We investigate the spin dynamics of the cuprate ladder ${\mathrm{Sr}}_{2.5}{\mathrm{Ca}}_{11.5}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ to elucidate the behavior of its intrinsically doped holes. By combining high-resolution inelastic neutron spectroscopy with density-matrix renormalization group calculations, we obtain a detailed and quantitative description of its collective magnetic excitations within a single-band framework. Remarkably, we observe an absence of magnetic signatures associated with unpaired charges, suggesting that the doped holes form strongly bound, localized Cooper pairs. Indeed, while the standard single-band Hubbard model fails to reproduce the observed excitation spectrum, a minimal extension incorporating a strong attractive nearest-neighbor interaction quantitatively accounts for the experimental results. Our findings underscore the necessity of including interactions beyond conventional magnetic mechanisms in driving charge pairing when the system is modeled using the single-band Hubbard model. Given the close correspondence between ladder systems and two-dimensional cuprates, these results may have important implications for pairing phenomena in square-lattice cuprate materials.

Close

PrevNext

View figure in article

• Density matrix renormalization group
• Localization
• Superconductivity
• Inelastic neutron scattering