(a) The variation of the magnitude of the current-induced spin polarization density at a sample point (defined by |k_Fx| = 50) in SM with the increase of the bias voltage. (b) The corresponding variation of the charge current density with the increase of the bias voltage. The parameters are: Δ/E_F = 0.001, Z = 1, β =0, and α is shown in the inset of the figures. For the cases of β =0, the direction of the current-induced spin polarization is parallel to the y axis. If both α and β are not zero, both x and y components of the spin polarization will be non-vanishing. In such cases the variation of the spin polarization density with the increase of the bias voltage is still similar to that as shown in Fig. 1(a) and hence not shown explicitly.