Terahertz Control of Linear and Nonlinear Magno-Phononics

TL;DR

This paper demonstrates the coherent control of magnon-polarons in a van der Waals antiferromagnet using terahertz pulses, revealing both linear and nonlinear excitation regimes and enabling ultrafast manipulation of magnetic properties.

Contribution

It uncovers the linear excitation channel of magnon-polarons via strong magnon-phonon coupling, previously considered forbidden, and demonstrates control over their amplitude through terahertz field tuning.

Findings

Achieved both linear and quadratic excitation of magnon-polarons

Controlled magnon-polaron oscillations by tuning terahertz field strength and polarization

Broken crystallographic symmetry through interference effects

Abstract

Coherent manipulation of magnetism through the lattice provides unprecedented opportunities for controlling spintronic functionalities on the ultrafast timescale. Such nonthermal control conventionally involves nonlinear excitation of Raman-active phonons which are coupled to the magnetic order. Linear excitation, in contrast, holds potential for more efficient and selective modulation of magnetic properties. However, the linear channel remains uncharted, since it is conventionally considered forbidden in inversion symmetric quantum materials. Here, we harness strong coupling between magnons and Raman-active phonons to achieve both linear and quadratic excitation regimes of magnon-polarons, magnon-phonon hybrid quasiparticles. We demonstrate this by driving magnon-polarons with an intense terahertz pulse in the van der Waals antiferromagnet $\mathrm{FePS_3}$. Such excitation behavior enables a unique way to coherently control the amplitude of magnon-polaron oscillations by tuning the terahertz field strength and its polarization. The polarimetry of the resulting coherent oscillation amplitude breaks the crystallographic $C_2$ symmetry due to strong interference between different excitation channels. Our findings unlock a wide range of possibilities to manipulate material properties, including modulation of exchange interactions by phonon-Floquet engineering.