Fe(1+y )Te( x )Se1-( x ): A Delicate and Tunable Majorana Material

We report the observation for the p(z) electron band and the band inversion in Fe1 + y Te x Se1-x with angle-resolved photoemission spectroscopy. Furthermore, we found that excess Fe (y > 0) inhibits the topological band inversion in Fe1 + y Te x Se1 - x , which explains the absence of Majorana zero modes in previous reports for Fe1+y Te x Se1 - x with excess Fe. Based on our analysis of different amounts of Te doping and excess Fe, we propose a delicate topological phase in this material. Thanks to this delicate phase, one may be able to tune the topological transition via applying lattice strain or carrier doping.