Spin Helices in GaAs Quantum Wells and Quantum Wires
This talk will cover two topics. First I will present evidence for helical nuclear spin order in GaAs cleaved edge overgrowth wires. The conductance of the first mode is reduced from 2 e2/h down to 1 e2/h upon lowering temperature from 10 K to below 0.1 K, suggesting lifting of the electron spin
degeneracy in the absence of B. Our results are consistent with theoretical predictions for helical nuclear magnetism in the Luttinger liquid regime.
Second: The spin-orbit (SO) interaction is a crucial resource for spin-based quantum technologies, but also causes spin decay by dephasing and relaxation. In semiconductors, it is possible to protect spins from decay by matching the Rashba and Dresselhaus fields, creating the persistent spin helix state. We report locking of the Rashba and Dresselhaus SO fields to matching strengths while changing both together in this locked state with top and back gates, providing a technique to manipulate spins while keeping them protected from decay. We employ the suppression of weak antilocalization as sensitive detector for matched SO fields, delivering all SO terms when combined with numerical simulations. These techniques are applicable to various semiconductor materials and nanostructures.