Magnetism and Spin-Orbit Coupling in Iron Cbalcogenide Superconductors

A prominent feature in iron-based superconductors is the strong interplay between superconductivity, magnetism, and spin-orbit coupling, which are key ingredients to promote topological states for fault-tolerant quantum computing, including Majorana zero modes (MZMs). While MZMs have been reported recently in FeTe0.55Se0.45, the topological features, magnetism, and superconductivity are found not uniformly across samples. Here, we discuss transport measurements and angle-resolved photoemission spectroscopy to characterize the electronic states in a series of (Fe, Ni)Te0.55Se0.45, Substituting Ni on the Fe site modifies spin-orbit coupling. We found Ni substitution lowers the superconducting transition temperature and changes the electronic structure and related topological properties. Our investigations suggest the presence of superconductivity and other competing ground states in (Fe, Ni)Te0.55Se0.45 Thus, the ground state control appears to be a prerequisite for the use of MZMs in quantum applications.