Photoinduced structural dynamics of multiferroic TbMnO$_3$

TL;DR

This study uses time-resolved x-ray diffraction to observe how photoexcitation causes rapid, subtle structural changes in multiferroic TbMnO$_3$, linking these to magnetic order dynamics.

Contribution

It provides the first direct measurement of ultrafast lattice responses in TbMnO$_3$ following optical excitation, revealing a bottleneck in energy transfer and its relation to demagnetization.

Findings

Transient tensile strain of 0.02% within 20-30 ps

Strain magnitude lower than predicted by heating models

Correlation between structural dynamics and magnetic order disruption

Abstract

We use time-resolved hard x-ray diffraction to investigate the structural dynamics of the multiferroic insulator TbMnO$_3$ in the low temperature antiferromagnetic and ferroelectrically ordered phase. The lattice response following photoexcitation at 1.55 eV is detected by measuring the (0 2 4) and (1 3 -5) Bragg reflections. A 0.02% tensile strain, normal to the surface, is seen to arise within 20 - 30 ps. The magnitude of this transient strain is over an order of magnitude lower than that predicted from laser-induced heating, which we attribute to a bottleneck in the energy transfer between the electronic and lattice subsystems. The timescale for the transient expansion is consistent with that of previously reported demagnetization dynamics. We discuss a possible relationship between structural and demagnetization dynamics in TbMnO$_3$, in which photoinduced atomic motion modulates the exchange interaction, leading to a destruction of the magnetic order in the system.