Dependence of penetration depth, microwave surface resistance and energy gap of MgB2 thin films on their normal-state resistivity

The dependences of magnetic field penetration depth at zero temperature lambda(0), microwave surface resistance R-s and pi -band energy gap at zero temperature Delta(pi)(0) on the normal-state resistivity fight above the critical, rho(0), were studied for MgB2 thin films prepared by different temperature. techniques by employing a sapphire resonator technique. We found that the zero-temperature penetration depth lambda(0) data could be well fitted by lambda(L)(1 + xi(0)/l)(1/2) yielding a London penetration depth lambda(L) of 34.5 nm, where xi(0) is the coherence length, and l is the mean free path determined from rho(0). The surface resistance R-s at 15 and 20 K increases roughly linearly with rho(0). The observed increase of Delta(pi)(0) with rho(0) and the decrease of T-c indicate the expected effects of interband impurity scattering within an extended BCS approach. The low values of R-s and lambda(0) in conjunction with the large coherence length for epitaxial films are potentially attractive for applications in electronics and microwave technology.