标题： 节点拓扑在$d$波超导单层 FeSe 中 显示英文标题

标题： Nodal topology in $d$-wave superconducting monolayer FeSe

摘要： 无节点的$d$波态在SrTiO$_3$上的超导单层FeSe中可能是存在的。 无节点的现象令人惊讶，但已被证明是观察到的较小的带间自旋-轨道耦合的自然结果。 在这里，我们从拓扑学的角度考察当自旋-轨道耦合增加时，无节点态向有节点态的演化。 我们表明，这种演化强烈依赖于超导自由度的轨道组成。 特别是，存在两种$d$波解，我们称之为轨道平凡和轨道非平凡。 在两种情况下，节点都具有来自手征对称性的$\pm 2$拓扑绕数。 然而，正负电荷在动量空间中的分布对于这两种情况是不同的，导致它们在湮灭形成无节点超导体时的节点演化不同。 我们进一步表明，轨道平凡和轨道非平凡的有节点态在边缘表现出不同的安德烈夫平带谱。 显示英文摘要

摘要： A nodeless $d$-wave state is likely in superconducting monolayer FeSe on SrTiO$_3$. The lack of nodes is surprising but has been shown to be a natural consequence of the observed small interband spin-orbit coupling. Here we examine the evolution from a nodeless state to the nodal state as this spin-orbit coupling is increased from a topological perspective. We show that this evolution depends strongly on the orbital content of the superconducting degrees of freedom. In particular, there are two $d$-wave solutions, which we call orbitally trivial and orbitally nontrivial. In both cases, the nodes carry a $\pm 2$ topological winding number that originates from a chiral symmetry. However, the momentum space distribution of the positive and negative charges is different for the two cases, resulting in a different evolution of these nodes as they annihilate to form a nodeless superconductor. We further show that the orbitally trivial and orbitally nontrivial nodal states exhibit different Andreev flat band spectra at the edge.