Full Electrical Control of the Electron Spin Relaxation in GaAs Quantum Wells

The electron spin dynamics in (111)-oriented $\mathrm{GaAs}/\mathrm{AlGaAs}$ quantum wells is studied by time-resolved photoluminescence spectroscopy. By applying an external electric field of $50\mathrm{kV}/\mathrm{cm}$ a two-order of magnitude increase of the spin relaxation time can be observed reaching values larger than 30 ns; this is a consequence of the electric field tuning of the spin-orbit conduction band splitting which can almost vanish when the Rashba term compensates exactly the Dresselhaus one. The measurements under a transverse magnetic field demonstrate that the electron spin relaxation time for the three space directions can be tuned simultaneously with the applied electric field.

Figure 1

(a) PIN $\mathrm{GaAs}/\mathrm{AlGaAs}$ MQW structure. $E$ is positive when it points along the growth direction. (b) Circular polarization dynamics for different reverse bias voltages $V$ for sample I ($L=15\mathrm{nm}$). Inset: Dependence of the electron spin relaxation time with the electric field for samples I and III ($L=7.5\mathrm{nm}$).

Figure 2

Sample II (NIP). (a) Electron spin dynamics at $T=50\mathrm{K}$ for different reverse voltages. Inset: Schematic of the BIA (${\mathbf{\Omega }}_{\mathbf{B}\mathbf{I}\mathbf{A}}$) and SIA (${\mathbf{\Omega }}_{\mathbf{S}\mathbf{I}\mathbf{A}}$) precession vectors in (111) GaAs quantum wells. $\mathit{S}$ is the photogenerated electron spin at $t=0$. (b) Dependence of the electron spin relaxation times ${\tau }_s^z$ (circles), ${\tau }_s^y$ (triangles), ${\tau }_s^x$ (squares), as a function of the electric field. Inset: PL circular polarization dynamics for $B_x=0$ and $B_x=0.26\mathrm{T}$ ($V=-3.5\mathrm{V}$, see arrow). The $P_c$ dynamics for $V=0$ and $B_x=0$ is also displayed.