Doppler velocimetry of spin and charge currents in the 2D Fermi gas

Abstract

Abstract. Phase-sensitive transient grating spectroscopy was used to measure the Doppler shift of light diffracted off moving spin and charge density waves, allowing complete characterization of spin and charge transport in the 2D Fermi gas. Summary of resultsWe used phase-sensitive transient grating spectroscopy [1] to measure spin and charge transport in a 2D electron gas residing in a GaAs quantum well. We found that spin transport takes the form of helical motion in the presence of linear spin-orbit coupling, and that spin symmetry can be restored in the form of a persistent spin helix [2] with proper tuning of the quantum well growth parameters. Our optical transport measurements show that in a current carrying electron gas, spins and electronhole pairs are not directly affected by an applied electric field, but rather are pushed along by the force exerted on them by the drifting Fermi sea. Spin diffusion is reduced relative to charge diffusion by electron-electron interactions [3], while the spin mobility is precisely equal to the electron mobility, leading to an anomalous rigidity of spin packets [4] (See Fig. 1). While spin drifts at the velocity of the Fermi sea, electron-hole pairs drift at the much lower ambipolar velocity because of the large hole mass [5]. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.