Crystal structures and physical properties of novel 4d/5d based superconductors

The interplay among spin, orbital and lattice in a strongly-correlated electron system attracts a lot of attention in the community of condensed matter physics. The competition and collaboration of these effects result in multiple ground states, such as superconductivity, quantum criticality state, topological phase transition, metallic-insulating transition, etc. As is well known, the spin-orbital coupling is an interaction between the spin angular moment and orbit angular moment. In quantum mechanics, the spin-orbital coupling can be described as an additional interaction in the Hamitonian. For a compound containing heavy elements, the spin-orbital interaction becomes nontrival and can influence the ground states. For instance, in 4d/5d based superconductors, the superconducting pairing mechanism might be significantly different from that of conventional Bardeen-Cooper-Schrieffer superconductor. In this paper, we will summarize the structures and physical properties of several typical 4d/5d transition metal-based superconductors and discuss the intrinsic relationship between them. Importantly, the strength of anionic covalent bonds can determine the phase transition and superconductivity, which will be highlighted here.