Item

Abstract

This work reports on the Heusler superconductor ZrNi(2)Ga. Compared to other nickel-based superconductors with Heusler structure, ZrNi2Ga exhibits a relatively high superconducting transition temperature of T(c) = 2.9 K and an upper critical field of mu(0)H(c2) = 1.5 T. Electronic structure calculations show that this relatively high T(c) is caused by a Van Hove singularity, which leads to an enhanced density of states at the Fermi energy N(epsilon(F)). The Van Hove singularity originates from a higher-order valence instability at the L point in the electronic structure. The enhanced N(epsilon(F)) was confirmed by specific-heat and susceptibility measurements. Although many Heusler compounds are ferromagnetic, our measurements of ZrNi2Ga indicate a paramagnetic state above T(c) 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.