Ni$_2$X$_2$ (X=pnictide, chalcogenide, or B) Based Superconductors

TL;DR

This paper reviews Ni-based superconductors with Ni2X2 planes, highlighting their conventional electron-phonon pairing, structural similarities to FeAs superconductors, and discusses their properties and potential connections to Fe-based systems.

Contribution

It provides a comprehensive review of Ni2X2-based superconductors, emphasizing their conventional pairing mechanism and structural parallels with FeAs superconductors.

Findings

Evidence for fully gapped superconducting state in BaNi2As2

Ni-based compounds are likely conventional electron-phonon superconductors

Structural similarities suggest a deeper connection to FeAs superconductors

Abstract

We review the properties of Ni-based superconductors which contain Ni2X2 (X=As, P, Bi, Si, Ge, B) planes, a common structural element found also in the recently discovered FeAs superconductors. Strong evidence for the fully gapped nature of the superconducting state has come from field dependent thermal conductivity results on BaNi2As2. Coupled with the lack of magnetism, the majority of evidence suggests that the Ni-based compounds are conventional electron-phonon mediated superconductors. However, the increase in Tc in LaNiAsO with doping is anomalous, and mimics the behavior in LaFeAsO. Furthermore, comparisons of the properties of Ni- and Fe-based systems show many similarities, particularly with regards to structure-property relationships. This suggests a deeper connection between the physics of the FeAs superconductors and the related Ni-based systems which deserves further investigation.