Charge and Spin Excitations in Zn-Doped Cuprate Superconductors probed by Resonant X-ray Scattering

In this thesis I investigate how minimal ionic disorder reshapes collective excitations in the cuprate high-critical temperature YBa2Cu3O7−δ (YBCO). Replacing a small fraction of Cu with non-magnetic Zn suppresses superconductivity (SC) while leaving the crystal structure essentially unchanged, providing a clean way to test whether charge order and spin excitations are spectators or active ingredients of pairing. I follow a two-step resonant X-ray scattering approach. First, energy-integrated RXS (EI-RXS) at BESSY II maps charge density wave (CDW) correlations versus doping. From the CDW intensity, correlation strength and onset temperature. I reconstructed a CDW “dome” and compared it with pristine YBCO. Despite the reduced superconducting dome and lower Tc, CDW correlations are also weaker and persist over the same doping range, peaking at p~0.12 where Zn-doped samples are already non-superconducting. Second, I analyze RIXS spectra from the AF parent compound to the strongly overdoped regime and fit pristine and Zn-doped datasets consistently to compare magnon/paramagnon dispersions. Within experimental sensitivity, the paramagnon energies are unchanged by Zn, allowing extraction of the magnetic exchange scale J and demonstrating robust short-range spin dynamics even when SC is suppressed. Overall, my results indicate that CDW correlations are not sufficient to sustain SC and that robust spin excitations alone are unlikely to fully account for cuprate pairing.