title: Anomalous coherence peak in the microwave conductivity of c-axis oriented MgB2 thin films.
abstract: The temperature dependence of the real part of the microwave complex conductivity at 17.9 GHz obtained from surface impedance measurements of two c-axis oriented MgB2 thin films reveals a pronounced maximum at a temperature around 0.6 times the critical temperature. Calculations in the frame of a two-band model based on Bardeen-Cooper-Schrieffer (BCS) theory suggest that this maximum corresponds to an anomalous coherence peak resembling the two-gap nature of MgB2. Our model assumes there is no interband impurity scattering and a weak interband pairing interaction, as suggested by band structure calculations. In addition, the observation of a coherence peak indicates that the pi band is in the dirty limit and dominates the total conductivity of our films.
authors.affiliation: Forschungszentrum Jülich GmbH, Institute of Thin Films and Interfaces, D-52425 Jülich, Germany.
authors.forename: B B
authors.initials: BB
authors.lastname: Jin
authors.forename: T
authors.initials: T
authors.lastname: Dahm
authors.forename: A I
authors.initials: AI
authors.lastname: Gubin
authors.forename: Eun-Mi
authors.initials: EM
authors.lastname: Choi
authors.forename: Hyun Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Sung-Ik
authors.initials: SI
authors.lastname: Lee
authors.forename: W N
authors.initials: WN
authors.lastname: Kang
authors.forename: N
authors.initials: N
authors.lastname: Klein