The origin of spontaneous electronic nematic ordering provides important information for understanding iron-based superconductors. Here, we analyze a scenario where the d_xy orbital strongly contributes to nematic ordering in FeSe. We show that the addition of d_xy nematicity to a pure d_xz/d_yz order provides a natural explanation for the unusual Fermi surface and correctly reproduces the strongly anisotropic momentum dependence of the superconducting gap. We predict a Lifshitz transition of an electron pocket mediated by temperature and sulfur doping, whose signatures we discuss by analysing available experimental data. We present the variation of momentum dependence of the superconducting gap upon suppression of nematicity. Our quantitatively accurate model yields the transition from tetragonal to nematic FeSe and the FeSe_1−xS_x series, and puts strong constraints on possible nematic mechanisms.

自发电子向列有序的起源为理解铁基超导体提供了重要的信息。在这里，我们分析了d _{x y}轨道对FeSe中向列有序性有很大贡献的情况。我们表明，将d _{x y}向列性加到纯d _{x z} / d _{y z上}序为不寻常的费米面提供了自然的解释，并正确地再现了超导间隙对强各向异性动量的依赖性。我们预测了由温度和硫掺杂介导的电子口袋的李夫希兹跃迁，我们将通过分析可用的实验数据来讨论其签名。我们提出了抑制向列性时超导间隙动量依赖性的变化。我们定量精确的模型产生了从四方向向列FeSe和FeSe _{1- x} S _x系列的过渡，并对可能的向列机制施加了严格的约束。