Felix Passmann

Dynamical Formation and Manipulation of the Persistent Spin Helix

Understanding and manipulation of electron spin dynamics and transport in low-dimensional semiconductor nanostructures is a key requirement for functional quantum technologies. In this work, a time- and space-resolved magneto-optic Kerr microscope is employed to explore the effect of momentum-dependent effective magnetic fields on the spin dynamics of a two-dimensional electron gas in high-mobility GaAs and CdTe quantum wells. Both structures feature nearly equal Dresselhaus and Rashba spin orbit coupling, enabling the emergence of a unidirectional spin wave texture with SU(2) symmetry, the so-called persistent spin helix. The spin orbit coupling can be quantified directly from the experimentally extracted coherent spin precession pattern. It is observed that application of (i) perpendicular in-plane magnetic fields allows for the extraction of the spin orbit coupling parameters. (ii) Out-of-plane gate fields tune the Rashba and cubic Dresselhaus parameter directly and (iii) in-plane electric fields vary the modulation frequency of the spin helix and the diffusion coefficient. In the CdTe sample reveals a fine tuning of the pattern via (iv) optical doping, creating a local gradient of the spin orbit coupling parameters. Precise engineering of all spin control mechanisms enables a regime of locked spin transport where effective magnetic fields are suppressed.  All experimental results are supported by qualitative kinetic theory and Monte Carlo simulations.