Ultrafast broadband optical spectroscopy for quantifying subpicometric coherent atomic displacements in WTe2

This paper discusses how to quantify the amplitude of phononic atomic displacements by time resolved optical spectroscopy experiments. The approach is applied on WTe2, whose anisotropic transient reflectivity hosts signatures of coherent optical phonon modes at different quantities. Comparing the results of a model based on density functional theory with the experiment, the authors can determine the magnitude of the sub-picometric atomic displacements triggered by an impulsive excitation, without free tuning parameters. This approach can be extended to other materials to determine the atomic displacements with a few femtometers precision.