Figure 8: The massive Dirac spectrum in the 2D hexagonal lattice.
From: Evidence for massive bulk Dirac fermions in Pb1−xSnxSe from Nernst and thermopower experiments
We assume distinct on-site energies on sublattices A and B (as in boron nitride). The Dirac cones sit at the high-symmetry points K and K′ on the edge of the Brillouin Zone (upper inset). In a magnetic field B, the N=0 LL at K moves to a value above E=0 (curve 1), whereas the N=0 LL at K′ moves below E=0 (curve 2). The sum of the two spectra (K+K′) is symmetric about E=0 (curves 3). However, the N=0 LLs are non-degenerate, whereas all other LLs (N≠0) have a valley degeneracy of 2. As B increases, all LLs fan out except for the N=0 levels (curves 3).
