Theoretical study of x-ray absorption of three-dimensional topological insulator Bi2Se3

The x-ray absorption edge singularity which is usually relevant for metals is studied for the prototype topological insulator Bi₂Se₃. The generalized integral equation of the Nozières and Dominicis type for the x-ray edge singularity is derived and solved. The spin texture of surfaces states causes a component of singularity dependent on the helicity of the spin texture. It also yields another component for which the singularity from excitonic processes is absent.