Fig. 1: Time-resolved measurement of the electronic order formation in presence of acoustic phonons.

a The laser pulse quenches the spin density wave (SDW), which is coupled to the periodic lattice distortion (PLD) (solid line on the left), and launches a pair of longitudinal acoustic phonons (atomic positions (blue spheres) and their wavevector (black arrows)). Subsequently, the SDW bandgap (schematic energy diagram on the right) reopens and the coupled SDW-PLD state reforms in presence of the phonons. b Typical time-resolved X-ray diffraction data of the coherent satellite-peak (purple dots) for an incident pump fluence of 2 mJ/cm². The data is fitted (purple solid line) with a damped harmonic oscillator in region II (blue shaded area), the fit is extrapolated to region I (red shaded area), and the extrapolated fit is subtracted from X-ray diffraction data. The residual is shown in orange and is proportional to the transient PLD amplitude coupled to the SDW through spin–lattice interaction. The inset shows typical diffraction data as measured on the two-dimensional detector for a single time delay. The coherent satellite-peak is in the center at Q₀₀₂– Q_L = 4.17 Å⁻¹, the image spans 0.14 Å⁻¹ horizontally, and the intensity drop towards the sides of the detector is due to the Ewald sphere intersecting the Bragg rod under an angle of 30 degrees.