Markus Betz
Experimentelle Physik 2, TU Dortmund

Dynamical formation and manipulation of persistent spin helices
in two-dimensional electron gases

The spin-orbit interaction in two-dimensional electron gases is responsible for a broad range of phenomena,
including spin Hall effects and spin textures such as the persistent spin helix (PSH). A PSH occurs when
parameters associated with the bulk (Dresselhaus) and structural (Rashba) inversion asymmetries are roughly
equal in strength. This situation results in a momentum-dependent effective magnetic field providing the SU(2)
symmetry in which the two-dimensional electron gas (2DEG) features a unidirectional spin grating (or helical
spin-density wave). Here I will focus on several new aspects of PSH formation and manipulation obtained from
temporally and spatially resolved Kerr microscopy. In a first set of experiment we find a marked influence of
weak in-plane electric fields on the effective spin-orbit coupling in a high-mobility GaAs 2DEG. In addition we
explore the regime of a “traveling” persistent spin helix. Here, the combined influence of weak electric and
moderate magnetic fields moves the electron ensemble while the spin orientation at a given position remains
constant. We then move on to investigate the emergence of a PSH in CdTe quantum wells. Here we find a
marked influence of optical doping on the resulting spin texture. Most findings agree well with simulations of
the spin texture based on kinetic theory.