Dresden 2006 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 7: Superconductivity & Solids At Low Temperature - Poster Session

TT 7.8: Poster

Montag, 27. März 2006, 14:00–17:45, P1

Microwave properties of MgB₂ thin films prepared in situ by thermal evaporation combined with sputtering — •Rudolf Schneider, Alexander G. Zaitsev, Roland Hott, Fritz Ratzel, and Jochen Geerk — Forschungszentrum Karlsruhe, Institut für Festkörperphysik, P.O.B. 3640, D-76021 Karlsruhe, Germany

Superconducting MgB₂ thin films were prepared in situ using a combination of rf magnetron sputtering of B and thermal evaporation of Mg. The films exhibited T_c of up to 36 K. Microwave measurements were performed on 14×14 mm² films using both Cu-shielded and Nb-shielded sapphire puck resonators at the frequency of 18.8 GHz. The hf surface resistance (R_s) and the change of the hf surface reactance (ΔX_s) were determined. The films exhibited low R_s matching the literature results for high-quality MgB₂ films. Below 3 K R_s reached 3-5 µΩ which was the resolution limit of our measurement. The temperature dependence of both R_s and ΔX_s were in good agreement with BCS theory. From the R_s(T) dependence we obtained an energy gap Δ(0)≈ 3 meV. The measured variation of the London penetration depth with temperature, Δλ_L(T), was also in good agreement with the BCS model. Using the BCS relation between the energy gap and the penetration depth we fitted our experimental Δλ_L(T) data and obtained λ_L(0) values which ranged for different films from 85 to 100 nm.