  It has been technically challenging to concurrently probe the electrons and
the lattices in materials during non-equilibrium processes, allowing their
correlations to be determined. Here, in a single set of ultrafast electron
diffraction patterns taken on the charge-density-wave (CDW) material 1T-TaSeTe,
we discover a temporal shift in the diffraction intensity measurements as a
function of scattering angle. With the help of dynamic models and theoretical
calculations, we show that the ultrafast electrons probe both the
valence-electron and lattice dynamic processes, resulting in the temporal shift
measurements. Our results demonstrate unambiguously that the CDW is not merely
a result of the periodic lattice deformation ever-present in 1T-TaSeTe but has
significant electronic origin. This method demonstrates a novel approach for
studying many quantum effects that arise from electron-lattice dephasing in
molecules and crystals for next-generation devices.
