Resonant second-order optical resonances in quantum magnets

Recently, laser control of materials has attracted much attention in various fields of condensed-matter physics. In 2016, Sato, Takayoshi, and Oka proposed an ultrafast way to add to a quantum magnet an effective Dzyaloshinskii-Moriya interaction dynamically. They confirmed their theoretical proposal by calculating the vector chirality to which the Dzyaloshinskii-Moriya interaction is coupled. They also pointed out numerically that there exists a resonance of the dynamically generated vector chirality when the frequency of the applied laser equals to the Zeeman energy of the quantum magnet. This resonance is interesting because the dynamical generation of the vector chirality is the second-order response to the laser but its resonance resembles another linear-response phenomenon to the laser, that is, electron spin resonance. Unfortunately, the resonant second-order response to the laser is yet to be understood. In this presentation, I discuss the origin of the resonant second-order resonance and exemplify it in quantum spin chain systems. I also show that the resonant second-order response can be found in quite a general situation of quantum magnets. For example, the magnetization also exhibits the same resonant second-order optical response.