标题： $X$型电子化合物具有类皮肤间隙电子态和掺杂增强超导性 显示英文标题

标题： $X$-type electrides hosting skin-like interstitial electron states and doping-enhanced superconductivity

摘要： 由于碱土金属间化合物电介质独特的性质来源于间隙阴离子电子，因此它们的探索对于基础物理具有重要意义。 在这里，我们报告了一类新型的$X$型电介质，其特征在于由两种不同的阴离子电子亚通道在实空间中形成交替链。 通过结构对称性分析和第一性原理计算，我们确定二维$M_2$N ($M$ = Ti, Zr, Hf) 材料为展示这些独特特性的原型系统。 这些材料上下表面的阴离子电子通道显示出垂直交替模式，其投影带在倒空间中显示出与动量相关的分裂行为，并受到晶体对称操作$O$的保护。 值得注意的是，$X$型电介质特性独立于层数，在层状结构的上下面上仍然稳健存在，表现出明显的类似皮肤的效果。 此外，我们还研究了这些体系的超导性，发现Ti$_2$N和Zr$_2$N均为本征超导体，其超导转变温度均低于1.0 K。进一步研究表明，适当的空穴掺杂能够显著提高它们的超导转变温度，并可诱导Hf$_2$N单层表现出超导性。 我们的研究结果为设计和调整具有增强超导性能的新颖电晶质提供了宝贵的见解，为深入理解新型材料中电晶质行为与超导性之间的相互作用开辟了一条新途径。 显示英文摘要

摘要： The exploration of electrides is of great significance for the fundamental physics due to their unique properties arising from interstitial anionic electrons. Here we report a novel class of $X$-type electrides, distinguished by two distinct anionic electron subchannels forming alternating chains in real space. Through structural symmetry analysis and first-principles calculations, we identify two-dimensional $M_2$N ($M$ = Ti, Zr, Hf) materials as prototypical systems exhibiting these unique features. The anionic electron channels on the upper and lower surfaces of these materials display a vertically alternating pattern, with their projected bands revealing momentum-dependent splitting behavior in the reciprocal space, protected by a crystal symmetry operation $O$. Notably, the $X$-type electride characteristic is independent of the layer number and remains robust on the upper and lower surfaces of layered structures, presenting a pronounced skin-like effect. Additionally, we have explored the superconductivity of these systems, and found that both Ti$_2$N and Zr$_2$N are intrinsic superconductors with superconducting transition temperatures below 1.0 K. Further results show that appropriate hole doping can significantly enhance their superconducting transition temperatures and can induce the Hf$_2$N monolayer to exhibit superconductivity. Our findings provide valuable insights into the design and tuning of novel electrides with enhanced superconducting properties, offering a new pathway for deeply understanding the interplay between electride behavior and superconductivity in novel materials.