Critical chain length and superconductivity emergence in   oxygen-equalized pairs of YBa2Cu3O6.30
  The oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is studied, for the first time in a comparative way, on pair samples having the same oxygen content and thermal history, but different Cu(1)Ox chain arrangements deriving from their intercalated and deintercalated nature. Structural and electronic non-equivalence of pairs samples is detected in the critical region and found to be related, on microscopic scale, to a different average chain length, which, on being experimentally determined by nuclear quadrupole resonance (NQR), sheds new light on the concept of critical chain length for hole doping efficiency. 
P. Manca, G. Calestani, A. Migliori, R. De Renzi, G. Allodi and S.   Sanna