11 research outputs found
Direct determination of spin orbit interaction coefficients and realization of the persistent spin helix symmetry
The spin orbit interaction plays a crucial role in diverse fields of
condensed matter, including the investigation of Majorana fermions, topological
insulators, quantum information and spintronics. 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 with
different directions. They are characterized by coefficients alpha and beta,
respectively. When alpha is equal to beta, 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 alpha/beta require fitting analyses that often
include ambiguity in the parameters used. Here, we experimentally demonstrate a
simple and fitting parameter free technique to determine alpha/beta and to
deduce the absolute values of alpha and beta. The method is based on the
detection of the effective magnetic field direction and the strength induced by
the two spin orbit interactions. Moreover, we observe the persistent spin helix
symmetry by gate tuning.Comment: 34 pages with 7 figures including supplementary information. appears
in Nature Nanotechnology (2014) Published online 13 July 201
Spin relaxation: From 2D to 1D
In inversion asymmetric semiconductors, spin-orbit interactions give rise to
very effective relaxation mechanisms of the electron spin. Recent work, based
on the dimensionally constrained D'yakonov Perel' mechanism, describes
increasing electron-spin relaxation times for two-dimensional conducting layers
with decreasing channel width. The slow-down of the spin relaxation can be
understood as a precursor of the one-dimensional limit
Gate-controlled persistent spin helix state in (In,Ga)As quantum wells
In layered semiconductors with spin-orbit interaction (SOI) a persistent spin helix (PSH) state with suppressed spin relaxation is expected if the strengths of the Rashba and Dresselhaus SOI terms, α and β, are equal. Here we demonstrate gate control and detection of the PSH in two-dimensional electron systems with strong SOI including terms cubic in momentum. We consider strain-free InGaAs/InAlAs quantum wells and first determine a ratio α/β≃1 for nongated structures by measuring the spin-galvanic and circular photogalvanic effects. Upon gate tuning the Rashba SOI strength in a complementary magnetotransport experiment, we monitor the complete crossover from weak antilocalization via weak localization to weak antilocalization, where the emergence of weak localization reflects a PSH-type state. A corresponding numerical analysis reveals that such a PSH-type state indeed prevails even in presence of strong cubic SOI, however no longer at α=β