the cross sections link up with each other and form a single curve ( panel (c) ). A further increase in energy causes the the two Dirac cones overlap with each other the anti crossing of the energy levels due to the inter surface coupling causes the $k$ space lens-shaped region where the Dirac cones overlap to break away from the outer perimeter of the overlapping ‘circles’ and form a second closed curve. Despite the distortions of the EECs from the perfectly circular profiles in the absence of inter-surface coupling, the directions of the in-plane spin accumulation along the EECs in the presence of inter-surface coupling still roughly follow those of the original Dirac cones. Returning now to panel (a) of the figure, it is evident that as the inter-surface coupling increases, the energy of the lowest energy particle (hole) band at $\vec{k}=0$ increases (decreases).

![ Panel (a) shows the dispersion relations for progressively larger values of $\lambda$ indicated by the colors in the legend relative to the fixed value of $\vec{M} = 0.5\hat{y}$. Panels (b) and (c) show the EECs (in solid lines) and in-plane spin accumulation directions for $\lambda = 0.7$ at the two values of energies (0.5 