标题： 拓扑半金属KAlGe与新型电子不稳定性 显示英文标题

标题： Topological Semimetal KAlGe with Novel Electronic Instability

摘要： 具有反-PbFCl结构的化合物表现出多种电子不稳定性以及有趣的物理性质。 NaAlSi和NaAlGe是类似的拓扑节线半金属，但它们具有不同的特性。 NaAlSi在6.8 K时是超导体，而NaAlGe是一个具有约100 K伪间隙的绝缘体。使用钾-铟助熔剂法，我们成功合成了KAlGe的新反-PbFCl化合物。 第一性原理电子结构计算表明，KAlGe与NaAlSi和NaAlGe是等电子的。 KAlGe在89 K时发生金属到金属的转变，并且在1.8 K以上没有超导性。低温相的载流子密度显著较低，且迁移率极高，类似于狄拉克电子系统。 此外，X射线衍射实验显示在相变过程中结构发生变化，破坏了四重对称性。 电子-声子相互作用可能是NaAlSi中超导性的原因，而激子电子-空穴相互作用被认为在KAlGe和可能的NaAlGe中起重要作用。 我们的发现表明，该化合物家族中存在迷人的物理现象。 显示英文摘要

摘要： Compounds with the anti-PbFCl structure exhibit a variety of electronic instabilities and intriguing physical properties. NaAlSi and NaAlGe are similar topological nodal-line semimetals, but they have distinct properties. NaAlSi is a superconductor at 6.8 K, whereas NaAlGe is an insulator with a pseudogap of approximately 100 K. Using the potassium-indium flux method, we succeeded in synthesizing a single crystal of KAlGe, a new anti-PbFCl compound. First principles electronic structure calculations reveal that KAlGe is isoelectronic with NaAlSi and NaAlGe. KAlGe undergoes a metal-to-metal transition at 89 K and exhibits no superconductivity above 1.8 K. The low temperature phase has significantly lower carrier density and extremely high mobility, similar to Dirac electron systems. Furthermore, X-ray diffraction experiments show a structural change that breaks the fourfold symmetry during the phase transition. Electron-phonon interactions may be responsible for superconductivity in NaAlSi, whereas excitonic electron-hole interactions are thought to play an important role in KAlGe and possibly NaAlGe. Our findings demonstrate that fascinating physics lies within the compound family.