Appearance and disappearance of Majorana Zero Modes with magnetic field tilt in superconducting FeTe_1-xSe_x

Recently it was proposed that iron-chalcogenide material FeTe_1-xSe_x can host Majorana zero modes at the ends of vortex lines for a range of compositions. Due to the low density of states in FeTe_1-xSe_x, Majorana zero modes in superconducting vortices are expected to be separated by a relatively large gap from other vortex modes. On the experimental side, observation of Majorana zero modes at the ends of vortex lines has been debated. In this talk, we show that the presence of the vortex Majorana zero modes strongly depends on the direction of the vortex with respect to the crystal. By rotating the magnetic field, the vortex will go through a topological phase transition which is apparent from the appearance and disappearance of the Majorana zero modes at the ends of the vortex.