Understanding spin excitations in cuprates by combining RIXS and numerical simulation

The topic of spin excitations is central to the field of unconventional superconductivity. For the high-temperature cuprate superconductors, resonant inelastic X-ray scattering (RIXS) has emerged as a leading technique for probing spin excitations across much of the Brillouin zone. Here we present high-resolution RIXS spectra on two compounds, La_2-xSr_xCuO₄ (LSCO) and (Bi,Pb)₂(Sr,La)₂CuO_6+x (Bi2201), studying in detail the doping dependence of the spin excitations' dispersion, damping, and intensity in the underdoped region of LSCO and across the entire phase diagram of Bi2201. We show that the excitations' dispersion and redistribution of spectral weight upon doping are captured by the three-orbital Hubbard model, which we numerically simulate via determinantal quantum Monte Carlo. We further discuss the connection between charge transfer energy and compound-specific properties of spin excitations. The consistency between our model calculations and experimental data support a unified picture of spin excitations in the cuprates.