Unravelling the Nature of the Spin Excitations Disentangled from the Charge Contributions in a Doped Cuprate Superconductor

The nature of the spin excitations in superconducting cuprates is a key question toward a unified understanding of the cuprate physics from long-range antiferromagnetism to superconductivity. The intense spin excitations up to the over-doped regime revealed by resonant inelastic X-ray scattering bring new insights as well as problems—like understanding their persistence or their relation to the collective excitations in ordered magnets (magnons). Here, we study the evolution of the spin excitations upon hole-doping the superconducting cuprate Bi2Sr2CaCu2O8+δ by disentangling the spin from the charge excitations in the experimental cross section. We compare our experimental results against density matrix renormalization group calculations for a t-J-like model on a square lattice. Our results unambiguously confirm the persistence of the spin excitations, which are closely connected to the persistence of short-range magnetic correlations up to high doping. This suggests that the spin excitations in hole-doped cuprates are related to magnons—albeit short-ranged.The experiments were performed at the ADRESS beamline of the Swiss Light Source at the Paul Scherrer Institut (PSI). The experimental work at PSI is supported by the Swiss National Science Foundation through project no. 200021_178867, and the Sinergia network Mott Physics Beyond the Heisenberg Model (MPBH) (SNSF Research Grants CRSII2 160765/1 and CRSII2 141962). The theoretical work is supported by the Narodowe Centrum Nauki (NCN, Poland) under Project Nos. 2016/22/E/ST3/00560 (C.E.A. and K.W.), 2021/40/C/ST3/00177 (C.E.A.) and 2016/23/B/ST3/00839 (K.W.). We acknowledge sup- port by the Interdisciplinary Centre for Mathematical and Computational Modeling (ICM), University of Warsaw (UW), within grant no G81-4. S.N. acknowledges support from SFB 1143 project A05 (project-id 247310070) of the Deutsche Forschungsgemeinschaft. T.C.A. acknowledges funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 701647 (PSI-FELLOW-II-3i program)