With a two coil mutual inductance technique the in plane penetration depth in compact YBaCuO films was measured to be λ (0) ≅ 0.23 μm. In granular YBaCuO films the penetration depth is larger, its value is being determined by the strength of the intergranular Josephson coupling energy.
Bibliographical noteFunding Information:
FIGURE 2 Imaginary part of the signal voltage as a function of transverse magnetic field for samples $I and $2. The reduced temperatures labeled a to f are 0.95, 0.96, 0.965, 0.97, 0.975,0.98; g to k are 0.50, 0.65, 0.78, 0.82, and 0.86 Since the kinetic inductance is the additive quantity, one might expect the following relationship between the various I : l~ff= l~b + k~. A more detailed analysis of the penetration-depth in granular films will be presented elswehere. The moat dramatic difference in behavior of the two samples was observed in a perpendicular magnetic field. Figure 2 shows the imaginary part of the signal voltage as a function of magnetic field at different reduced temperatures t ~ T/T 0 . Notice that the magnetic field can penetrate into sample $I only at the highest temperatures : intrinsic YBaCuO properties are measured in this compact sample. Owing to the large upper critical field, up to t ~ 0.95 a magnetic field of 0.5 T has practically no effect on its screening properties. By contrast the data for $2 exhibit a sharp drop at low magnetic fields at all temperatures shown, down to t = 0.5. This initial drop, occurring at a very weakly temperature dependent magnetic field of 200-300 G, can be attributed to a decoupling of the individual grains at low magnetic fields. If we identify this field as the field necessary to nucleate one flux quantum in the junctions between the grains, with the given sample thickness the junction width turns out to be a few tenths of a pm, slightly less than the grain size estimated from optical and scanning electron micrographs. In conclusion, inductive conductance measurements in compact YBaCuO films have yielded an in plane penetration depth X(O) = 0.23 pm. As a function of temperature, I closely follows a (l-t) -I/2 law. In granular films the temperature dependence of X is mere complex, the present analysis yielding only a lower limit for l(O). This work was supported by the Swiss National Science Foundation.