Split Dirac cones in HgTe/CdTe quantum wells due to symmetry-enforced level anticrossing at interfaces

HgTeisaband-invertedcompoundwhichformsatwo-dimensionaltopologicalinsulatorifsandwichedbetween CdTe barriers for a HgTe layer thickness above the critical value. We describe the fine structure of Dirac states in the HgTe/CdTe quantum wells of critical and close-to-critical thicknesses and show that the necessary creation of interfaces brings in another important physical effect: the opening of a significant anticrossing gap between the tips of the Dirac cones. The level repulsion driven by the natural interface inversion asymmetry of zinc-blende heterostructures considerably modifies the electron states and dispersion but preserves the topological transition at the critical thickness. By combining symmetry analysis, atomistic calculations, and extended k · p theory with interface terms, we obtain a quantitative description of the energy spectrum and extract the interface mixing coefficient. Wediscusshowthefingerprintsofthepredictedzero-magnetic-field splittingoftheDiraccones could be detected experimentally by studying magnetotransport phenomena, cyclotron resonance, Raman scattering, and THz radiation absorption.