Special AEP Seminar by Alex von Hoegen (MIT)

Description

Alex von Hoegen
Postdoctoral Fellow at MIT

Non-thermal engineering of solid-state systems via THz driven collective modes
Mode-selective excitation of collective modes has emerged as a versatile tool to investigate and control the interplay between microscopic degrees of freedom. Driven to large amplitudes, these modes access a non-linear regime and can provoke drastic change of the material properties. In this talk, I will address the nonlinear dynamics of strongly driven collective modes and demonstrate how to use them to dynamically material properties. We used time-resolved second harmonic generation (tr-SHG) to directly measure the large amplitude oscillations of a THz driven infrared-active mode in the ferroelectric material LiNbO3. The amplitude and phase sensitive detection of the lattice dynamics allowed us to reconstruct the lattice potential energy. We applied this excitation scheme to the layered antiferromagnet FePS3. In this compound, our THz excitation launches spin and lattice dynamics, giving rise to coherent magnons and phonons with characteristic symmetries, temperature dependences and excitation field scaling. Besides these coherent dynamics, we also observe the emergence of slow dynamics close to the Neel temperature TN = 118 K, concomitant with the appearance of a long-lived circular dichroism (CD). This is evidence for a finite out-of-plane magnetization inside the sample. These findings demonstrate how the magnetic state in a 2D van der Waals magnets can be efficiently manipulated through strong spin-lattice coupling.

Hosted by: Ankit Disa