  The emergence of carrier-pairing from the electronically inhomogeneous phase
of lightly hole-doped copper oxides has been investigated through
magnetoresistance measurements on 1222-type ruthenocuprates
RuSr2(R,Ce)2Cu2O10-d, principally with R = Gd, Sm, Nd. A well-defined
transition at which superconducting fluctuations emerge is discovered at a
remarkably low critical doping, pc = 0.0084, deep within the antiferromagnetic
phase. Systematic variations of the low temperature fluctuation density with
doping and cell volume demonstrate the intrinsic nature of the electronic
inhomogeneity and provide new support for bosonic models of the superconducting
mechanism.
