标题： 二维非范德华铌氮化物纳米片中的高温双能隙超导性 显示英文标题

标题： Two-dimensional non-van der Waals niobium nitride nanosheets with high-temperature two-gap superconductivity

摘要： 二维材料中超导性的探索由于其在低功耗应用和基础科学兴趣方面的前景而引起了广泛关注。 在这里，我们报告了一些通过第一性原理计算确定的从沿(001)平面剥离的NbN块体中衍生出的新型稳定非范德华力Nb$_x$N$_{x+1}$ ($x$ = 1-4) 单层结构。 在这些单层结构中，Nb$_2$N$_3$，其在$P \overline{6} m2$对称性下结晶，具有77.8 K的异常高的超导转变温度，为二维过渡金属氮化物和二元化合物设定了新的高$T_c$基准。 我们的详细分析表明，Nb$_2$N$_3$中的强超导性是由以N振动为主的声子模式驱动的，N-$p$和Nb-$d$电子态对电子-声子耦合有显著贡献。 利用各向异性 Migdal-Eliashberg 框架，我们进一步确定了 Nb$_2$N$_3$单层中的双能隙超导特性，其特征是明显的电子-声子耦合和各向异性能隙。 这些结果加深了我们对二维过渡金属氮化物中超导性的理解，并突显了它们在纳米尺度超导应用中的潜力。 显示英文摘要

摘要： The exploration of the superconductivity in two-dimensional materials has garnered significant attention due to their promising low-power applications and fundamental scientific interest. Here, we report some novel stable non-van der Waals Nb$_x$N$_{x+1}$ ($x$ = 1-4) monolayers derived from the NbN bulk exfoliated along the (001) plane, as identified through first-principles calculations. Among these monolayers, Nb$_2$N$_3$, which crystallizes in the $P \overline{6} m2$ symmetry, stands out with an exceptional superconducting transition temperature of 77.8 K, setting a new high-$T_c$ benchmark for two-dimensional transition metal nitrides and binary compounds. Our detailed analysis reveals that the strong superconductivity in Nb$_2$N$_3$ is driven by phonon modes dominated by N vibrations, with significant electron-phonon coupling contributions from N-$p$ and Nb-$d$ electronic states. Using the anisotropic Migdal-Eliashberg framework, we further determine the two-gap nature of the superconductivity in the Nb$_2$N$_3$ monolayer, characterized by pronounced electron-phonon coupling and anisotropic energy gaps. These results advance our understanding of superconductivity in 2D transition metal nitride and highlight their potential for nanoscale superconducting applications.