Unravelling the role of Cu-O chain length on the superconducting properties of SmBa2Cu3O6 + δ via Al doping and clustering

The superconducting properties of the SmBa2Cu3O6 + delta superconductor change dramatically upon oxidation. The driving force for these changes is still under debate because many concomitant structural changes occur. In order to highlight the specific role of Cu-O chain ordering on the rise of superconductivity in this system, Al-doped SmBa2Cu3O6 + delta samples have been examined, having equal aluminium and oxygen concentration and nearly the same structure but different mean length of Cu-O chain fragments. For the first time, it is clearly shown that, keeping all the other structural properties unchanged, the local increase of the chain length determines a significant enhancement of the superconducting properties, i.e. TC and Meissner fraction.