Optical pump-induced strain waves in kagome metals

Our previous measurements in ID09 revealed an extremely slow lattice relaxations (despite a good metallic character) and a long-standing coherent intensity oscillations on the Gd-compound. At first glance, these oscillations could be the strain waves generated due to the optical pumping in the material. However, considering the high magnetic transition temperature (TN= 425 K) and high-energy magnons present, we cannot rule out the magnetic degree of freedom, either. Regardless of the origin, these oscillations seem to couple to the slow lattice relaxation and therefore, key to understand this unusual behavior, which we seek to identify here.