Chiral photoluminescence in topological insulators

In topological insulators, the strong SOC, in combination with the time-reversal symmetry, leads to the protected metallic surface states. These states have opposite spins and propagate in opposite directions, forming a spin current as it occurs in the spin Hall effect. The surface states from this spin-dependent quantum Hall effect consist of counterpropagating states (called helical states) with opposite spins. The penetration depth of these states is of the order of the lattice constant if the surface states extend almost over the whole Brillouin zone (BZ). Theoretical and experimental studies show that there are two more surface bands near the Brillouin zone center (Γ-point) in Bi₂Se₃, a high-energy unoccupied Dirac cone (SS2) and a fully occupied Rashba-like surface state (RSS). Thus far, less is known about the properties of RSS and SS2. We will use photoluminescence spectroscopy to investigate the properties of these states (SS2 and RSS) under different excitation photon energies and polarizations.