Terahertz Field-Driven Nonlinear Magnonics in Antiferromagnets

Coherent excitations of magnetically ordered materials, referred to as spin waves and their quanta, magnons, have emerged as prominent candidates for interference-based signal processing technologies. Despite growing interest in manipulating magnonic states beyond thermodynamic equilibrium, elucidating and inducing coherent couplings between distinct magnon modes remains a formidable challenge. By developing and employing a novel two-dimensional (2D) terahertz (THz) polarimetry technique facilitated by single-shot detection, we successfully uncover correlated magnonic states at the sum and difference frequencies of the two modes, as well as a second-order magnon upconversion response. These findings not only expand the domain of nonlinear magnonics by incorporating antiferromagnets but also lay the groundwork for further advancements in the ultrafast control of magnetism.