Magneto-Raman spectroscopy of spin-density excitations in (001)-grown GaAs-AlGaAs quantum wells in the regime of the persistent spin helix

We present inelastic light scattering experiments on low-energy intrasubband spin-density excitations (SDE) in 12-nm-wide (001)-oriented GaAs-AlGaAs single quantum well samples with balanced Rashba and Dresselhaus spin-orbit interaction strengths. This unique symmetry causes an effective spin-orbit field either parallel or antiparallel to specific in-plane crystal directions, which supports the persistent spin helix. This results in a highly anisotropic splitting of intrasubband SDEs in the conduction band. Measurements are performed in backscattering geometry, where the SDE is formed by spin-flip intrasubband transitions. A wave-vector transfer into the two-dimensional electron system is realized by tilting the sample. By rotating the sample with a rotary stage, we can precisely map the anisotropic spin splitting, which appears for various crystal directions as a double peak line shape of the spectra. In the presence of external magnetic fields, a superposition of both, the intrinsic spin-orbit field and the external magnetic field, occurs. We analyze our experimental spectra via a lineshape analysis, based on the Lindhard-Mermin lineshape, including the effects of the anisotropic spin splitting and the external magnetic field. This allows us to quantitatively deduce the spin-orbit parameters, the electron g factor, and the single-particle relaxation time from our observations.

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