Dynamical Control of Antiferromagnetic Spin-Wave Spectrum via Light-Driven Electronic Excitation

Antiferromagnetic (AFM) materials feature intrinsic terahertz (THz) spin dynamics, rendering them ideal candidates for future ultrafast and low-energy magnonic and spintronic devices, aimed to use spin instead of conventional charge degrees of freedom. Manipulating the spin-wave spectrum is the most direct way to control the AFM’s response times and thus device operational rates. However, efficiently achieving such control is challenging, as it necessitates fast as well as long-lasting access to the strength of microscopic interactions (e.g. exchange and/or magnetic anisotropy) governing the AFM state. Here, we discuss how it can be efficiently done with the help of ultrashort pulses of light, by pumping electronic transitions in the prototypical charge-transfer AFM insulator DyFeO₃. In turn, this leads to the appearance of thermally inaccessible, in-gap spin-wave states. Using numerical simulations, we show that the emergence of such states is due to a long-lasting action of the electronic excitation on the magnetic interactions which shape the spin-wave spectrum. The modification leads to the formation, within the equilibrium magnon gap, of a nearly-flat split-off band, spatially localized near the sample surface. Our research not only paves the way for antiferromagnetic magnonics and dynamic control of AFM states, but also unveils new avenues for exploring the exotic nonequilibrium physics in AFMs, as well as the interplay between charge and spin degrees of freedom, situated at vastly different characteristic energy scales.