Superconductivity in the non-oxide perovskite MgCNi₃

Abstract

The interplay of magnetic interactions, the dimensionality of the crystal structure 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 were long thought to be detrimental to the formation of a superconducting state, they are actually common features of both the high transition-temperature (T_c) copper oxides and low-T_c material Sr₂RuO₄, where they appear to be essential contributors to the exotic electronic states of these materials¹. Here we report that the perovskite-structured compound MgCNi₃ is superconducting with a critical temperature of 8 K. This material is the three-dimensional analogue of the LnNi₂B₂C family of superconductors, which have critical temperatures up to 16 K (ref. 2). The itinerant electrons in both families of materials arise from the partial filling of the nickel d-states, which generally leads to ferromagnetism as is the case in metallic Ni. The high relative proportion of Ni in MgCNi₃ suggests that magnetic interactions are important, and the lower T_c of this three-dimensional compound—when compared to the LnNi₂B₂C family—contrasts with conventional ideas regarding the origins of superconductivity.