Imaging the two-component nature of Dirac–Landau levels in the topological surface state of Bi2Se3

The electrons associated with the conducting surface states of topological insulators are described by a two-component wavefunction. Experiments on Bi 2 Se 3 now show that the structure of Landau levels reflects this two-component nature. Massless Dirac electrons in condensed matter 1 , 2 , 3 , 4 , 5 , 6 are, unlike conventional electrons, described by two-component wavefunctions associated with the spin degrees of freedom in the surface state of topological insulators 5 , 6 . Hence, the ability to observe the two-component wavefunction is useful for exploring novel spin phenomena. Here we show that the two-component nature is manifest in Landau levels, the degeneracy of which is lifted by a Coulomb potential. Using spectroscopic-imaging scanning tunnelling microscopy, we visualize energy and spatial structures of Landau levels in Bi 2 Se 3 , a prototypical topological insulator. The observed Landau-level splitting and internal structures of Landau orbits are distinct from those in a conventional electron system 7 and are well reproduced by a two-component model Dirac Hamiltonian. Our model further predicts energy-dependent spin-magnetization textures in a potential variation and provides a way for manipulating spins in the topological surface state.