Figure 3: Helical states near the Dirac cone.
From: Creation of helical Dirac fermions by interfacing two gapped systems of ordinary fermions
(a) Two equal-energy cuts as marked above and below Dirac point for calculating the helical Dirac states in Bi/Bi2Se3. (b) Definitions of the θ (angle between k and kx axis), φ (angle between S and kz axis) and α (angle between k and S), which are used to characterize the spin direction (S) with respect to the momentum direction (k). (c,d) In-plane spin-momentum relation in the upper and lower cut in (a), respectively. (e) Out-of-plane spin-momentum relation in the upper and lower cuts in (a). (f) Angle between spin and momentum in the upper and lower cuts in (a).
