Spin Excitations of 1D Cuprates Chains

High-temperature superconductivity in cuprates remains a captivating yet unresolved challenge in condensed matter physics. Recent photoemission studies have provided compelling evidence for a near-neighbor attractive interaction ($V$) in cuprate chains, hypothesized to play a critical role in enhancing pairing mechanisms. To explore this effect, we utilize the density matrix renormalization group (DMRG) method to calculate the dynamical spin structure factor, $S(q, \omega)$. Our analysis reveals a pronounced softening of the two-spinon continuum, particularly at high momentum, which we attribute to the renormalization of the superexchange interaction, $J$. Through comparisons with slave-boson mean-field theory, we identify this continuum softening as a potential hallmark of the attractive interaction ($V$). To validate this prediction, we propose resonant inelastic X-ray scattering (RIXS) experiments on thin-film cuprate samples. As a momentum-resolved technique for probing spin excitations, RIXS is exceptionally well-suited to detect the predicted softening of the two-spinon continuum, providing a direct and experimentally accessible pathway to verify the influence of attractive interactions in cuprate systems.