Two-dimensional (2D) topological superconductors are highly desired because they not only offer opportunities for exploring novel exotic quantum physics but also possess potential applications in quantum computation. However, there are few reports about 2D superconductors, let alone topological superconductors. Here, we find a 2D monolayer ${\mathrm{W}}_2{\mathrm{N}}_3$, which can be exfoliated from its real van der Waals bulk material with much lower exfoliation energy than ${\mathrm{MoS}}_2$, to be a topological metal with exotic topological states at different energy levels. Owing to the Van Hove singularities, the density of states near the Fermi level are high, making the monolayer a compensate metal. Moreover, the monolayer ${\mathrm{W}}_2{\mathrm{N}}_3$ is unveiled to be a superconductor with the superconducting transition temperature $T_C$ $\sim$ 22 K and a superconducting gap of about 5 meV based on the anisotropic Migdal-Eliashberg formalism, arising from the strong electron-phonon coupling around the $\mathrm{\Gamma }$ point, and the 2D superconductor is phonon mediated and fits the BCS mechanism with an Ising-type pairing. Because of the strong electron and lattice coupling, the monolayer displays a non-Fermi liquid behavior in its normal states at temperatures lower than 80 K, where the specific heat exhibits $T^3$ behavior and the Wiedemann-Franz law is dramatically violated. Our findings not only provide a platform to study the emergent phenomena in 2D topological superconductors, but also open a door to discover more 2D high-temperature topological superconductors in van der Waals materials.

中文翻译：

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Van der Waals层状材料中的二维拓扑超导候选

二维（2D）拓扑超导体是非常需要的，因为它们不仅为探索新颖的奇异量子物理学提供了机会，而且在量子计算中具有潜在的应用。但是，关于二维超导体的报道很少，更不用说拓扑超导体了。在这里，我们找到了二维单层${\mathrm{w\; ^}}_{\mathrm{2个}}{\mathrm{ñ}}_3$可以从其真正的范德华散装材料中剥落，剥落能量比 ${\mathrm{硫化钼}}_{\mathrm{2个}}$，成为在不同能级具有奇异拓扑状态的拓扑金属。由于Van Hove的奇异性，费米能级附近的态密度很高，从而使单层成为补偿金属。而且，单层${\mathrm{w\; ^}}_{\mathrm{2个}}{\mathrm{ñ}}_3$ 被宣布是具有超导转变温度的超导体 ${Ť}_C$ $〜$ 22 K和基于各向异性Migdal-Eliashberg形式论的约5 meV的超导能隙，这是由电子在周围的强声子耦合引起的。 $\mathrm{\Gamma }$点，二维超导体是声子介导的，并以伊辛型配对适合BCS机制。由于强的电子和晶格耦合，单层在低于80 K的温度下在正常状态下表现出非费米液体行为，在该温度下比热表现为${Ť}^3$行为和Wiedemann-Franz法则被严重违反。我们的发现不仅为研究二维拓扑超导体中出现的现象提供了平台，而且为在范德华材料中发现更多的二维高温拓扑超导体打开了大门。