Vortex State Microwave Resistivity in Tl-2212 Thin Films

We present measurements of the field induced changes in the 47 GHz complex resistivity, Δρ~(H, T), in Tl₂Ba₂CaCu₂O_8+x (TBCCO) thin films with T _c ≃ 105 K, prepared on CeO₂ buffered sapphire substrates. At low fields (μ₀ H < 10 mT) a very small irreversible feature is present, suggesting a little role of intergranular phenomena. Above that level Δρ~(H, T exhibits a superlinear dependence with the field, as opposed to the expected (at high frequencies) quasilinear behaviour. We observe a crossover between predominantly imaginary to predominantly real (dissipative) response with increasing temperature and/or field. In addition, we find the clear scaling property Δρ~(H, T = Δρ~H/H ^* (T)], where the scaling field H ^∗ (T) maps closely the melting field measured in single crystals. We discuss our microwave results in terms of loss of flux lines rigidity.