UNFOLDING THE ULTRAFAST INTERPLAY BETWEEN DELOCALIZED WAVEFUNCTIONS AND LOCALIZED ELECTRONIC INTERACTIONS IN QUANTUM CORRELATED MATERIALS

The complex phase diagram of strongly correlated materials is regulated by the delicate interplay between the low-energy electronic excitations and those involving higher energy scales. Here we combine time-resolved optical spectroscopy, conventional laser photoemission (tr-ARPES) and XUV-laser photoemission (XUV-ARPES) to investigate, with an out-of-equilibrium approach, the high-energy electron dynamics in two families of superconducting copper oxides: the single-layer Bi2Sr2-xLaxCuO6+d (Bi2201) and double-layer Bi2Sr2Ca0.92Y0.08Cu2O8+d (Bi2212). We focused on the pump induced modification of the charge-transfer (CT) transition at >2 eV, that strongly reflects the correlation degree of the electronic wavefunction. We observe a qualitative change of the dynamics of the CT transition at T=300 K and hole doping p_cr=0.17+-0.02. We argue that the observed change at p_cr is intimately connected to the quantum critical point at T=0, from which different charge and spin ordering tendencies emerge. Furthermore, time-resolved XUV angle-resolved-photoemission experiments allowed us to track the transient occupation of both the conduction and the oxygen bands during the relaxation dynamics. Our results unveiled the different nature (bonding, non-bonding) of the oxygen bands at 1.5 eV binding energy. This is reflected in a strong bottleneck in the relaxation of the holes photoexcited in the O-2p-pi band at (pi,pi) which is non-bonding with the 3dx^2-y^2 Cu states.These results challenge the state-of-the-art models that describe the relaxation dynamics in copper oxides.