Unravelling the role of Cu-O chain length on the superconducting properties of

The superconducting properties of the $\rm SmBa_2Cu_3O_{6+\delta}$ 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 $\rm SmBa_2Cu_3O_{6+\delta}$ 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