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

Abstract

The dependences of magnetic field penetration depth at zero temperature λ(0), microwave surface resistance Rs and π-band energy gap at zero temperature Δπ(0) on the normal-state resistivity right above the critical temperature, ρ0, were studied for MgB2 thin films prepared by different techniques by employing a sapphire resonator technique. We found that the zero-temperature penetration depth λ(0) data could be well fitted by yielding a London penetration depth λL of 34.5 nm, where ξ0 is the coherence length, and is the mean free path determined from ρ0. The surface resistance Rs at 15 and 20 K increases roughly linearly with ρ0. The observed increase of Δπ(0) with ρ0 and the decrease of Tc indicate the expected effects of interband impurity scattering within an extended BCS approach. The low values of Rs and λ(0) in conjunction with the large coherence length for epitaxial films are potentially attractive for applications in electronics and microwave technology.