Anomalous microwave conductivity coherence peak in c-axis MgB2 thin film

TL;DR

This study observes an anomalous microwave conductivity coherence peak in c-axis MgB2 thin films, indicating a two-gap superconductivity behavior and the dirty limit of the pi-band, based on experimental and theoretical analysis.

Contribution

It provides experimental evidence of a coherence peak in MgB2 thin films and models it using a two-band BCS framework with specific assumptions about impurity scattering.

Findings

Pronounced maximum in microwave conductivity at 0.6 T_c

Peak attributed to two-gap superconductivity in MgB2

Pi-band in the dirty limit dominates conductivity

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 bandstructure 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