Evidence of Josephson junctions in sintered Y${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ samples by means of microwave absorption in a low magnetic field

We present a set of experimental results of microwave absorption (23 GHz) in Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ sintered samples in the presence of an external magnetic field $H$ below 0.1 T. The field dependence in this region may be understood assuming the existence of a random network of Josephson junctions (JJ). The most important experimental facts resulting from our measurements are an exponential-like behavior for the power absorption as a function of the magnetic field $H$, the existence of a critical temperature $T_{\mathrm{cJ}}$ clearly below $T_c$ above which the exponential absorption is no longer present, the behavior as a function of the temperature of a field $H_d\mathrm{}\left(T\right)\mathrm{}$ which is interpreted as a junction dephasing field. We show that the JJ model allows a quantitative fit of the experimental data when a statistical distribution for the junction geometrical parameters is chosen.