Since their discovery in 1986, copper-oxide high-temperature superconductors stimulated a wide interest of the scientific community, because of their property to sustain the superconducting state at considerably higher temperature than conventional superconductors. After 30 years of intense studies, both theoretical and experimental, a number of questions remain still elusive. In particular, the dichotomy in the nature of the quasiparticles across the Fermi surface of the material, that has been speculated as being the origin of several unconventional properties of these materials, has never been directly measured.
Here we report on time- and angle-resolved photoelectron spectroscopy (TR-ARPES) studies on the Bi2Sr2CaCu2O8 (Bi2212) compound, performed with a VUV probe. With this approach we are able to overcome the limits of TR-ARPES setups operated with ~6 eV photon energy and probe both the nodal and the antinodal states, allowing to characterize the nature of excitations over the entire Brillouin zone of the compound. To this aim we developed a novel source of ultrashort VUV photons, obtained as the sixth harmonics at 8.55 eV of the IR output of a parametric amplifier. This surce provides a large flux thanks to the possibility to produce third-harmonic-generation (THG) in Xenon in the negative-dispersion regime. Futhermore, we report on the first characterization of a novel high-harmonic-generation (HHG) setup operating at high repetition-rate (>50 kHz), that will allow us to further widen the range of momenta and kinetic energies that can be probed with TR-ARPES. These preliminary results are compared with numerical simulations on the phase-matching conditions in Argon gas. Thanks to the developments we pursued in advancing the ultrafast sources for TR-ARPES, we have been able to considerably widen the range of accesisble energy-momentum space, which is particularly relevant for the case of correlated materials with strongly anisotropic Fermi surfaces, paving the way to the study of the previously unaccessible antinodal state. This novel possibility will provide key information for a deeper understanding of the nature of antinodal quasiparticle in copper oxides.