TMDC-based topological nanospaser: single and double threshold behavior

We theoretically study a topological nanospaser, which consists of a silver nanospheroid and MoS$_2$ monolayer ake of a circular shape. The metal nanospheroid acts as a plasmonic nanoresonator that supports two rotating modes, which are coupled to the corresponding valleys of MoS$_2$. We apply external circularly polarized light that selectively pumps only one of the valleys of MoS$_2$. The generated spaser dynamics strongly depends on the size (radius) of the MoS$_2$ nanoflake. For small radius, the system has only one spasing regime when only chirally-matched plasmon mode is generated, while at larger size of MoS$_2$, depending on the pump intensity, there are two regimes. In one regime, only the chirally-matched plasmon mode is generated, while in the other regime both chirally-matched and chirally-mismatched modes exist. Different regimes of spaser operation have also opposite handedness of the far-field radiated of the spaser system. Such topological nanospaser has potential applications in different areas of infrared spectroscopy, sensing, probing, and biomedical treatment.