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Title: Emergence of the persistent spin helix in semiconductor quantum wells

Abstract

According to Noether’s 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 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. Yet, 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 strengths of two dominant spin–orbit interactions, the Rashba (strength parameterized by α) and linear Dresselhaus (β 1) 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 (β 3) and spin-dependent scattering. When these terms are negligible, the distance over which spin information can propagate is predicted to diverge as α approaches β 1. Here we introduce experimental observation of themore » emergence of the persistent spin helix in GaAs quantum wells by independently tuning α and β 1. Using transient spin-grating spectroscopy, 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 β 3 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.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [6]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Santa Clara Univ., Santa Clara, CA (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
  4. Princeton Univ., NJ (United States)
  5. Stanford Univ., CA (United States)
  6. Univ. of California, Santa Barbara, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; National Science Foundation (NSF); US Department of the Navy, Office of Naval Research (ONR)
OSTI Identifier:
1443050
Report Number(s):
SLAC-PUB-13988
Journal ID: ISSN 0028-0836
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
Nature (London)
Additional Journal Information:
Journal Name: Nature (London); Journal Volume: 458; Journal Issue: 7238; Journal ID: ISSN 0028-0836
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS

Citation Formats

Koralek, J. D., Weber, C. P., Orenstein, J., Bernevig, B. A., Zhang, Shou-Cheng, Mack, S., and Awschalom, D. D. Emergence of the persistent spin helix in semiconductor quantum wells. United States: N. p., 2009. Web. doi:10.1038/nature07871.
Koralek, J. D., Weber, C. P., Orenstein, J., Bernevig, B. A., Zhang, Shou-Cheng, Mack, S., & Awschalom, D. D. Emergence of the persistent spin helix in semiconductor quantum wells. United States. doi:10.1038/nature07871.
Koralek, J. D., Weber, C. P., Orenstein, J., Bernevig, B. A., Zhang, Shou-Cheng, Mack, S., and Awschalom, D. D. Thu . "Emergence of the persistent spin helix in semiconductor quantum wells". United States. doi:10.1038/nature07871. https://www.osti.gov/servlets/purl/1443050.
@article{osti_1443050,
title = {Emergence of the persistent spin helix in semiconductor quantum wells},
author = {Koralek, J. D. and Weber, C. P. and Orenstein, J. and Bernevig, B. A. and Zhang, Shou-Cheng and Mack, S. and Awschalom, D. D.},
abstractNote = {According to Noether’s 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 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. Yet, 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 strengths of two dominant spin–orbit interactions, the Rashba (strength parameterized by α) and linear Dresselhaus (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 introduce experimental observation of the emergence of the persistent spin helix in GaAs quantum wells by independently tuning α and β1. Using transient spin-grating spectroscopy, 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.},
doi = {10.1038/nature07871},
journal = {Nature (London)},
number = 7238,
volume = 458,
place = {United States},
year = {2009},
month = {4}
}

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