Npj Comput. Mater.: 超导与拓扑共存—Kagome金属

Kagome晶格是由两个共享顶角的三角形构成的，电子结构展示出平带、范霍夫奇点以及Dirac点，因而具有十分丰富的物性。2019年，AV3Sb5体系成功被合成，并发现具有电荷密度波、非平庸拓扑性质、独特的压力依赖的超导相图激起了人们对于以AV3Sb5为原型的材料探索热潮。以AV3Sb5为原型的Kagome金属材料因其具有电荷密度波、超导电性、非平庸的电子态以及拓扑超导电性成为了凝聚态物理学探索新奇物性的理想平台。为了减少实验的盲目性，理论预测新型可能被合成的AV3Sb5系列材料与物性显得十分重要。

来自中国科学院物理研究所/松山湖材料实验室的孟胜研究员、刘淼研究员与徐纪玉副研究员领导的团队通过第一性原理计算的方式提出了一类具有热力学、动力学稳定的Kagome金属ANb3Bi5(A= K, Rb, Cs)，并发发现体系同时具有超导电性与非平庸电子性质。

他们通过系统的理论计算，探索了体系的稳定性、超导电性以及拓扑性质。研究结果表明：(1) 考虑单质、二元化合物等形成能计算均为负，声子谱并无虚频，表明体系具有良好的热力学及动力学稳定性；(2) 基于Allen-Dynes修正的McMillan公式，计算发现KNb3Bi5, RbNb3Bi5和CsNb3Bi5分别具有2.11, 2.15 和2.21 K的超导转变温度；(3) 通过能带宇称性计算了体系的Z2指数，结合费米能级附近具有明显的表面态可以将体系归结为Z2金属。这些结果为实验探索新型Kagme材料提供了有益指引。该研究为探索超导电性、非平庸电子性质与拓扑超导之间关联性提供了新的研究平台。

该文近期发表于npjComputational Materials10：96(2024)，英文标题与摘要如下，点击https://www.nature.com/articles/s41524-024-01291-w可以自由获取论文PDF。

Fig.1 Crystal structure ofANb3Bi5(A= K, Rb, Cs).

ANb3Bi5(A= K, Rb, Cs) 晶体结构的(a)侧视图与(b)俯视图。

Fig.2 Phonon dispersions ofANb3Bi5(A= K, Rb, Cs) weighted by different atomic vibrational modes and the magnitude of the phonon linewidth.

(a)-(c) 原子振动模式分辨的声子谱及声子态密度。(d)-(f) 声子线宽权重的声子谱，Eliashberg谱函数及积分电声耦合强度。

Fig.3 Band structures without SOC forANb3Bi5(A= K, Rb, Cs).

ANb3Bi5(A= K, Rb, Cs)体系不考虑自选轨道耦效应的原子轨道分辨的能带结构及态密度。

Fig.4 Band structures with SOC forANb3Bi5(A= K, Rb, Cs).

ANb3Bi5(A= K, Rb, Cs)体系考虑自选轨道耦合效应的能带结构。阴影部分为连续能隙。

Fig.5 Surface states of KNb3Bi5.

(a)-(b) KNb3Bi5体系表面态。(c)-(d)表面态对应的等能面示意图。

Coexistence of superconductivity and topological phase in kagome metalsANb3Bi5(A= K, Rb, Cs) (Kagome金属ANb3Bi5

Jianguo Si, Lanting Shi, Bozhu Chen, Huanhuan Yang, Jiyu Xu, Miao Liu & Sheng Meng

TheAV3Sb5prototype kagome materials have been demonstrated as a versatile platform for exploring exotic properties in condensed matter physics, including charge density waves, superconductivity, non-trivial electron topology, as well as topological superconductivity. Here we identify thatANb3Bi5(A= K, Rb, Cs) exhibit non-trivial coexisting superconductivity and topological properties via first-principles calculations. The negative formation energy and the absence of imaginary phonon dispersion demonstrate both thermodynamics and dynamics stabilities ofANb3Bi5(A= K, Rb, Cs) under ambient conditions. By analytically solving the Allen-Dynes-modified McMillan formula, the superconducting transition temperatures are predicted to be 2.11, 2.15 and 2.21 K for KNb3Bi5, RbNb3Bi5, and CsNb3Bi5, respectively. More importantly, the kagome materials proposed here can be classified into Z2topological metals due to the non-trivial topological index and the obvious surface states around the Fermi level. Such coexistence of superconductivity and non-trivial band characters inANb3Bi5(A= K, Rb, Cs) offer us more insights to study the relationship between superconductivity and topological properties, and to design innate topological superconductors.