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 in a comparative way on pair samples having the same oxygen conten t and thermal history, but different Cu(1)O-x chain arrangements deriving f rom their intercalated and deintercalated nature. Structural and electronic nonequivalence of pairs samples is detected in the critical. region and fo und to be related, on microscopic scale, to a different average chain lengt h, which, on being experimentally determined by nuclear quadrupole resonanc e (NQR), sheds light on the concept of critical chain length for hole dopin g efficiency.