Resonant optical control of the structural distortions that drive ultrafast demagnetization in Cr$_2$O$_3$

TL;DR

This study demonstrates how ultrashort visible light pulses with specific polarization and energy can control the structural and magnetic dynamics in Cr$_2$O$_3$, enabling fast manipulation of its antiferromagnetic state.

Contribution

It reveals that different photoexcited states couple to specific phonon modes, allowing selective control of demagnetization dynamics in Cr$_2$O$_3$ using polarization and photon energy.

Findings

SHG signal is sensitive to lattice displacements and magnetic order changes.

Different excitation energies lead to distinct demagnetization pathways.

Control over demagnetization timescale is achieved through selective photoexcitation.

Abstract

We study how the color and polarization of ultrashort pulses of visible light can be used to control the demagnetization processes of the antiferromagnetic insulator Cr$_2$O$_3$. We utilize time-resolved second harmonic generation (SHG) to probe how changes in the magnetic and structural state evolve in time. We show that, varying the pump photon-energy to excite either localized transitions within the Cr or charge transfer states, leads to markedly different dynamics. Through a full polarization analysis of the SHG signal, symmetry considerations and density functional theory calculations, we show that, in the non-equilibrium state, SHG is sensitive to {\em both} lattice displacements and changes to the magnetic order, which allows us to conclude that different excited states couple to phonon modes of different symmetries. Furthermore, the spin-scattering rate depends on the induced distortion, enabling us to control the timescale for the demagnetization process. Our results suggest that selective photoexcitation of antiferromagnetic insulators allows fast and efficient manipulation of their magnetic state.