On demand laser-induced frequency tuning of coherent magnons in a nanometer-thick magnet at room temperature.

The collective vibrational and magnetic response of a solid to external stimuli is encoded in the dispersion relations of phonons and magnons, respectively. Recently, the coherent drive and nonlinear manipulation of collective lattice and magnetic excitations via laser pulses has been explored, as a route to control the non-equilibrium properties of quantum materials. Device concepts that leverage coupled multiphysical dynamics must exhibit laser-induced frequency tunability controllable through external parameters. Although previous works have shown that optically driven excitations in the midinfrared can manipulate magnon frequencies, inducing deterministic red- or blue-shifts of the magnon frequency in the same material is still elusive. Here we demonstrate this concept in a nanometer-thick magnet at room temperature. Visible light pulses in combination with an external magnetic field (<200 mT) can either raise or lower the magnon frequency by up to 40% of its original value. This effect results from the interplay of the optical excitation, magnetic anisotropy and external magnetic field. Our results show how an efficient manipulation of magnons can be achieved by light and provide perspectives for the realization of logic devices optically reconfigurable on the nanosecond timescale.