  Charge density waves (CDWs) underpin the electronic properties of many
complex materials. Near-equilibrium CDW order is linearly coupled to a
periodic, atomic-structural distortion, and the dynamics is understood in terms
of amplitude and phase modes. However, at the shortest timescales lattice and
charge order may become de-coupled, highlighting the electronic nature of this
many-body broken symmetry ground state. Using time and angle resolved
photoemission spectroscopy with sub-30-fs XUV pulses, we have mapped the time-
and momentum-dependent electronic structure in photo-stimulated 1T-TaS2, a
prototypical two-dimensional charge density wave compound. We find that CDW
order, observed as a splitting of the uppermost electronic bands at the
Brillouin zone boundary, melts well before relaxation of the underlying
structural distortion. Decoupled charge and lattice modulations challenge the
view of Fermi Surface nesting as a driving force for charge density wave
formation in 1T-TaS2.
