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Register a new userSpin Susceptibility of a 2D Electron System in GaAs towards the Weak Interaction Region
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We determine the spin susceptibility $chi$ in the weak interaction regime of a tunable, high quality, two-dimensional electron system in a GaAs/AlGaAs heterostructure. The band structure effects, modifying mass and g-factor, are carefully taken into accounts since they become appreciable for the large electron densities of the weak interaction regime. When properly normalized, $chi$ decreases monotonically from 3 to 1.1 with increasing density over our experimental range from 0.1 to $4times10^{11} cm^{-2}$. In the high density limit, $chi$ tends correctly towards $chito 1$ and compare well with recent theory.
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We calculate the spin-Hall conductivity for a two-dimensional electron gas within the self-consistent Born approximation, varying the strength and type of disorder. In the weak disorder limit we find both analytically and numerically a vanishing spin-Hall conductivity even when we allow a momentum dependent scattering. Separating the reactive from the disspative current response, we find the universal value $sigma^R_{sH} = e/8 pi$ for the reactive response, which cancels however with the dissipative part $sigma^D_{sH} = -e/8 pi$.
Electron-beam propagation experiments have been used to determine the energy and angle dependence of electron-electron (ee) scattering a two-dimensional electron gas (2DEG) in a very direct manner by a new spectroscopy method. The experimental results are in good agreement with recent theories and provide direct evidence for the differences between ee-scattering in a 2DEG as compared with 3D systems. Most conspicuous is the increased importance of small-angle scattering in a 2D system, resulting in a reduced (but energy-dependent) broadening of the electron beam.
Effects associated with the interference of electron waves around a magnetic point defect in two-dimensional electron gas with combined Rashba-Dresselhaus spin-orbit interaction in the presence of a parallel magnetic field are theoretically investigated. The effect of a magnetic field on the anisotropic spatial distribution of the local density of states and the local density of magnetization is analyzed. The existence of oscillations of the density of magnetization with scattering by a non-magnetic defect and the contribution of magnetic scattering (accompanied by spin-flip) in the local density of electron states are predicted.
We report effective hole mass ($m^{*}$) measurements through analyzing the temperature dependence of Shubnikov-de Haas oscillations in dilute (density $p sim 7 times 10^{10}$ cm$^{-2}$, $r_{s} sim 6$) two-dimensional (2D) hole systems confined to a 20 nm-wide, (311)A GaAs quantum well. The holes in this system occupy two nearly-degenerate spin subbands whose $m^{*}$ we measure to be $sim $ 0.2 (in units of the free electron mass). Despite the relatively large $r_{s}$ in our 2D system, the measured $m^{*}$ is in good agreement with the results of our energy band calculations which do not take interactions into account. We hen apply a sufficiently strong parallel magnetic field to fully depopulate one of the spin subbands, and measure $m^{*}$ for the populated subband. We find that this latter $m^{*}$ is surprisingly close to the $m^{*}$ we measure in the absence of the parallel field. We also deduce the spin susceptibility of the 2D hole system from the depopulation field, and conclude that the susceptibility is enhanced by about 50% relative to the value expected from the band calculations.
Optical orientation experiments have been performed in GaAs epilayers with photoexcitation energies in the 3 eV region yielding the photogeneration of spin-polarized electrons in the satellite L valley. We demonstrate that a significant fraction of the electron spin memory can be conserved when the electron is scattered from the L to the $Gamma$ valley following an energy relaxation of several hundreds of meV. Combining these high energy photo-excitation experiments with time-resolved photoluminescence spectroscopy of $Gamma$ valley spin-polarized photogenerated electrons allows us to deduce a typical L valley electron spin relaxation time of 200 fs, in agreement with theoretical calculations.
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