Magnetically modulated microwave absorption measurement of the penetration depth in a polycrystalline YBa2Cu3O7−x thin film

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Abstract
In previous work, a magnetically modulated microwave absorption (MMMA) technique to measure the Ginzburg–Landau parameter κ=(Λ/ξ) in high-Tc superconductors (bulk samples of YBCO) was described. In this work, how this technique can be applied to the measurement of the London penetration depth Λ is described. Data are reported for the temperature variation of Λ in a well-characterized c-axis-oriented polycrystalline thin film of YBa2Cu3O7−x, prepared by a pulsed laser deposition technique. For low temperatures, Λ(0)≂3640 Å with the microwave electric field oriented parallel to the c axis. The temperature dependence of Λ(0)/Λ(T) can be well described by the two-fluid model. The data are also reasonably fit by a BCS model, however the MMMA technique (in the work here reported) does not have the resolution at low temperatures to obtain strong quantitative evidence for an energy gap Δ (even if it exists).