Topological superconductor candidates PdBi2Te4 and PdBi2Te5 from a generic ab initio strategy
Aiyun Luo, Ying Li, Yi Qin, Jingnan Hu, Xiaoxu Wang, Jinyu Zou, Biao Lian & Gang Xu
npj Computational Materials 9: 188 (2023)
doi.org/10.1038/s41524-023-01144-y
Published online: 13 October 2023
编辑概述
拓扑超导设计新策略和新方法
马约拉纳零能模可以应用于非阿贝尔量子门操作中，速度是现存量子计算的103倍。超导拓扑金属是实现马约拉纳零能模的理想平台。但现有大多数超导拓扑金属的能带结构非常复杂，拓扑表面态埋在体能带中难以形成实现拓扑超导需要的配对。另一方面，由于缺少从第一性原理出发计算拓扑超导性质的普适程序，也严重限制了从现有超导拓扑金属中挑选和调控实现拓扑超导的可能。在本工作中，华中科技大学国家脉冲强磁场科学中心的徐刚教授团队提出了一种在拓扑绝缘体中插层超导单元来设计拓扑超导金属的新范式，开发了一套基于第一性原理计算表征拓扑超导不变量的通用程序，提出了实验上可合成的理想候选材料PdBi2Te5和PdBi2Te4。团队通过调研发现Bi2Te3拓扑绝缘体和PdTe2 、PdTe超导体具有相同的晶格构型和相近的面内晶格常数，因而可以通过插层得到拓扑超导金属PdBi2Te5和PdBi2Te4。他们通过形成能和声子计算确认了材料的热力学稳定性和动力学稳定性，在实验上易于合成。进一步的电子结构计算表明其能带结构很好地继承了Bi2Te3的能带反转和拓扑能隙，并在费米能级处呈现出拓扑表面态。电声耦合的计算则发现候选材料继承了PdTe2 、PdTe的超导性，超导转变温度分别为0.57K和3.11K。团队进一步利用新开发的计算程序，构造了PdBi2Te5和PdBi2Te4的二维薄膜 BdG哈密顿量，计算了在表面引入塞曼劈裂下的超导能谱和拓扑不变量，确认了其手性拓扑超导态。该研究工作为设计和调控拓扑超导材料提供了新的思路和工具，也为制备拓扑超导量子器件提供了理论指导。
Editorial Summary
The new strategy and method of topological superconductivity design
The Majorana zero modes can be applied to realize non-Abelian quantum gate operations, which could be 103 faster than the currently existing quantum computation schemes. Superconducting topological metal is an ideal platform to realize Majorana zero modes. However, its band structure is rather complicated with topological surface states buried in the bulk states, and difficult to form the pairing required by topological superconductor. On the other hand, an ab initio program to calculate the topological superconductor properties of superconducting topological metal is still not accessible, restricting the searching of topological superconductor. The group lead by professor Gang Xu from Huazhong University of Science and Technology proposed a new strategy to design superconducting topological metals by intercalating the superconducting units into the topological insulators, developed a program that characterizes the superconducting BdG Chern number of 2D BdG Hamiltonian from ab initio calculations, and put forward the experimental realizable ideal candidates PdBi2Te5 and PdBi2Te4. They found that the Bi2Te3 topologicial insulator and PdTe2, PdTe superconductor possess the same crystal structure and similar in-plane lattice constant, which makes it reasonable to construct PdBi2Te5 and PdBi2Te4 through the method of intercalating. The calculation of formation energy and phonon confirm the thermal and dynamical stability, hence the materials are accessible in experiments. The calculation of the electron structure shows that the bands inherit the band inversion and topological gap of Bi2Te3, and exhibit the surface states at the Fermi energy. The calculation of the electron-phonon coupling demonstrates that the superconductivity of PdTe2, PdTe are well inherited by the candidate materials PdBi2Te5 and PdBi2Te4 with superconductivity transition temperature 0.57K and 3.11K, respectively. They further used their developed general program to construct the 2D slab BdG Hamiltonian of PdBi2Te5 and PdBi2Te4 film and calculate the superconducting spectrum and topological invariant with the introduction of Zeeman field on the surface. The results confirm the chiral topological superconducting phase. This work paves a new path and provides a tool to design and control the topological superconductor, gives the theoretical basis for the construction of the topological superconductor quantum devices.
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