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

TL;DR

This paper investigates how particle-hole asymmetry and quantum confinement influence the magneto-optical response of topological insulator thin-films, revealing distinct optical transition signatures and doping-dependent effects.

Contribution

It demonstrates the importance of particle-hole asymmetry in accurately modeling the energy spectrum and magneto-optical properties of TI thin-films, especially in materials like Sb$_2$Te$_3$.

Findings

Optical absorption peaks from bulk-surface Landau level transitions.

Distinct magnetic field dependence of transition energies.

Doping modifies bulk contributions to magneto-optical conductivity.

Abstract

Intrinsically broken symmetries in the bulk of topological insulators (TIs) are manifested in their surface states. In spite of 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$_2$Te$_3$, 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 type of doping aids in revealing the particle-hole asymmetry in TI thin-films.