Superconducting penetration depth of aluminum thin films
David López-Núñez, Alba Torras-Coloma, Queralt Portell-Montserrat, E. Bertoldo, Luis D. Cozzolino, G. A. Ummarino, Alessio Zaccone, Gemma Rius, Manel Martinez, P. Forn-Díaz
Abstract
Abstract We present a study of the superconducting penetration depth λ in aluminum thin films of varying thickness. The range of thicknesses chosen spans from the thin-film regime to the regime approaching bulk behavior. The penetration depths observed range from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>163</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>nm</mml:mi> </mml:mrow> </mml:mrow> </mml:math> for the thinnest 28 nm samples down to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>58</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>nm</mml:mi> </mml:mrow> </mml:mrow> </mml:math> for the 207 nm-thick ones, allowing us to provide an estimate of the thickness at which aluminum becomes a type-I superconductor. In order to accurately determine λ , we performed complementary measurements using the frequency of superconducting LC resonators obtained through novel and efficient methods of fitting and simulation, as well as the normal-state resistance of meandered structures. Both methods yield comparable results, providing a well-characterized set of values of λ in aluminum in the relevant range for applications in fields such as quantum computing and microwave radiation detector technologies.