Spin-orbit coupling induced ultrahigh-harmonic generation from magnetic dynamics
Ousmane Ly, Aurélien Manchon
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 $\ensuremath{\omega}$, 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 ${n}_{\mathrm{max}}<10$. (ii) When the spin-orbit coupling strength is close to, or higher than, the $s\text{\ensuremath{-}}d$ 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 $\ensuremath{\omega}$. 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.