npj: 刘锋教授发现的高Tc超导体秘密—Dirac节点线费米子

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超导和拓扑态是自然界中最迷人的量子现象之一。将这两种态在固体材料中纠缠成拓扑超导态（如Majorana费米子）将产生更奇特的量子现象。具有拓扑保护的无带隙表面/边缘态特征，存在于体材超导带隙中，包含了Majorana费米子。不幸的是，所有目前已知的拓扑超导体转变温度都非常低，限制了Majorana费米子的实验测量。

来自由美国犹他大学和中国量子物质协同创新中心的刘锋教授团队，使用第一性原理计算和模型分析，揭示了这种Dirac节点线态。最重要的是，他们用传统的s波超导带隙实现了拓扑超导相，用MgB₂薄膜的拓扑边缘模式证明了手征边缘状态。他们的发现为在前所未有的高温下研究拓扑超导相提供了一个令人兴奋的机会，并可能为构建新型量子和自旋电子器件，提供有前途的材料平台。有可能在高温下实现对Majorana费米子的实验测量，将激发未来更广泛的超导材料拓扑相（如蜂窝状层状晶格结构）研究。

该文近期发表于npj Computational Materials 5: 57 (2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

Topological superconducting phase in high-Tc superconductor MgB₂ with Dirac–nodal-line fermions 

Kyung-Hwan Jin, Huaqing Huang, Jia-Wei Mei, Zheng Liu, Lih-King Lim & Feng Liu 

Topological superconductors are an intriguing and elusive quantum phase, characterized by topologically protected gapless surface/edge states residing in a bulk superconducting gap, which hosts Majorana fermions. Unfortunately, all currently known topological superconductors have a very low transition temperature, limiting experimental measurements of Majorana fermions. Here we discover the existence of a topological Dirac–nodal-line state in a well-known conventional high-temperature superconductor, MgB₂. First-principles calculations show that the Dirac–nodal-line structure exhibits a unique one-dimensional dispersive Dirac–nodal line, protected by both spatial-inversion and time-reversal symmetry, which connects the electron and hole Dirac states. Most importantly, we show that the topological superconducting phase can be realized with a conventional s-wave superconducting gap, evidenced by the topological edge mode of the MgB₂ thin films showing chiral edge states. Our discovery may enable the experimental measurement of Majorana fermions at high temperature.

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