Inter-site pair superconductivity: origins and recent validation experiments

TL;DR

Recent experiments strongly support the inter-site pairing model for high-temperature superconductivity in cuprates, providing experimental validation for its predictions on doping dependence, lattice dynamics, and carrier behavior.

Contribution

The paper provides comprehensive experimental validation for the inter-site pairing model, linking multiple measurements to its core predictions in cuprate superconductors.

Findings

Superfluid density varies linearly with doping across the phase diagram.

Lattice dynamics measurements match the predicted inter-site pairing behavior.

Time-domain spectroscopy reveals distinct timescales for pairing and superconductivity.

Abstract

The challenge of understanding high-temperature superconductivity has led to a plethora of ideas, but 30 years after its discovery in cuprates, very few have achieved convincing experimental validation. While Hubbard and t-J models were given a lot of attention, a number of recent experiments appear to give decisive support to the model of real-space inter-site pairing and percolative superconductivity in cuprates. Systematic measurements of the doping dependence of the superfluid density show a linear dependence on superfluid density - rather than doping - over the entire phase diagram, in accordance with the model's predictions. The doping-dependence of the anomalous lattice dynamics of in-plane Cu-O mode vibrations observed by inelastic neutron scattering, gives remarkable reciprocal space signature of the inter-site pairing interaction whose doping dependence closely follows the predicted pair density. Symmetry-specific time-domain spectroscopy shows carrier localization, polaron formation, pairing and superconductivity to be distinct processes occurring on distinct timescales throughout the entire superconducting phase diagram. The three diverse experimental results confirm non-trivial predictions made more than a decade ago by the inter-site pairing model in the cuprates, remarkably also confirming some of the fundamental notions mentioned in the seminal paper on the discovery of high-temperature superconductivity in cuprates.