Electrons can be pulled from metallic surfaces using photon energies smaller than the work function if the light field is strong enough. In this work, we use the near-field enhancement at the apex of a nanotip to reach fields > 40 GV/m, tilting the potential such that electrons can tunnel directly from the Fermi surface. We show large bunch charges in excess of 106 electrons, which are accelerated from rest to kilo-electronVolts in about 10 fs.

Relativistically moving dielectric perturbations can be used to manipulate light in new and exciting ways beyond the capabilities of traditional nonlinear optics.

The complex coupling between charge carriers and phonons is responsible for diverse phenomena in condensed matter. We apply ultrafast electron diffuse scattering to unravel electron-phonon coupling phenomena in 1T-TiSe2 in both momentum and time to unravel the underlying mechanisms driving the phonon softening that is associated with the charge density wave transition at lower temperatures. 

Interactions between the lattice and charge carriers can drive the formation of phases and ordering phenomena that give rise to conventional superconductivity, insulator-to-metal transitions, and charge-density waves. These couplings also play a determining role in properties that include electrical and thermal conductivity. Ultrafast electron diffuse scattering (UEDS) has recently become a viable laboratory-scale tool to track energy flow into and within the lattice system across the entire Brillouin zone, and to separate interactions in the time domain. Here, we present a detailed quantitative framework for the interpretation of UEDS signals, ultimately extracting the phonon-mode occupancies across the entire Brillouin zone.