科研之友
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摘要
The Dirac fermions at the surface of a topological insulator can be gapped by introducing magnetic dopants. Alternatively, in an ultrathin slab with thickness on the order of the extent of the surface states, both the top and bottom surface states acquire a common gap value (Delta) but with opposite sign. In a topological insulator, the dominant piece of the Hamiltonian ((H) over cap) is of a relativistic nature. A subdominant nonrelativistic piece is also present and, in an external magnetic field (B) applied perpendicular to the surface, the N = 0 Landau level is no longer at zero energy but is shifted to positive energy by the Schrodinger magnetic energy. When a gap is present, it further shifts this level down by - Lambda for positive Lambda and up by vertical bar Lambda vertical bar for a negative gap. This has important consequences for the magneto-optical properties of such systems. In particular, at charge neutrality, the lowest energy transition displays anomalous nonmonotonic behavior as a function of B in both its position in energy and its optical spectral weight. The gap can also have a profound impact on the spectral weight of the interband lines and on corresponding structures in the real part of the dynamical Hall conductivity. Conversely, the interband background in zero field remains unchanged by the nonrelativistic term in (H) over cap (although its onset frequency is modified).
- 出版日期2015-12-10
