We theoretically study first- and second-order optical responses in a transition-metal dichalcogenide monolayer with distinct trivial, nodal, and time-reversal invariant topological superconducting (TRITOPS) phases. We show that the second-order dc response, also known as the photogalvanic response, contains signatures for differentiating these phases while the first-order optical response does not. We find that the high-frequency photogalvanic response is insensitive to the phase of the system, while the low-frequency response exhibits features distinguishing the three phases. At zero doping, corresponding to an electron filling in which the Fermi level lies at nodal points, there are opposite sign zero-frequency divergences in the response when approaching the nodal phase boundaries from the trivial and the TRITOPS phases. In the trivial phase, both the high-frequency and low-frequency response of the system are negative, but in the TRITOPS phase the low-frequency response becomes positive while the high-frequency response remains negative. Furthermore, since phase transitions are controlled by the Rashba spin-orbit coupling and the ratio of intraorbital and interorbital paring amplitudes, our results not only help distinguish the phases but they can also provide an estimate of the pairing amplitudes based on the photogalvanic response of the system.

中文翻译：

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多轨道拓扑超导体中的非线性光学响应

我们从理论上研究了具有不同平凡相、节点相和时间反转不变拓扑超导（TRITOPS）相的过渡金属二硫族化物单层中的一阶和二阶光学响应。我们表明，二阶直流响应（也称为光电响应）包含区分这些相位的特征，而一阶光学响应则不包含。我们发现高频光电响应对系统的相位不敏感，而低频响应则表现出区分三相的特征。在零掺杂时，对应于费米能级位于节点的电子填充，当从平凡相和TRITOPS相接近节点相边界时，响应中存在相反符号的零频率发散。在tritops阶段，系统的高频响应和低频响应均为负值，但在TRITOPS阶段，低频响应变为正值，而高频响应保持为负值。此外，由于相变是由 Rashba 自旋轨道耦合以及轨道内和轨道间配对幅度之比控制的，因此我们的结果不仅有助于区分相位，而且还可以根据光电流响应提供配对幅度的估计。系统。