Gapless Dirac cone surface states in 3D topological insulators — protected by time-reversal symmetry, robust against backscattering
1.2 eV
0
0.3 eV
0.3
H_surf = ℏv_F(k×σ̂)·ẑ — The surface Dirac cone is a hallmark of Z₂ topological insulators (Bi₂Se₃, Bi₂Te₃). Spin is locked to momentum, forbidding backscattering.