Triplons, triplon pairs, and dynamical symmetries in laser-driven Shastry-Sutherland magnets

In frustrated magnets, a variety of novel phenomena arise due to their peculiar magnetic states, whose excitations usually reside in the GHz to THz range. Intense THz lasers, therefore, lead to examining nonlinear optical effects in such magnets. Employing an unbiased numerical method, we calculate the laser-pulse driven harmonic spectra of the Shastry-Sutherland magnets, which are well known as the model of a quantum frustrated magnet $\mathrm{SrCu}{}_{2}$($\mathrm{BO}{}_{3}$)${}_{2}$. As a result, nonlinear responses of triplons and a two-triplon bound state are numerically shown to emerge through the Zeeman or magnetoelectric couplings between the laser and the electron spin. Furthermore, the dynamical symmetries and selection rules of harmonic spectra for the Shastry-Sutherland model realized in $\mathrm{SrCu}{}_{2}$($\mathrm{BO}{}_{3}$)${}_{2}$, are derived. The selection rules tell us that one can obtain information on magnetic anisotropy and symmetry from the spectra by manipulating external fields or two-color lasers. Our results indicate that laser-driven harmonic spectra are useful as a probe of less-detectable quantum many-body states in frustrated magnets.