Motivated by the recent discovery of a large anomalous Nernst effect in ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Ga}$, ${\mathrm{Fe}}_{3}X$ ($X$=Al, Ga) and ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$, we performed a first-principles study to clarify the origin of the enhancement of the transverse thermoelectric conductivity ${\alpha }_{ij}$ in these ferromagnets. The intrinsic contribution to ${\alpha }_{ij}$ can be understood in terms of the Berry curvature $\mathrm{\Omega }$ around the Fermi level, and $\mathrm{\Omega }$ is singularly large along nodal lines (which are gapless in the absence of the spin-orbit coupling) in the Brillouin zone. We find that not only the Weyl points but also stationary points in the energy dispersion of the nodal lines play a crucial role. The stationary points make sharp peaks in the density of states projected onto the nodal line, clearly identifying the characteristic Fermi energies at which ${\alpha }_{ij}$ is most dramatically enhanced. We also find that ${\alpha }_{ij}/T$ breaks the Mott relation and show a peculiar temperature dependence at these energies. The present results suggest that the stationary points will give us a useful guiding principle to design magnets showing a large anomalous Nernst effect.

中文翻译：

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节点线中固定点引起的横向热导率的提高

受最近发现的一个大异常能斯特效应的启发。 ${\mathrm{有限公司}}_2锰嘎$， ${铁}_{3}X$ （$X$= Al，Ga）和 ${\mathrm{有限公司}}_3{锡}_2{\mathrm{小号}}_2$，我们进行了第一性原理研究，以阐明横向热电导率增强的起源 ${\alpha }_{\mathrm{一世}Ĵ}$在这些铁磁体中。对……的内在贡献${\alpha }_{\mathrm{一世}Ĵ}$ 可以用贝里曲率来理解 $\mathrm{\Omega }$ 在费米水平附近，以及 $\mathrm{\Omega }$沿布里渊区的节点线（在没有自旋轨道耦合的情况下是无间隙的）奇异大。我们发现，节点线的能量扩散中不仅Weyl点而且静止点都起着至关重要的作用。固定点在投影到节点线上的状态密度中产生尖锐的峰值，从而清楚地识别出特征费米能。${\alpha }_{\mathrm{一世}Ĵ}$最显着地增强。我们还发现${\alpha }_{\mathrm{一世}Ĵ}/Ť$打破了莫特关系，并在这些能量下表现出独特的温度依赖性。目前的结果表明，这些固定点将为我们提供一个有用的指导原则，以设计显示出大反常能斯特效应的磁体。