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.