Low-Field Phenomenology and Characteristic Lengths of Hydrogen- and Halogen-Doped YBa2Cu3O7−δ Compounds

We measure the diamagnetic response of YBa2Cu3OyAx (A=Cl, F, H) ceramics. We obtain low-field effective penetration depths λ of a few 10 μm, first flux-penetration field H1distinguishable from the volume penetration field HC1and two characteristic temperatures Tsand Tc, Tc<Ts, defined by the onset of the real and imaginary parts of the susceptibility, respectively. H1(T) goes to zero as a power law H1(T, x)=H1(0, x) (T−T/Tc)2.7near TC. From the values of λ and H1we infer the correlation length ξ at T=4.2 K. A large range of values for ξ(4.2) suggests that chemical disorder plays an essential role in the phenomenology of cuprates. We find λ(4.2)∼H1(4.2)−1/3. This, and the power law ξ(4.2)∼H1(4.2)−2/3result from the scaling properties of a phase transition governed by disorder.