Spectral Dependence of Spin Photocurrent and Current-Induced Spin Polarization in an $\mathrm{InGaAs}/\mathrm{InAlAs}$ Two-Dimensional Electron Gas

The converse effects of spin photocurrent and current induced spin polarization are experimentally demonstrated in a two-dimensional electron gas system with Rashba spin splitting. Their consistency with the strength of the Rashba coupling as measured for the same system from beating of the Shubnikov–de Haas oscillations reveals a unified picture for the spin photocurrent, current-induced spin-polarization, and spin-orbit coupling. In addition, the observed spectral inversion of the spin photocurrent indicates a system with dominating structure inversion asymmetry.

Figure 1

(a) and (b) are the beating patterns of the SdH oscillations at 1.6 K under low magnetic field as shown in the first derivative of the magneto-resistance $R_{xx}$ of samples D and E, respectively. (c) and (d) are the calculated carrier concentrations based on the FFT spectrum from (a) and (b).

Figure 2

(a) and (b) are the angle $\varphi$ dependence of the spin photocurrent in the 2DEG sample D and E, respectively, with oblique incidence angle of 30° and laser power of 100 mW ($\lambda =880\mathrm{nm}$) at 10 K, showing the helicity dependence of the photocurrent. The solid lines are the fit using $\sin 2\varphi$. (c) is a schematic diagram with spin-split valence and conduction bands to show the microscopic origin of the CPGE induced photocurrent. The vertical arrows show the permitted transitions with ${\sigma }^{-}$ excitation and the horizontal arrow indicates the final direction of the induced photocurrent. (d) is the incidence angle $\Theta$ dependence of the photocurrent. The solid line is the fitted curve. The experimental setup of the spin photocurrent is depicted in the inset.

Figure 3

Spectral response of the spin photocurrent for (a) sample D and (b) sample E. The photoreflectance spectra of the two samples are also shown to determine the electronic structures of the samples. The arrows indicate the heavy hole (hh) and light hole (lh) related transitions.

Figure 4

Electric field ($E_x$) dependence of the Kerr rotation of sample D (a) and E (b) to show the current-induced spin polarization $⟨S_y⟩$ at 10 K. The temperature dependence of the Kerr rotation of sample D ($E_x=50\mathrm{V}/\mathrm{cm}$) is shown in the inset of Fig. 4a. The experimental setup is schematically shown in the inset of Fig. 4b, of which $P1$ and $P2$ represent the polarizer and analyzer, respectively.