The temperature dependence of the real part of the microwave complex conductivity at 17.9GHz obtained from surface impedance measurements of two c-axis oriented MgB2 thin films revealed a pronounced maximum at a temperature around 0.6 times the critical temperature. Calculations in the frame of a 2-band model based on Bardeen-Cooper-Schrieffer theory suggested that this maximum corresponded to an anomalous coherence peak resembling the 2-gap nature of MgB2. The model assumed that there was no interband impurity scattering and a weak interband pairing interaction, as suggested by band structure calculations. In addition, the observation of a coherence peak indicated that the π band was in the dirty limit and dominates the total conductivity of the present films.

Anomalous Coherence Peak in the Microwave Conductivity of c-Axis Oriented MgB2 Thin Films. B.B.Jin, T.Dahm, A.I.Gubin, E.M.Choi, H.J.Kim, S.I.Lee, W.N.Kang, N.Klein: Physical Review Letters, 2003, 91[12], 127006 (3pp)