Beyond-Hubbard pairing in a cuprate ladder

TL;DR

This study reveals that magnetic excitations in a cuprate ladder differ from the Hubbard model predictions, indicating enhanced hole pairing due to strong attractive interactions, which may be a universal feature of cuprate superconductors.

Contribution

It demonstrates that an extended pairing mechanism beyond the Hubbard model explains magnetic excitations and hole pairing in cuprate ladders, suggesting universality in cuprate superconductivity.

Findings

Magnetic excitations are inconsistent with a simple Hubbard model.

Hole carrier response is strongly suppressed due to d-wave-like pairing.

Large nearest-neighbor attraction enhances hole pairing by nearly an order of magnitude.

Abstract

The Hubbard model is believed to capture the essential physics of cuprate superconductors. However, recent theoretical studies suggest that it fails to reproduce a robust and homogeneous superconducting ground state. Here, using resonant inelastic x-ray scattering and density matrix renormalization group calculations, we show that magnetic excitations in the prototypical cuprate ladder Sr$_{14}$Cu$_{24}$O$_{41}$ are inconsistent with those of a simple Hubbard model. The magnetic response of hole carriers, contributing to an emergent branch of spin excitations, is strongly suppressed. This effect is the consequence of d-wave-like pairing, enhanced by nearly an order of magnitude through a large nearest-neighbor attractive interaction. The similarity between cuprate ladders and the two-dimensional compounds suggests that such an enhanced hole pairing may be a universal feature of superconducting cuprates.