Theoretical analysis of the origin of the double-well band dispersion in the CuO double chains of Pr2Ba4Cu7O15-δ and its impact on superconductivity

Pr2Ba4Cu7O15-delta is a unique member of cuprate superconductors where many studies suggest that CuO double chains are responsible for superconductivity. One characteristic and nontrivial feature of its electronic structure is a relatively large electron hopping t between nearest-neighbor Cu sites with a Cu-O-Cu angle of around 90 degrees. In this study, we have theoretically pinned down the origin of a large |t|in the double-chain structure of Pr2Ba4Cu7O15-delta using first-principles calculation and tight-binding-model analysis. We have found that, in the nearest-neighbor hopping t, d-d, and d-p-p-d contributions roughly cancel each other out and the d-p-d hopping path enhanced by the local distortion of the double chain is a key to get the large |t|. Double-well band dispersion arising from the relatively large |t/t'| allows the enhancement of spin-fluctuation-mediated superconductivity by the incipient-band mechanism, where the one band bottom plays a role of the incipient valley. Our study provides the important knowledge to understand the unique superconductivity in Pr2Ba4Cu7O15-delta.