Theoretical analysis of the origin of the double-well band dispersion in the CuO double chains of Pr${}_2$Ba${}_4$Cu${}_7$O${}_{15-\delta }$ and its impact on superconductivity

Abstract

Pr${}_2$Ba${}_4$Cu${}_7$O${}_{15-\delta }$ is a unique member of cuprate superconductors where many studies suggest that CuO double chains are responsible for superconductivity. One characteristic and non-trivial 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 Pr${}_2$Ba${}_4$Cu${}_7$O${}_{15-\delta }$ 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 $|t/t^{\prime }|$ 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 Pr${}_2$Ba${}_4$Cu${}_7$O${}_{15-\delta }$.

9 pages, 9 figures

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