Npj Comput. Mater.: 超导与拓扑共存—Kagome金属

海归学者发起的公益学术平台

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交流学术，偶尔风月

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。

Fig.1 Crystal structure of ANb₃Bi₅(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 of ANb₃Bi₅(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 for ANb₃Bi₅(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 for ANb₃Bi₅(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 metals ANb₃Bi₅(A = K, Rb, Cs) (Kagome金属ANb₃Bi₅

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

TheAV₃Sb₅ prototype 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 that ANb₃Bi₅ (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 of ANb₃Bi₅ (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 Z₂ topological 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 in ANb₃Bi₅ (A = K, Rb, Cs) offer us more insights to study the relationship between superconductivity and topological properties, and to design innate topological superconductors.