The Superconducting Phase Diagram of ThFe1−xNixAsN

Abstract

Differently from most of the other 1111-type iron-based superconductors (IBSCs), ThFeAsN without an antiferromagnetic order shows superconductivity at 30 K in the absence of chemical doping and other treating. In order to enhance its superconductivity and understand its peculiar superconducting behaviour, it is necessary to investigate the evolution of the superconducting phase through electron doping, especially heavy electron doping. Chemically, the doping of Ni is an effective way to realize heavy electron doping, as Ni atoms have two more 3d electrons than Fe atoms and electrons could be doped directly into the FeAs planes. As is known that ThFeAsN is a kind of unconventional superconductor, while ThNiAsN is a kind of conventional superconductor, then if ThFeAsN is doped with Ni to form ThFe1−xNixAsN, some intriguing behaviours such as the phase transition from unconventional superconductivity to conventional superconductivity may be observed. Here, we have synthesized ThFe1−xNixAsN with 0.01 ≤ x ≤ 1. It is found that, with doping of Ni, the superconductivity of ThFeAsN is suppressed quickly. For ThNiAsN resynthesized by us, its Tc is 4.8 K, which is higher than the previously reported value of Tc = 4.3 K. The superconducting phase diagram of ThFe1−xNixAsN is drawn to summarize the doping results. Considering the other electron doping results of ThFeAsN1−xOx and ThFe1−xCoxAsN, it can be concluded that the electron doping is not an effective way to increase the Tc of ThFeAsN. The hole doping result is expected. Being associated with the previous results, it can be concluded that the superconductivity of ThFeAsN is much more sensitive to in-plane disorder than that of doped LaFeAsO, which reveals again that their superconductivity mechanisms are really different.