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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.
