Cuprate Ladder: Structure, Dynamics, and Superconductivity Mechanism

Quasi-one-dimensional cuprate ladders exhibit a rich interplay among lattice, charge, and spin degrees of freedom, which may underlie their unconventional superconductivity under pressure. We investigated the structure, phonon, and spin dynamics of the Sr_14-xCa_xCu₂₄O₄₁ (SCCO) ladder system using single-crystal neutron diffraction and inelastic neutron scattering. Distinct diffraction patterns emerge upon Ca doping, revealing an enhanced chain correlation length and stronger coupling between the chain and ladder sublattices. Unusual high-energy vibrational and magnetic responses point to localized phonon modes and orbital inhomogeneity closely associated with hole crystallization on the ladder.

Building on our structural, phonon, and spin dynamic studies, together with previous reports, we propose a new framework for understanding the superconductivity mechanism in SCCO. While magnetic excitations are often considered the dominant pairing channel in unconventional superconductors, our results highlight the critical role of low-frequency phonons, providing new insight into how structural incommensurability mediates charge correlations in low-dimensional cuprates. These findings establish an experimental foundation for understanding the superconducting mechanism in correlated quasi-one-dimensional oxides.