Spin-orbit coupling induced ultrahigh-harmonic generation from magnetic dynamics

Abstract

The generation of a nonlinear high-frequency response in solids from powerful optical pumps has gained momentum over the past decade. High-harmonic generation (HHG) in solids can be obtained from strong-field laser excitation, usually restricted to optical frequencies and limited both in amplitude and in harmonic order. Here, we demonstrate that high-harmonic emission can be achieved by exploiting conventional spin pumping, without the need for optical excitation. Considering a noncentrosymmetric (ferro- or antiferro-)magnet excited at a frequency ω, we demonstrate the emergence of HHG in two main regimes: (i) In the perturbative regime, where a weak spin-orbit interaction is considered, the carrier pumping features a number of harmonics with a cutoff order nmax<10. (ii) When the spin-orbit coupling strength is close to, or higher than, the s-d exchange energy, a strongly nonlinear regime resulting from resonantlike spin-flip scattering occurs leading to the emission of a large number of harmonics. This is in sharp contrast to conventional pumping, where the corresponding time-dependent currents simply oscillate with the frequency of the magnetic drive ω. Our proposal enables the enhancement of both spin and charge dynamics by orders of magnitude. This effect could be used to trigger high-frequency emission deep in the terahertz regime.