Determining the Thickness of the Dead Layer in Superconducting Film Using a Two-Coil Mutual-Inductance Technique

A dead layer without superconductivity, i.e., zero resistance and Meissner effect, commonly exists at the interface between substrate and superconducting film. It is demonstrated that the dead layer can significantly degrade the performance of superconducting devices at microwave frequencies. Knowing the thickness of the dead layer, d(dead), is necessary when using a two-coil mutual-inductance (TCMI) technique to measure the absolute value of the magnetic penetration depth, lambda, in superconducting films. However, there is still no established method to determine d(dead) in superconducting films. Here, we propose employing the TCMI technique to determine d(dead), based on a multilayered model in which the dead layer is sandwiched between superconducting layer and substrate. Using this method, we find that d(dead) = 43 +/- 10 nm for our superconducting FeSe films, in agreement with the absence of diamagnetism for the 42-nm-thick film. With the d(dead) determined, we accurately determine the absolute value of lambda in superconducting FeSe films.