Coherence Control of Hall Charge and Spin Currents

Using two-color optical coherence control techniques in intrinsic GaAs at 80 K with orthogonally polarized 70 fs, 1430 and 715 nm pulses, we generate a pure spin source current that yields a transverse Hall pure charge current; or alternatively, with parallel polarized pulses, we generate a pure charge source current that yields a pure spin current. By varying the relative phase or polarization of the incident pulses, one can effectively tune the type, magnitude and direction of both the source and transverse currents without application of electric or magnetic fields.

Figure 1

(a) Illustration of orthogonally polarized $\omega$ and $2\omega$ pulses producing a pure spin current (double headed straight arrow) along $\omega$ beam polarization direction ($\widehat{x}$). A Hall charge current (curved arrows) and a transverse QUIC charge current along $\widehat{y}$ lead to electron accumulation near one edge of the illuminated region. (b) Same as (a) except for collinearly polarized pulses producing a QUIC charge current along $\widehat{x}$ and leading to a Hall pure spin current (curved arrows) and a transverse QUIC pure spin current (double headed arrow) resulting in up and down spin accumulations along $\pm \widehat{y}$. Inset: schematic showing how $\omega$ and $2\omega$ pulses connect valence and conduction band states for current generation.

Figure 2

(a) Contour map showing dependence of $\Delta S$ induced by a source spin current on $\Delta \varphi$ and position along $\widehat{x}$ ($y=0$). (b) Corresponding contour map of combined Hall and QUIC $\Delta N$ measured along $\widehat{y}$ ($x=0$).

Figure 3

Spatial contour maps showing: (a) the spin $\Delta S$ and (b) the charge $\Delta N$ accumulations for $\Delta \varphi =0$ associated with the pure spin source and Hall charge currents, respectively; (c) and (d) show $\Delta S$ and $\Delta N$ for $\Delta \varphi =\pi /2$, when the pure spin source current is zero and only a transverse QUIC charge current is present. Approximate spin and charge densities can be obtained by multiplying $\Delta S$ and $\Delta N$ by ${10}^{15}{\mathrm{cm}}^{-3}$.

Figure 4

(a) $N$ (circles) and $\Delta N$ (squares) caused by the source charge current and measured along $\widehat{x}$ with $\Delta \varphi =\pi /2$, for which the source current is maximum. (b) $N$ (circles) and $\Delta S$ (squares) caused by the transverse pure spin current and measured along $\widehat{y}$ with $\Delta \varphi =0.12\pi$, for which $\Delta S$ is a maximum.