Inter-site pair superconductivity: Origins and recent validation experiments

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 [1–3] and percolative superconductivity [4] in cuprates. Systematic measurements of the doping dependence of the superfluid density ρs show a linear dependence on Tc—rather than doping—over the entire phase diagram [5], 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 [6], gives remarkable reciprocal space signature of the inter-site pairing interaction [1] 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 [7].