  In Peierls-distorted materials, photoexcitation leads to a strongly coupled
transient response between structural and electronic degrees of freedom, always
measured independently of each other. Here we use transient reflectivity in the
extreme ultraviolet to quantify both responses in photoexcited bismuth in a
single measurement. With the help of first-principles calculations based on
density-functional theory (DFT) and time-dependent DFT, the real-space atomic
motion and the temperature of both electrons and holes as a function of time
are captured simultaneously, retrieving an anticorrelation between lattice
expansion and carrier temperature. The results reveal a coherent,
bi-directional energy exchange between carriers and phonons, which is a
dynamical counterpart of the static Peierls-Jones distortion, providing
first-time validation of previous theoretical predictions.
