Direct characterization of photo-induced lattice dynamics in BaFe2As2

TL;DR

This study uses time-resolved x-ray scattering to directly observe how ultrafast optical pulses induce coherent lattice oscillations in BaFe2As2, revealing potential for manipulating electronic properties via transient structural changes.

Contribution

It provides the first direct measurement of photo-induced lattice dynamics in BaFe2As2, demonstrating how small lattice distortions can significantly affect electronic and magnetic properties.

Findings

No ultrafast change in crystal symmetry observed.

Lattice oscillates via coherent excitation of an A1g mode.

Small lattice distortions can alter electronic and magnetic states.

Abstract

Ultrafast light pulses can modify the electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins, and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved x-ray scattering to measure the lattice dynamics of photo-excited BaFe2As2. Upon optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photo-induced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can generally be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands near the Fermi level.