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 coupling². The corresponding conserved quantities include the amplitude and phase of a helical spin density wave termed the ‘persistent spin helix’². SU(2) is realized, in principle, when the strengths of two dominant spin–orbit interactions, the Rashba³ (strength parameterized by α) and linear Dresselhaus⁴ (β₁) interactions, 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 (β₃) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as α approaches β₁. Here we report experimental observation of the emergence of the persistent spin helix in GaAs quantum wells by independently tuning α and β₁. Using transient spin-grating spectroscopy⁵, we find a spin-lifetime enhancement of two orders of magnitude near the symmetry point. Excellent quantitative agreement with theory across a wide range of sample parameters allows us to obtain an absolute measure of all relevant spin–orbit terms, identifying β₃ as the main SU(2)-violating term in our samples. The tunable suppression of spin relaxation demonstrated in this work is well suited for application to spintronics^6,7.

Comments

The final publication is available at Springer via https://doi.org/10.1038/nature07871

Recommended Citation

Koralek, J. D., Weber, C. P., Orenstein, J., Bernevig, B. A., Zhang, S.-C., Mack, S., & Awschalom, D. D. (2009). Emergence of the persistent spin helix in semiconductor quantum wells. Nature, 458(7238), 610–613. https://doi.org/10.1038/nature07871