Study on Green’s function on topological insulator surface

In the theory of superconducting junctions, Green’s function has an important role for obtaining Andreev bound states, local density of states and Josephson current in a systematic way. In this article, we show how to construct Green’s function on the surface of a topological insulator following McMillan’s formalism where the energy spectrum of electrons obeys a linear dispersion. For a model of a superconductor (S)/ferromagnet (F)/normal metal (N) junction, we show that the generation of a Majorana fermion gives rise to the enhanced local density of states and pair amplitude of odd-frequency pairing. We also derive an extended Furusaki–Tsukada’s formula of DC Josephson current in S/F/S junctions. The obtained Josephson current depends on the direction and magnitude of the magnetization. This article is part of the theme issue ‘Andreev bound states’.