direction for a point on the + (-) Fermi circle. The passage of an electric field in the $y$ direction causes $\langle p_y \rangle$ to increase while $\langle p_x \rangle$ remains constant, so that the SOI field $\pm (\vec{k}\times\hat{z})$ as well as the spin accumulation rotates in opposite directions for the $\pm$ Fermi circles. Reminiscent of our earlier discussion on spin 1/2 systems, this rotation in turn indicates the existence of an out of plane effective magnetic field which in turn imparts an out of plane spin accumulation. Applying the same argument to most of the other $k$-space points on the EECs in the figure explains the *sign* of the out of plane spin accumulation there. The *magnitude* of the spin $z$ accumulation depends on how much relative change in the SOI field direction the application of the electric field leads to. For example, in the right panels of the figure, the largest spin $z$ accumulation are on those EEC segments where the in-plane spin accumulation are in the $\pm y$ directions so that the small increment in the SOI field in the $\pm x$ directions due to the $y$ electric field is a large increment compared to other $k$ 