High-harmonic generation in quantum spin systems

High-harmonic generation (HHG), a nonlinear response to strong laser driving, has been studied extensively for electron systems excited by the laser $e\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c$ field. Here, the authors extend this concept to quantum spin systems driven by the laser $m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c$ field and propose a novel probe for the magnetic structure. The radiation emitted by time-dependent magnetic dipoles exhibits HHG spectra with plateau structures, whose cutoff energies correspond to the energy scale of the magnetic excitations. This maps out an exciting route for the implementation of HHG in solids. In addition, the similarities and the differences between HHG in electron and spin systems are also discussed.