Particle-hole asymmetry and quantum confinement effects on the magneto-optical response of topological insulator thin-films

Intrinsically broken symmetries in the bulk of topological insulators (TIs) are manifested in their surface states. Despite particle-hole asymmetry in TIs, it has often been assumed that their surface states are characterized by a particle-hole symmetric Dirac energy dispersion. In this work, we demonstrate that the effect of particle-hole asymmetry is essential to correctly describe the energy spectrum and the magneto-optical response in TIs thin-films. In thin-films of TIs with a substantial degree of particle-hole symmetry breaking, such as Sb 2Te 3, the longitudinal optical conductivity displays absorption peaks arising from optical transitions between bulk and surface Landau levels for low photon energies. The transition energies between the bulk and surface Landau levels exhibit clearly discernable signatures from those between surface Landau levels due to their distinct magnetic field dependence. Bulk contributions to the magneto-optical conductivity in a TI thin-film are enhanced via one type of doping while being suppressed by the other. This asymmetric dependence on the type of doping aids in revealing the particle-hole asymmetry in TI thin-films.

Automated summary

This work demonstrates the essential role of particle-hole asymmetry in describing the energy spectrum and magneto-optical response in thin-films of topological insulators (TIs). The longitudinal optical conductivity in TIs with substantial particle-hole symmetry breaking exhibits absorption peaks arising from optical transitions between bulk and surface Landau levels. The transition energies between these levels show distinct magnetic field dependence, revealing the particle-hole asymmetry in TI thin-films.