Doping dependence of 2-spinon excitations in the doped 1D cuprate Ba 2 CuO 3+ delta
The study used Cu L3-edge RIXS to examine 2-spinon excitations in doped Ba2CuO3+δ to test if a simple Hubbard model is sufficient. Findings showed that near the Brillouin zone boundary, these excitations are much softer than predicted by the simple model. This discrepancy suggests an additional attractive potential between holes, supporting its role in high-$T_c$ superconductivity.