Dependence of penetration depth, microwave surface resistance and energy gap ofMgB2 thin films on their normal-state resistivity

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The dependences of magnetic field penetration depth at zero temperatureλ(0), microwave surfaceresistance Rs andπ-band energy gap atzero temperature Δπ(0) on the normal-state resistivity right above the critical temperature,ρ0, werestudied for MgB2 thin films prepared by different techniques by employing a sapphireresonator technique. We found that the zero-temperature penetration depthλ(0) data could be well fitted by yielding a London penetration depthλL of 34.5 nm,where ξ0 is the coherence length, and is the mean free path determined fromρ0. The surfaceresistance Rs at 15 and 20 K increases roughly linearly withρ0. The observedincrease of Δπ(0) with ρ0 and thedecrease of Tc indicate the expected effects of interband impurity scattering within an extended BCS approach. The lowvalues of Rs and λ(0) in conjunction with the large coherence length for epitaxial films are potentially attractivefor applications in electronics and microwave technology.