Layered tin-pnictides as a novel family of van der Waals-type superconductors

Superconductors with a van der Waals (vdW) structure have attracted a considerable interest because of the possibility for truly two-dimensional (2D) superconducting systems. In order to clarify the underlying mechanisms of exotic states in these compounds, further studies on a novel family of vdW-type superconductors as an alternative system are highly desirable. We recently reported the superconductivity in layered tin arsenide NaSn2As2 with transition temperature (Tc) of 1.3 K. Its crystal structure mainly consists of a buckled honeycomb network of SnAs layer bound by the vdW forces. Herein, we present the crystal structure and superconductivity of a novel material Na1-xSn2P2, having a crystal structure analogous to NaSn2As2. Amount of Na deficiency (x) was estimated to be 0.074(18) using synchrotron X-ray diffraction. Measurements of electrical resistivity and specific heat confirm the bulk nature of the superconductivity of Na1-xSn2P2 with Tc = 2.0 K. Because there are various structural analogues with tin-pnictide (SnPn) conducting layers, our results indicate that SnPn-based layered compounds can be categorized into a novel family of vdW-type superconductors, providing a new platform for studies on physics and chemistry of low-dimensional superconductors.