The project has been managed on different fronts, which represent the various experimental tools:
a) One pre-requisite is the description of the optical absorption spectrum, which calls for the use of steady-state and time-resolved near- to far-UV spectroscopic tools. These have been used to characterise the optical absorption spectrum of anatase and rutile TiO2, which has been analysed and published. In particular, we have unravelled the existence for the first time of 2-dimensional excitons in the 3-dimensional lattice of a solid, namely anatase TiO2. We also carried out the characterization of ZnO and spinel cobalt oxide, and the results are being written up at present.
b) As an extension of the above studies, we have characterised the charge carrier dynamics and phonon dynamics in anatase TiO2. Several new results have been obtained, namely the electron cooling time has been determined for the first time, giant couplings between excitons and acoustic phonons have been discovered and hold promise of using anatase TiO2 as a mechanical sensor with all-optical read-out. We have also demonstrated how the excitonic resonance of the material can be used as a probe of electron injection and its time scale in photovoltaics and results were obtained for anatase TiO2 and for ZnO.
c) We have implemented a time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiment and have carried out test studies on different materials (chiral tellurium, 2D black phosphorus, on semi-metals and on inorganic perovskite crystals). For all these systems, the steady-state and ultrafast characterization oof the electronic structure and the charge carriers has been carried.
d) Optical ultrafast spectroscopic measurements have been carried out on spinel cobalt oxide and the results are being analysed. These studies were a pre-requisite for ultrafast X-ray emission spectroscopy experiments, which were carried out at the European X-ray Free electron laser (XFEL, Hamburg). Furthermore, extreme Ultraviolet(EUV) Transient Grating experiments were successfully carried out at the FERMI XFEL in Trieste (Italy). These various results are now being analysed and will soon be written up for publication.
e) By a combination of picosecond X-ray absorption and resonant inelastic X-ray scattering (RIXS), we have observed for the first time the trapping of holes in a TMO. The results have been published and another X-ray spectroscopy study with femtosecond resolution will soon be submitted for publication.
f) The femtosecond hard X-ray RIXS experiment has been commissioned and the first results on an Iridate compound have been obtained. The analysis also shows a time-resolved signal. Furthermore, a set of ultrafast optical pump-probe studies have been carried out which will help understand the RIXS studies.
