Laser-induced dynamics of the magnon spectrum probed by double-pump THz spectroscopy

Ultrafast laser excitation has been shown to change the ratio between the constants of the Dzyaloshinskii–Moriya interaction (D) and isotropic exchange interaction (J) in antiferromagnets. Here, we reveal the dynamics of this laser-induced change by investigating the transient evolution of the magnon frequency of the quasi-antiferromagnetic mode in ErFeO3 using double-pump THz emission spectroscopy. We show that the resonance frequency, and hence the JD product, changes upon laser excitation on a timescale faster than the ps resolution of our experiment and that this change remains constant for at least 55 ps. It is argued that the laser-induced changes in the frequency are mainly due to changes in D and stem from the excitation of real electronic states.