  Recent experiment reported the robust zero-energy states with strange
properties in a trilayer heterostructure MnTe/Bi2Te3/Fe(Te,Se). Here, we give
comprehensive understandings about the magnetic and electronic properties of
the heterostructure, and propose ferromagnetic Mn-Bi antisite defects are
generated in the topmost sublayer of Bi2Te3 and hidden below the MnTe layer. We
further reveal the defect can induce two types of quasiparticles. One is
Yu-Shiba-Rusinov state from defect itself, and another is Majorana zero mode
from the superconducting phase domain wall induced by the defect. The two types
of quasiparticles have very different response to magnetic field, temperature
etc. The coexistence and mutual cooperation of both can explain experimental
observations. Furthermore, we propose more simple heterostructure with
superiority to generate and finely modulate Majorana zero modes.
