Magnetic penetration depth measurements in mgb2 sintered pellets and thin films

We have performed accurate measurements of the temperature dependence of the magnetic penetration depth of the new intermetallic superconductor MgB2 using a high resolution single coil mutual inductance technique. Both sintered pellets and thin films exhibiting critical temperature values ranging between 37 and 38.4 K have been studied. In the case of the film, for T<T-c/2 a clear exponential behavior is observed, which can be explained by a simple BCS s-wave model with a reduced value of the energy gap. On the contrary, pellets show no evidence of saturation, and the experimental results strictly follow a quadratic dependence down to the lowest temperatures. The experimental data on sintered samples can be explained in the framework of a conventional s-wave BCS theory using a two-band model.