Goto Yosuke, Miura Akira, Moriyoshi Chikako, Kuroiwa Yoshihiro, Matsuda Tatsuma D, Aoki Yuji, Mizuguchi Yoshikazu
Department of Physics, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo, 192-0397, Japan.
Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Sapporo, 060-8628, Japan.
Sci Rep. 2018 Aug 27;8(1):12852. doi: 10.1038/s41598-018-31295-8.
Superconductors with a van der Waals (vdW) structure have attracted a considerable interest because of the possibility for truly two-dimensional (2D) superconducting systems. We recently reported NaSnAs as a novel vdW-type superconductor with transition temperature (T) of 1.3 K. Herein, we present the crystal structure and superconductivity of new material NaSnP with T = 2.0 K. Its crystal structure consists of two layers of a buckled honeycomb network of SnP, bound by the vdW forces and separated by Na ions, as similar to that of NaSnAs. Amount of Na deficiency (x) was estimated to be 0.074(18) using synchrotron X-ray diffraction. Bulk nature of superconductivity was confirmed by the measurements of electrical resistivity, magnetic susceptibility, and specific heat. First-principles calculation using density functional theory shows that NaSnP and NaSnAs have comparable electronic structure, suggesting higher T of NaSnP resulted from increased density of states at the Fermi level due to Na deficiency. 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.
具有范德华（vdW）结构的超导体因其有可能实现真正的二维（2D）超导系统而引起了广泛关注。我们最近报道了NaSnAs作为一种新型的vdW型超导体，其转变温度（T）为1.3 K。在此，我们展示了新材料NaSnP的晶体结构和超导性，其T = 2.0 K。它的晶体结构由两层呈褶皱状的SnP蜂窝网络组成，通过范德华力结合，并由Na离子分隔，与NaSnAs的结构相似。利用同步加速器X射线衍射估计Na的缺陷量（x）为0.074(18)。通过电阻率、磁化率和比热测量证实了超导的体相性质。使用密度泛函理论的第一性原理计算表明，NaSnP和NaSnAs具有可比的电子结构，这表明NaSnP的较高T是由于Na缺陷导致费米能级处态密度增加所致。由于存在各种具有锡磷化物（SnPn）导电层的结构类似物，我们的结果表明基于SnPn的层状化合物可归类为一个新型的vdW型超导体家族，为低维超导体的物理和化学研究提供了一个新平台。
