  A new approach for few-femtosecond time-resolved photoelectron spectroscopy
in condensed matter that balances the combined needs for both temporal and
energy resolution is demonstrated. Here, the method is designed to investigate
a prototypical Mott insulator, tantalum disulphide (1T-TaS2), which transforms
from its charge-density-wave ordered Mott insulating state to a conducting
state in a matter of femtoseconds. The signature to be observed through the
phase transition is a charge-density-wave induced splitting of the Ta 4f
core-levels, which can be resolved with sub-eV spectral resolution. Combining
this spectral resolution with few-femtosecond time resolution enables the
collapse of the charge ordered Mott state to be clocked. Precise knowledge of
the sub-20-femtosecond dynamics will provide new insight into the physical
mechanism behind the collapse and may reveal Mott physics on the timescale of
electronic hopping.
