Element substitution effects on superconductivity and charge density wave of Laves compound ZrV₂

Laves-phase compounds ZrV₂ and HfV₂ have C15-type cubic crystal structure, which contains V sublattice of corner-sharing tetrahedra (pyrochlore lattice). These compounds exhibit superconducting and charge-density-wave (CDW) transitions at T_c ~ 9 K and T_CDW ~ 120 K, respectively. Concerning the superconductivity of ZrV₂ and HfV₂, the NMR study suggested the presence of point nodes in the superconducting gap. To study element substitution effects on the superconductivity and CDW of ZrV₂ and HfV₂, we investigate structural, electric, and magnetic properties of polycrystalline (Zr_1-xHf_x)V₂ and Zr(V_1-xCr_x)₂ (x = 0 ~ 1). The experiments reveal that (Zr_1-xHf_x)V₂ exhibits superconductivity and CDW order regardless of the Hf concentration x. For Zr(V_1-xCr_x)₂, on the other hand, superconductivity and CDW order are found to be suppress with increasing Cr concentration x. These results suggest that, for ZrV₂ and HfV₂, V 3d electrons play dominant roles for the occurrence of superconductivity and CDW order. Furthermore, the experiments in Zr(V_1-xCr_x)₂ reveal that the Cr doping suppresses the CDW order more sensitively than the superconductivity, which implies that, for ZrV₂ and HfV₂, the superconducting and CDW gaps respectively open on different portions of the Fermi surface.