Superconductivity in the non-oxide perovskite MgCNi3

The interplay of magnetic interactions, the dimensionality of the crystal s tructure and electronic correlations in producing superconductivity is one of the dominant themes in the study of the electronic properties of complex materials. Although magnetic interactions and two-dimensional structures w ere long thought to be detrimental to the formation of a superconducting st ate, they are actually common features of both the high transition-temperat ure (T-c) copper oxides and low-T-c material Sr2RuO4, where they appear to be essential contributors to the exotic electronic states of these material s(1). Here we report that the perovskite-structured compound MgCNi3 is supe rconducting with a critical temperature of 8 K. This material is the three- dimensional analogue of the LnNi(2)B(2)C family of superconductors, which h ave critical temperatures up to 16 K (ref. 2). The itinerant electrons in b oth families of materials arise from the partial filling of the nickel d-st ates, which generally leads to ferromagnetism as is the case in metallic Ni . The high relative proportion of Ni in MgCNi3 suggests that magnetic inter actions are important, and the lower T-c of this three-dimensional compound -when compared to the LnNi(2)B(2)C family-contrasts with conventional ideas regarding the origins of superconductivity.