Fulvio Parmigiani

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Cuprate superconductors evolve from Mott-insulating behavior at half-filling to itinerant correlated states upon hole doping. In this crossover regime, a central role is played by the Zhang–Rice Singlet (ZRS)—a bound state of an O-2p hole and a Cu-3d electron—that acts as a building block of quasiparticle transport and spin correlations.
In this talk, we report time-resolved X-ray absorption spectroscopy (tr-XAS) measurements at the oxygen K-edge on overdoped Bi₂Sr₂CaCu₂O₈₊δ (Bi2212), performed at the FLASH Free Electron Laser (DESY). Our data reveal that ZRS states in the overdoped regime hybridize into a coherent band, enabling delocalized hole transport. Upon ultrafast near-infrared (NIR) excitation, we observe a prompt modulation of the ZRS spectral weight, reflecting rapid charge redistribution between Cu–O planes and the out-of-plane reservoir layers.
Critically, this ZRS dynamics is intimately linked to many-body renormalizations observed in the low-energy electrodynamic response. We explore the transient behavior of the ∼70 meV dispersion kink seen in ARPES—associated with coupling to bosonic modes—and ∼40 meV optical features that echo magnetic resonance modes observed in neutron scattering. These signatures point toward a dynamical entanglement between ZRS charge fluctuations and spin excitations, with NIR pulses triggering a cascade of collective response across orbital and magnetic channels.
This combined approach demonstrates how ultrafast X-ray spectroscopy, optical conductivity, and momentum-resolved probes can be synthesized to access the coupled landscape of charge, spin, and transport dynamics in high-TcT_cTc cuprates—paving the way toward selective control of correlated states using soft X-ray excitation.

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University of Trieste and Elettra Sincrotrone Trieste (Italy)

Contact: Paul Van Loosdrecht