Ni-based superconductor: Heusler compound ZrNi₂Ga

This work reports on the Heusler superconductor ZrNi2 Ga. Compared to other nickel-based superconductors with Heusler structure, ZrNi2 Ga exhibits a relatively high superconducting transition temperature of Tc =2.9 K and an upper critical field of μ0 Hc2 =1.5 T. Electronic structure calculations show that this relatively high Tc is caused by a Van Hove singularity, which leads to an enhanced density of states at the Fermi energy N (∈F). The Van Hove singularity originates from a higher-order valence instability at the L point in the electronic structure. The enhanced N (∈F) was confirmed by specific-heat and susceptibility measurements. Although many Heusler compounds are ferromagnetic, our measurements of ZrNi2 Ga indicate a paramagnetic state above Tc and could not reveal any traces of magnetic order down to temperatures of at least 0.35 K. We investigated in detail the superconducting state with specific-heat, magnetization, and resistivity measurements. The resulting data show the typical behavior of a conventional weakly coupled BCS (s -wave) superconductor.